fbpx
Wikipedia

Soil

For other uses, see Soil (disambiguation).
Look up soil in Wiktionary, the free dictionary.

Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions:

A, B, and C represent the soil profile, a notation firstly coined by Vasily Dokuchaev (1846–1903), the father of pedology; A is the topsoil; B is a regolith; C is a saprolite (a less-weathered regolith); the bottom-most layer represents the bedrock.
Surface-water-gley developed in glacial till, Northern Ireland.

All of these functions, in their turn, modify the soil and its properties.

Soil is also commonly referred to as earth or dirt; some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.

The pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere. The term pedolith, used commonly to refer to the soil, translates to ground stone in the sense fundamental stone, from the ancient Greekπέδον 'ground, earth'. Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soil scientists can envisage soils as a three-state system of solids, liquids, and gases.

Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem.

Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean.

Soil science has two basic branches of study: edaphology and pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation, description (morphology), and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects.

Contents

Soil functions as a major component of the Earth's ecosystem. The world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, with effects ranging from ozone depletion and global warming to rainforest destruction and water pollution. With respect to Earth's carbon cycle, soil acts as an important carbon reservoir, and it is potentially one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback (amplification). This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover.

Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, and a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains a prominent part of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely still unexplored. Soil has a mean prokaryotic density of roughly 108 organisms per gram, whereas the ocean has no more than 107 prokaryotic organisms per milliliter (gram) of seawater. Organic carbon held in soil is eventually returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter; tillage usually increases the rate of soil respiration, leading to the depletion of soil organic matter. Since plant roots need oxygen, aeration is an important characteristic of soil. This ventilation can be accomplished via networks of interconnected soil pores, which also absorb and hold rainwater making it readily available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival.

Soils can effectively remove impurities, kill disease agents, and degrade contaminants, this latter property being called natural attenuation. Typically, soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, air, water, temperature moderation, nutrients, and protection from toxins. Soils provide readily available nutrients to plants and animals by converting dead organic matter into various nutrient forms.

Soil profile: Darkened topsoil and reddish subsoil layers are typical of humid subtropical climate regions

Components of a silt loam soil by percent volume

Water (25%)
Gases (25%)
Sand (18%)
Silt (18%)
Clay (9%)
Organic matter (5%)

A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% voids (or pores) of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other. The pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms.

Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons. These differ in one or more properties such as in their texture, structure, density, porosity, consistency, temperature, color, and reactivity. The horizons differ greatly in thickness and generally lack sharp boundaries; their development is dependent on the type of parent material, the processes that modify those parent materials, and the soil-forming factors that influence those processes. The biological influences on soil properties are strongest near the surface, while the geochemical influences on soil properties increase with depth. Mature soil profiles typically include three basic master horizons: A, B, and C. The solum normally includes the A and B horizons. The living component of the soil is largely confined to the solum, and is generally more prominent in the A horizon. It has been suggested that the pedon, a column of soil extending vertically from the surface to the underlying parent material and large enough to show the characteristics of all its horizons, could be subdivided in the humipedon (the living part, where most soil organisms are dwelling, corresponding to the humus form), the copedon (in intermediary position, where most weathering of minerals takes place) and the lithopedon (in contact with the subsoil).

The soil texture is determined by the relative proportions of the individual particles of sand, silt, and clay that make up the soil. The interaction of the individual mineral particles with organic matter, water, gases via biotic and abiotic processes causes those particles to flocculate (stick together) to form aggregates or peds. Where these aggregates can be identified, a soil can be said to be developed, and can be described further in terms of color, porosity, consistency, reaction (acidity), etc.

Water is a critical agent in soil development due to its involvement in the dissolution, precipitation, erosion, transport, and deposition of the materials of which a soil is composed. The mixture of water and dissolved or suspended materials that occupy the soil pore space is called the soil solution. Since soil water is never pure water, but contains hundreds of dissolved organic and mineral substances, it may be more accurately called the soil solution. Water is central to the dissolution, precipitation and leaching of minerals from the soil profile. Finally, water affects the type of vegetation that grows in a soil, which in turn affects the development of the soil, a complex feedback which is exemplified in the dynamics of banded vegetation patterns in semi-arid regions.

Soils supply plants with nutrients, most of which are held in place by particles of clay and organic matter (colloids) The nutrients may be adsorbed on clay mineral surfaces, bound within clay minerals (absorbed), or bound within organic compounds as part of the living organisms or dead soil organic matter. These bound nutrients interact with soil water to buffer the soil solution composition (attenuate changes in the soil solution) as soils wet up or dry out, as plants take up nutrients, as salts are leached, or as acids or alkalis are added.

Plant nutrient availability is affected by soil pH, which is a measure of the hydrogen ion activity in the soil solution. Soil pH is a function of many soil forming factors, and is generally lower (more acid) where weathering is more advanced.

Most plant nutrients, with the exception of nitrogen, originate from the minerals that make up the soil parent material. Some nitrogen originates from rain as dilute nitric acid and ammonia, but most of the nitrogen is available in soils as a result of nitrogen fixation by bacteria. Once in the soil-plant system, most nutrients are recycled through living organisms, plant and microbial residues (soil organic matter), mineral-bound forms, and the soil solution. Both living soil organisms (microbes, animals and plant roots) and soil organic matter are of critical importance to this recycling, and thereby to soil formation and soil fertility. Microbial soil enzymes may release nutrients from minerals or organic matter for use by plants and other microorganisms, sequester (incorporate) them into living cells, or cause their loss from the soil by volatilisation (loss to the atmosphere as gases) or leaching.

Main article: Pedogenesis
Further information: Soil mechanics § Genesis

Soil formation, or pedogenesis, is the combined effect of physical, chemical, biological and anthropogenic processes working on soil parent material. Soil is said to be formed when organic matter has accumulated and colloids are washed downward, leaving deposits of clay, humus, iron oxide, carbonate, and gypsum, producing a distinct layer called the B horizon. This is a somewhat arbitrary definition as mixtures of sand, silt, clay and humus will support biological and agricultural activity before that time. These constituents are moved from one level to another by water and animal activity. As a result, layers (horizons) form in the soil profile. The alteration and movement of materials within a soil causes the formation of distinctive soil horizons. However, more recent definitions of soil embrace soils without any organic matter, such as those regoliths that formed on Mars and analogous conditions in planet Earth deserts.

An example of the development of a soil would begin with the weathering of lava flow bedrock, which would produce the purely mineral-based parent material from which the soil texture forms. Soil development would proceed most rapidly from bare rock of recent flows in a warm climate, under heavy and frequent rainfall. Under such conditions, plants (in a first stage nitrogen-fixing lichens and cyanobacteria then epilithic higher plants) become established very quickly on basaltic lava, even though there is very little organic material. Basaltic minerals commonly weather relatively quickly, according to the Goldich dissolution series.The plants are supported by the porous rock as it is filled with nutrient-bearing water that carries minerals dissolved from the rocks. Crevasses and pockets, local topography of the rocks, would hold fine materials and harbour plant roots. The developing plant roots are associated with mineral-weathering mycorrhizal fungi that assist in breaking up the porous lava, and by these means organic matter and a finer mineral soil accumulate with time. Such initial stages of soil development have been described on volcanoes, inselbergs, and glacial moraines.

How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil. They are: parent material, climate, topography (relief), organisms, and time. When reordered to climate, relief, organisms, parent material, and time, they form the acronym CROPT.

The physical properties of soils, in order of decreasing importance for ecosystem services such as crop production, are texture, structure, bulk density, porosity, consistency, temperature, colour and resistivity. Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand, silt, and clay. At the next larger scale, soil structures called peds or more commonly soil aggregates are created from the soil separates when iron oxides, carbonates, clay, silica and humus, coat particles and cause them to adhere into larger, relatively stable secondary structures. Soil bulk density, when determined at standardized moisture conditions, is an estimate of soil compaction. Soil porosity consists of the void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining. Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil. These properties vary through the depth of a soil profile, i.e. through soil horizons. Most of these properties determine the aeration of the soil and the ability of water to infiltrate and to be held within the soil.

Main article: Soil moisture

Soil moisture refers to the water content of the soil. It can be expressed in terms of volume or weight. Soil moisture measurement can be based on in situ probes (e.g., capacitance probes, neutron probes) or remote sensing methods.

Main article: Soil gas

The atmosphere of soil, or soil gas, is very different from the atmosphere above. The consumption of oxygen by microbes and plant roots, and their release of carbon dioxide, decrease oxygen and increase carbon dioxide concentration. Atmospheric CO2 concentration is 0.04%, but in the soil pore space it may range from 10 to 100 times that level, thus potentially contributing to the inhibition of root respiration. Calcareous soils regulate CO2 concentration by carbonate buffering, contrary to acid soils in which all CO2 respired accumulates in the soil pore system. At extreme levels CO2 is toxic. This suggests a possible negative feedback control of soil CO2 concentration through its inhibitory effects on root and microbial respiration (also called 'soil respiration'). In addition, the soil voids are saturated with water vapour, at least until the point of maximal hygroscopicity, beyond which a vapour-pressure deficit occurs in the soil pore space. Adequate porosity is necessary, not just to allow the penetration of water, but also to allow gases to diffuse in and out. Movement of gases is by diffusion from high concentrations to lower, the diffusion coefficient decreasing with soil compaction. Oxygen from above atmosphere diffuses in the soil where it is consumed and levels of carbon dioxide in excess of above atmosphere diffuse out with other gases (including greenhouse gases) as well as water. Soil texture and structure strongly affect soil porosity and gas diffusion. It is the total pore space (porosity) of soil, not the pore size, and the degree of pore interconnection (or conversely pore sealing), together with water content, air turbulence and temperature, that determine the rate of diffusion of gases into and out of soil. Platy soil structure and soil compaction (low porosity) impede gas flow, and a deficiency of oxygen may encourage anaerobic bacteria to reduce (strip oxygen) from nitrate NO3 to the gases N2, N2O, and NO, which are then lost to the atmosphere, thereby depleting the soil of nitrogen, a detrimental process called denitrification. Aerated soil is also a net sink of methane CH4 but a net producer of methane (a strong heat-absorbing greenhouse gas) when soils are depleted of oxygen and subject to elevated temperatures.

Soil atmosphere is also the seat of emissions of volatiles other than carbon and nitrogen oxides from various soil organisms, e.g. roots, bacteria, fungi, animals. These volatiles are used as chemical cues, making soil atmosphere the seat of interaction networks playing a decisive role in the stability, dynamics and evolution of soil ecosystems. Biogenic soil volatile organic compounds are exchanged with the aboveground atmosphere, in which they are just 1–2 orders of magnitude lower than those from aboveground vegetation.

Humans can get some idea of the soil atmosphere through the well-known 'after-the-rain' scent, when infiltering rainwater flushes out the whole soil atmosphere after a drought period, or when soil is excavated, a bulk property attributed in a reductionist manner to particular biochemical compounds such as petrichor or geosmin.

Main article: Soil matrix

Soil particles can be classified by their chemical composition (mineralogy) as well as their size. The particle size distribution of a soil, its texture, determines many of the properties of that soil, in particular hydraulic conductivity and water potential, but the mineralogy of those particles can strongly modify those properties. The mineralogy of the finest soil particles, clay, is especially important.

The chemistry of a soil determines its ability to supply available plant nutrients and affects its physical properties and the health of its living population. In addition, a soil's chemistry also determines its corrosivity, stability, and ability to absorb pollutants and to filter water. It is the surface chemistry of mineral and organic colloids that determines soil's chemical properties. A colloid is a small, insoluble particle ranging in size from 1 nanometer to 1 micrometer, thus small enough to remain suspended by Brownian motion in a fluid medium without settling. Most soils contain organic colloidal particles called humus as well as the inorganic colloidal particles of clays. The very high specific surface area of colloids and their net electrical charges give soil its ability to hold and release ions. Negatively charged sites on colloids attract and release cations in what is referred to as cation exchange. Cation-exchange capacity (CEC) is the amount of exchangeable cations per unit weight of dry soil and is expressed in terms of milliequivalents of positively charged ions per 100 grams of soil (or centimoles of positive charge per kilogram of soil; cmolc/kg). Similarly, positively charged sites on colloids can attract and release anions in the soil giving the soil anion exchange capacity (AEC).

Cation and anion exchange

Further information: Cation-exchange capacity

The cation exchange, that takes place between colloids and soil water, buffers (moderates) soil pH, alters soil structure, and purifies percolating water by adsorbing cations of all types, both useful and harmful.

The negative or positive charges on colloid particles make them able to hold cations or anions, respectively, to their surfaces. The charges result from four sources.

  1. Isomorphous substitution occurs in clay during its formation, when lower-valence cations substitute for higher-valence cations in the crystal structure. Substitutions in the outermost layers are more effective than for the innermost layers, as the electric charge strength drops off as the square of the distance. The net result is oxygen atoms with net negative charge and the ability to attract cations.
  2. Edge-of-clay oxygen atoms are not in balance ionically as the tetrahedral and octahedral structures are incomplete.
  3. Hydroxyls may substitute for oxygens of the silica layers, a process called hydroxylation. When the hydrogens of the clay hydroxyls are ionised into solution, they leave the oxygen with a negative charge (anionic clays).
  4. Hydrogens of humus hydroxyl groups may also be ionised into solution, leaving, similarly to clay, an oxygen with a negative charge.

Cations held to the negatively charged colloids resist being washed downward by water and are out of reach of plant roots, thereby preserving the fertility of soils in areas of moderate rainfall and low temperatures.

There is a hierarchy in the process of cation exchange on colloids, as cations differ in the strength of adsorption by the colloid and hence their ability to replace one another (ion exchange). If present in equal amounts in the soil water solution:

Al3+ replaces H+ replaces Ca2+ replaces Mg2+ replaces K+ same as NH4+ replaces Na+

If one cation is added in large amounts, it may replace the others by the sheer force of its numbers. This is called law of mass action. This is largely what occurs with the addition of cationic fertilisers (potash, lime).

As the soil solution becomes more acidic (low pH, meaning an abundance of H+), the other cations more weakly bound to colloids are pushed into solution as hydrogen ions occupy exchange sites (protonation). A low pH may cause the hydrogen of hydroxyl groups to be pulled into solution, leaving charged sites on the colloid available to be occupied by other cations. This ionisation of hydroxy groups on the surface of soil colloids creates what is described as pH-dependent surface charges. Unlike permanent charges developed by isomorphous substitution, pH-dependent charges are variable and increase with increasing pH. Freed cations can be made available to plants but are also prone to be leached from the soil, possibly making the soil less fertile. Plants are able to excrete H+ into the soil through the synthesis of organic acids and by that means, change the pH of the soil near the root and push cations off the colloids, thus making those available to the plant.

Cation exchange capacity (CEC)

Cation exchange capacity should be thought of as the soil's ability to remove cations from the soil water solution and sequester those to be exchanged later as the plant roots release hydrogen ions to the solution. CEC is the amount of exchangeable hydrogen cation (H+) that will combine with 100 grams dry weight of soil and whose measure is one milliequivalents per 100 grams of soil (1 meq/100 g). Hydrogen ions have a single charge and one-thousandth of a gram of hydrogen ions per 100 grams dry soil gives a measure of one milliequivalent of hydrogen ion. Calcium, with an atomic weight 40 times that of hydrogen and with a valence of two, converts to (40/2) x 1 milliequivalent = 20 milliequivalents of hydrogen ion per 100 grams of dry soil or 20 meq/100 g. The modern measure of CEC is expressed as centimoles of positive charge per kilogram (cmol/kg) of oven-dry soil.

Most of the soil's CEC occurs on clay and humus colloids, and the lack of those in hot, humid, wet climates (e.g. tropical rainforests), due to leaching and decomposition, respectively, explains the apparent sterility of tropical soils. Live plant roots also have some CEC, linked to their specific surface area.

Cation exchange capacity for soils; soil textures; soil colloids
Soil State CEC meq/100 g
Charlotte fine sand Florida 1.0
Ruston fine sandy loam Texas 1.9
Glouchester loam New Jersey 11.9
Grundy silt loam Illinois 26.3
Gleason clay loam California 31.6
Susquehanna clay loam Alabama 34.3
Davie mucky fine sand Florida 100.8
Sands ------ 1–5
Fine sandy loams ------ 5–10
Loams and silt loams ----- 5–15
Clay loams ----- 15–30
Clays ----- over 30
Sesquioxides ----- 0–3
Kaolinite ----- 3–15
Illite ----- 25–40
Montmorillonite ----- 60–100
Vermiculite (similar to illite) ----- 80–150
Humus ----- 100–300

Anion exchange capacity (AEC)

Anion exchange capacity should be thought of as the soil's ability to remove anions (e.g. nitrate, phosphate) from the soil water solution and sequester those for later exchange as the plant roots release carbonate anions to the soil water solution. Those colloids which have low CEC tend to have some AEC. Amorphous and sesquioxide clays have the highest AEC, followed by the iron oxides. Levels of AEC are much lower than for CEC, because of the generally higher rate of positively (versus negatively) charged surfaces on soil colloids, to the exception of variable-charge soils. Phosphates tend to be held at anion exchange sites.

Iron and aluminum hydroxide clays are able to exchange their hydroxide anions (OH) for other anions. The order reflecting the strength of anion adhesion is as follows:

H2PO4 replaces SO42− replaces NO3 replaces Cl

The amount of exchangeable anions is of a magnitude of tenths to a few milliequivalents per 100 g dry soil. As pH rises, there are relatively more hydroxyls, which will displace anions from the colloids and force them into solution and out of storage; hence AEC decreases with increasing pH (alkalinity).

Reactivity (pH)

Soil reactivity is expressed in terms of pH and is a measure of the acidity or alkalinity of the soil. More precisely, it is a measure of hydronium concentration in an aqueous solution and ranges in values from 0 to 14 (acidic to basic) but practically speaking for soils, pH ranges from 3.5 to 9.5, as pH values beyond those extremes are toxic to life forms.

At 25 °C an aqueous solution that has a pH of 3.5 has 10−3.5 moles H3O+ (hydronium ions) per litre of solution (and also 10−10.5 mole/litre OH). A pH of 7, defined as neutral, has 10−7 moles of hydronium ions per litre of solution and also 10−7 moles of OH per litre; since the two concentrations are equal, they are said to neutralise each other. A pH of 9.5 has 10−9.5 moles hydronium ions per litre of solution (and also 10−2.5 mole per litre OH). A pH of 3.5 has one million times more hydronium ions per litre than a solution with pH of 9.5 (9.5–3.5 = 6 or 106) and is more acidic.

The effect of pH on a soil is to remove from the soil or to make available certain ions. Soils with high acidity tend to have toxic amounts of aluminium and manganese. As a result of a trade-off between toxicity and requirement most nutrients are better available to plants at moderate pH, although most minerals are more soluble in acid soils. Soil organisms are hindered by high acidity, and most agricultural crops do best with mineral soils of pH 6.5 and organic soils of pH 5.5. Given that at low pH toxic metals (e.g. cadmium, zinc, lead) are positively charged as cations and organic pollutants are in non-ionic form, thus both made more available to organisms, it has been suggested that plants, animals and microbes commonly living in acid soils are pre-adapted to every kind of pollution, whether of natural or human origin.

In high rainfall areas, soils tend to acidify as the basic cations are forced off the soil colloids by the mass action of hydronium ions from usual or unusual rain acidity against those attached to the colloids. High rainfall rates can then wash the nutrients out, leaving the soil inhabited only by those organisms which are particularly efficient to uptake nutrients in very acid conditions, like in tropical rainforests. Once the colloids are saturated with H3O+, the addition of any more hydronium ions or aluminum hydroxyl cations drives the pH even lower (more acidic) as the soil has been left with no buffering capacity. In areas of extreme rainfall and high temperatures, the clay and humus may be washed out, further reducing the buffering capacity of the soil. In low rainfall areas, unleached calcium pushes pH to 8.5 and with the addition of exchangeable sodium, soils may reach pH 10. Beyond a pH of 9, plant growth is reduced. High pH results in low micro-nutrient mobility, but water-soluble chelates of those nutrients can correct the deficit. Sodium can be reduced by the addition of gypsum (calcium sulphate) as calcium adheres to clay more tightly than does sodium causing sodium to be pushed into the soil water solution where it can be washed out by an abundance of water.

Base saturation percentage

There are acid-forming cations (e.g. hydronium, aluminium, iron) and there are base-forming cations (e.g. calcium, magnesium, sodium). The fraction of the negatively-charged soil colloid exchange sites (CEC) that are occupied by base-forming cations is called base saturation. If a soil has a CEC of 20 meq and 5 meq are aluminium and hydronium cations (acid-forming), the remainder of positions on the colloids (20-5 = 15 meq) are assumed occupied by base-forming cations, so that the base saturation is 15/20 x 100% = 75% (the compliment 25% is assumed acid-forming cations). Base saturation is almost in direct proportion to pH (it increases with increasing pH). It is of use in calculating the amount of lime needed to neutralise an acid soil (lime requirement). The amount of lime needed to neutralize a soil must take account of the amount of acid forming ions on the colloids (exchangeable acidity), not just those in the soil water solution (free acidity). The addition of enough lime to neutralize the soil water solution will be insufficient to change the pH, as the acid forming cations stored on the soil colloids will tend to restore the original pH condition as they are pushed off those colloids by the calcium of the added lime.

Buffering

Further information: Soil conditioner

The resistance of soil to change in pH, as a result of the addition of acid or basic material, is a measure of the buffering capacity of a soil and (for a particular soil type) increases as the CEC increases. Hence, pure sand has almost no buffering ability, while soils high in colloids (whether mineral or organic) have high buffering capacity. Buffering occurs by cation exchange and neutralisation. However, colloids are not the only regulators of soil pH. The role of carbonates should be underlined, too. More generally, according to pH levels, several buffer systems take precedence over each other, from calcium carbonate buffer range to iron buffer range.

The addition of a small amount of highly basic aqueous ammonia to a soil will cause the ammonium to displace hydronium ions from the colloids, and the end product is water and colloidally fixed ammonium, but little permanent change overall in soil pH.

The addition of a small amount of lime, Ca(OH)2, will displace hydronium ions from the soil colloids, causing the fixation of calcium to colloids and the evolution of CO2 and water, with little permanent change in soil pH.

The above are examples of the buffering of soil pH. The general principal is that an increase in a particular cation in the soil water solution will cause that cation to be fixed to colloids (buffered) and a decrease in solution of that cation will cause it to be withdrawn from the colloid and moved into solution (buffered). The degree of buffering is often related to the CEC of the soil; the greater the CEC, the greater the buffering capacity of the soil.

Plant nutrients, their chemical symbols, and the ionic forms common in soils and available for plant uptake
Element Symbol Ion or molecule
Carbon C CO2 (mostly through leaves)
Hydrogen H H+, HOH (water)
Oxygen O O2−, OH, CO32−, SO42−, CO2
Phosphorus P H2PO4, HPO42− (phosphates)
Potassium K K+
Nitrogen N NH4+, NO3 (ammonium, nitrate)
Sulfur S SO42−
Calcium Ca Ca2+
Iron Fe Fe2+, Fe3+ (ferrous, ferric)
Magnesium Mg Mg2+
Boron B H3BO3, H2BO3, B(OH)4
Manganese Mn Mn2+
Copper Cu Cu2+
Zinc Zn Zn2+
Molybdenum Mo MoO42− (molybdate)
Chlorine Cl Cl (chloride)

Seventeen elements or nutrients are essential for plant growth and reproduction. They are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), nickel (Ni) and chlorine (Cl). Nutrients required for plants to complete their life cycle are considered essential nutrients. Nutrients that enhance the growth of plants but are not necessary to complete the plant's life cycle are considered non-essential. With the exception of carbon, hydrogen and oxygen, which are supplied by carbon dioxide and water, and nitrogen, provided through nitrogen fixation, the nutrients derive originally from the mineral component of the soil. The Law of the Minimum expresses that when the available form of a nutrient is not in enough proportion in the soil solution, then other nutrients cannot be taken up at an optimum rate by a plant. A particular nutrient ratio of the soil solution is thus mandatory for optimizing plant growth, a value which might differ from nutrient ratios calculated from plant composition.

Plant uptake of nutrients can only proceed when they are present in a plant-available form. In most situations, nutrients are absorbed in an ionic form from (or together with) soil water. Although minerals are the origin of most nutrients, and the bulk of most nutrient elements in the soil is held in crystalline form within primary and secondary minerals, they weather too slowly to support rapid plant growth. For example, the application of finely ground minerals, feldspar and apatite, to soil seldom provides the necessary amounts of potassium and phosphorus at a rate sufficient for good plant growth, as most of the nutrients remain bound in the crystals of those minerals.

The nutrients adsorbed onto the surfaces of clay colloids and soil organic matter provide a more accessible reservoir of many plant nutrients (e.g. K, Ca, Mg, P, Zn). As plants absorb the nutrients from the soil water, the soluble pool is replenished from the surface-bound pool. The decomposition of soil organic matter by microorganisms is another mechanism whereby the soluble pool of nutrients is replenished – this is important for the supply of plant-available N, S, P, and B from soil.

Gram for gram, the capacity of humus to hold nutrients and water is far greater than that of clay minerals, most of the soil cation exchange capacity arising from charged carboxylic groups on organic matter. However, despite the great capacity of humus to retain water once water-soaked, its high hydrophobicity decreases its wettability. All in all, small amounts of humus may remarkably increase the soil's capacity to promote plant growth.

Main article: Soil organic matter
This section may contain an excessive amount of intricate detail that may interest only a particular audience. Specifically, details could be moved into main article. Please help by spinning off or relocating any relevant information, and removing excessive detail that may be against Wikipedia's inclusion policy.(April 2021) ()

Soil organic matter is made up of organic compounds and includes plant, animal and microbial material, both living and dead. A typical soil has a biomass composition of 70% microorganisms, 22% macrofauna, and 8% roots. The living component of an acre of soil may include 900 lb of earthworms, 2400 lb of fungi, 1500 lb of bacteria, 133 lb of protozoa and 890 lb of arthropods and algae.

A few percent of the soil organic matter, with small residence time, consists of the microbial biomass and metabolites of bacteria, molds, and actinomycetes that work to break down the dead organic matter. Were it not for the action of these micro-organisms, the entire carbon dioxide part of the atmosphere would be sequestered as organic matter in the soil. However, in the same time soil microbes contribute to carbon sequestration in the topsoil through the formation of stable humus. In the aim to sequester more carbon in the soil for alleviating the greenhouse effect it would be more efficient in the long-term to stimulate humification than to decrease litter decomposition.

The main part of soil organic matter is a complex assemblage of small organic molecules, collectively called humus or humic substances. The use of these terms, which do not rely on a clear chemical classification, has been considered as obsolete. Other studies showed that the classical notion of molecule is not convenient for humus, which escaped most attempts done over two centuries to resolve it in unit components, but still is chemically distinct from polysaccharides, lignins and proteins.

Most living things in soils, including plants, animals, bacteria, and fungi, are dependent on organic matter for nutrients and/or energy. Soils have organic compounds in varying degrees of decomposition which rate is dependent on temperature, soil moisture, and aeration. Bacteria and fungi feed on the raw organic matter, which are fed upon by protozoa, which in turn are fed upon by nematodes, annelids and arthropods, themselves able to consume and transform raw or humified organic matter. This has been called the soil food web, through which all organic matter is processed as in a digestive system. Organic matter holds soils open, allowing the infiltration of air and water, and may hold as much as twice its weight in water. Many soils, including desert and rocky-gravel soils, have little or no organic matter. Soils that are all organic matter, such as peat (histosols), are infertile. In its earliest stage of decomposition, the original organic material is often called raw organic matter. The final stage of decomposition is called humus.

In grassland, much of the organic matter added to the soil is from the deep, fibrous, grass root systems. By contrast, tree leaves falling on the forest floor are the principal source of soil organic matter in the forest. Another difference is the frequent occurrence in the grasslands of fires that destroy large amounts of aboveground material but stimulate even greater contributions from roots. Also, the much greater acidity under any forests inhibits the action of certain soil organisms that otherwise would mix much of the surface litter into the mineral soil. As a result, the soils under grasslands generally develop a thicker A horizon with a deeper distribution of organic matter than in comparable soils under forests, which characteristically store most of their organic matter in the forest floor (O horizon) and thin A horizon.

Humus

Humus refers to organic matter that has been decomposed by soil microflora and fauna to the point where it is resistant to further breakdown. Humus usually constitutes only five percent of the soil or less by volume, but it is an essential source of nutrients and adds important textural qualities crucial to soil health and plant growth. Humus also feeds arthropods, termites and earthworms which further improve the soil. The end product, humus, is suspended in colloidal form in the soil solution and forms a weak acid that can attack silicate minerals by chelating their iron and aluminum atoms. Humus has a high cation and anion exchange capacity that on a dry weight basis is many times greater than that of clay colloids. It also acts as a buffer, like clay, against changes in pH and soil moisture.

Humic acids and fulvic acids, which begin as raw organic matter, are important constituents of humus. After the death of plants, animals, and microbes, microbes begin to feed on the residues through their production of extra-cellular soil enzymes, resulting finally in the formation of humus. As the residues break down, only molecules made of aliphatic and aromatic hydrocarbons, assembled and stabilized by oxygen and hydrogen bonds, remain in the form of complex molecular assemblages collectively called humus. Humus is never pure in the soil, because it reacts with metals and clays to form complexes which further contribute to its stability and to soil structure. While the structure of humus has in itself few nutrients (with the exception of constitutive metals such as calcium, iron and aluminum) it is able to attract and link, by weak bonds, cation and anion nutrients that can further be released into the soil solution in response to selective root uptake and changes in soil pH, a process of paramount importance for the maintenance of fertility in tropical soils.

Lignin is resistant to breakdown and accumulates within the soil. It also reacts with proteins, which further increases its resistance to decomposition, including enzymatic decomposition by microbes. Fats and waxes from plant matter have still more resistance to decomposition and persist in soils for thousand years, hence their use as tracers of past vegetation in buried soil layers. Clay soils often have higher organic contents that persist longer than soils without clay as the organic molecules adhere to and are stabilised by the clay. Proteins normally decompose readily, to the exception of scleroproteins, but when bound to clay particles they become more resistant to decomposition. As for other proteins clay particles absorb the enzymes exuded by microbes, decreasing enzyme activity while protecting extracellular enzymes from degradation. The addition of organic matter to clay soils can render that organic matter and any added nutrients inaccessible to plants and microbes for many years, while a study showed increased soil fertility following the addition of mature compost to a clay soil. High soil tannin content can cause nitrogen to be sequestered as resistant tannin-protein complexes.

Humus formation is a process dependent on the amount of plant material added each year and the type of base soil. Both are affected by climate and the type of organisms present. Soils with humus can vary in nitrogen content but typically have 3 to 6 percent nitrogen. Raw organic matter, as a reserve of nitrogen and phosphorus, is a vital component affecting soil fertility. Humus also absorbs water, and expands and shrinks between dry and wet states to a higher extent than clay, increasing soil porosity. Humus is less stable than the soil's mineral constituents, as it is reduced by microbial decomposition, and over time its concentration diminishes without the addition of new organic matter. However, humus in its most stable forms may persist over centuries if not millennia. Charcoal is a source of highly stable humus, called black carbon, which had been used traditionally to improve the fertility of nutrient-poor tropical soils. This very ancient practice, as ascertained in the genesis of Amazonian dark earths, has been renewed and became popular under the name of biochar. It has been suggested that biochar could be used to sequester more carbon in the fight against the greenhouse effect.

Climatological influence

The production, accumulation and degradation of organic matter are greatly dependent on climate. For example, when a thawing event occurs, the flux of soil gases with atmospheric gases is significantly influenced. Temperature, soil moisture and topography are the major factors affecting the accumulation of organic matter in soils. Organic matter tends to accumulate under wet or cold conditions where decomposer activity is impeded by low temperature or excess moisture which results in anaerobic conditions. Conversely, excessive rain and high temperatures of tropical climates enables rapid decomposition of organic matter and leaching of plant nutrients. Forest ecosystems on these soils rely on efficient recycling of nutrients and plant matter by the living plant and microbial biomass to maintain their productivity, a process which is disturbed by human activities. Excessive slope, in particular in the presence of cultivation for the sake of agriculture, may encourage the erosion of the top layer of soil which holds most of the raw organic material that would otherwise eventually become humus.

Plant residue

Typical types and percentages of plant residue components

Cellulose (45%)
Lignin (20%)
Hemicellulose (18%)
Protein (8%)
Sugars and starches (5%)
Fats and waxes (2%)

Cellulose and hemicellulose undergo fast decomposition by fungi and bacteria, with a half-life of 12–18 days in a temperate climate. Brown rot fungi can decompose the cellulose and hemicellulose, leaving the lignin and phenolic compounds behind. Starch, which is an energy storage system for plants, undergoes fast decomposition by bacteria and fungi. Lignin consists of polymers composed of 500 to 600 units with a highly branched, amorphous structure, linked to cellulose, hemicellulose and pectin in plant cell walls. Lignin undergoes very slow decomposition, mainly by white rot fungi and actinomycetes; its half-life under temperate conditions is about six months.

Main article: Soil horizon

A horizontal layer of the soil, whose physical features, composition and age are distinct from those above and beneath, is referred to as a soil horizon. The naming of a horizon is based on the type of material of which it is composed. Those materials reflect the duration of specific processes of soil formation. They are labelled using a shorthand notation of letters and numbers which describe the horizon in terms of its colour, size, texture, structure, consistency, root quantity, pH, voids, boundary characteristics and presence of nodules or concretions. No soil profile has all the major horizons. Some, called entisols, may have only one horizon or are currently considered as having no horizon, in particular incipient soils from unreclaimed mining waste deposits, moraines, volcanic cones sand dunes or alluvial terraces. Upper soil horizons may be lacking in truncated soils following wind or water ablation, with concomitant downslope burying of soil horizons, a natural process aggravated by agricultural practices such as tillage. The growth of trees is another source of disturbance, creating a micro-scale heterogeneity which is still visible in soil horizons once trees have died. By passing from a horizon to another, from the top to the bottom of the soil profile, one goes back in time, with past events registered in soil horizons like in sediment layers. Sampling pollen, testate amoebae and plant remains in soil horizons may help to reveal environmental changes (e.g. climate change, land use change) which occurred in the course of soil formation. Soil horizons can be dated by several methods such as radiocarbon, using pieces of charcoal provided they are of enough size to escape pedoturbation by earthworm activity and other mechanical disturbances. Fossil soil horizons from paleosols can be found within sedimentary rock sequences, allowing the study of past environments.

The exposure of parent material to favourable conditions produces mineral soils that are marginally suitable for plant growth, as is the case in eroded soils. The growth of vegetation results in the production of organic residues which fall on the ground as litter for plant aerial parts (leaf litter) or are directly produced belowground for subterranean plant organs (root litter), and then release dissolved organic matter. The remaining surficial organic layer, called the O horizon, produces a more active soil due to the effect of the organisms that live within it. Organisms colonise and break down organic materials, making available nutrients upon which other plants and animals can live. After sufficient time, humus moves downward and is deposited in a distinctive organic-mineral surface layer called the A horizon, in which organic matter is mixed with mineral matter through the activity of burrowing animals, a process called pedoturbation. This natural process does not go to completion in the presence of conditions detrimental to soil life such as strong acidity, cold climate or pollution, stemming in the accumulation of undecomposed organic matter within a single organic horizon overlying the mineral soil and in the juxtaposition of humified organic matter and mineral particles, without intimate mixing, in the underlying mineral horizons.

Main article: Soil classification

Soil is classified into categories in order to understand relationships between different soils and to determine the suitability of a soil in a particular region. One of the first classification systems was developed by the Russian scientist Vasily Dokuchaev around 1880. It was modified a number of times by American and European researchers, and developed into the system commonly used until the 1960s. It was based on the idea that soils have a particular morphology based on the materials and factors that form them. In the 1960s, a different classification system began to emerge which focused on soil morphology instead of parental materials and soil-forming factors. Since then it has undergone further modifications. The World Reference Base for Soil Resources (WRB) aims to establish an international reference base for soil classification.

Soil is used in agriculture, where it serves as the anchor and primary nutrient base for plants. The types of soil and available moisture determine the species of plants that can be cultivated. Agricultural soil science was the primeval domain of soil knowledge, long time before the advent of pedology in the 19th century. However, as demonstrated by aeroponics, aquaponics and hydroponics, soil material is not an absolute essential for agriculture, and soilless cropping systems have been claimed as the future of agriculture for an endless growing mankind.

Soil material is also a critical component in mining, construction and landscape development industries. Soil serves as a foundation for most construction projects. The movement of massive volumes of soil can be involved in surface mining, road building and dam construction. Earth sheltering is the architectural practice of using soil for external thermal mass against building walls. Many building materials are soil based. Loss of soil through urbanization is growing at a high rate in many areas and can be critical for the maintenance of subsistence agriculture.

Soil resources are critical to the environment, as well as to food and fibre production, producing 98.8% of food consumed by humans. Soil provides minerals and water to plants according to several processes involved in plant nutrition. Soil absorbs rainwater and releases it later, thus preventing floods and drought, flood regulation being one of the major ecosystem services provided by soil. Soil cleans water as it percolates through it. Soil is the habitat for many organisms: the major part of known and unknown biodiversity is in the soil, in the form of earthworms, woodlice, millipedes, centipedes, snails, slugs, mites, springtails, enchytraeids, nematodes, protists), bacteria, archaea, fungi and algae; and most organisms living above ground have part of them (plants) or spend part of their life cycle (insects) below-ground. Above-ground and below-ground biodiversities are tightly interconnected, making soil protection of paramount importance for any restoration or conservation plan.

The biological component of soil is an extremely important carbon sink since about 57% of the biotic content is carbon. Even in deserts, cyanobacteria, lichens and mosses form biological soil crusts which capture and sequester a significant amount of carbon by photosynthesis. Poor farming and grazing methods have degraded soils and released much of this sequestered carbon to the atmosphere. Restoring the world's soils could offset the effect of increases in greenhouse gas emissions and slow global warming, while improving crop yields and reducing water needs.

Waste management often has a soil component. Septic drain fields treat septic tank effluent using aerobic soil processes. Land application of waste water relies on soil biology to aerobically treat BOD. Alternatively, Landfills use soil for daily cover, isolating waste deposits from the atmosphere and preventing unpleasant smells. Composting is now widely used to treat aerobically solid domestic waste and dried effluents of settling basins. Although compost is not soil, biological processes taking place during composting are similar to those occurring during decomposition and humification of soil organic matter.

Organic soils, especially peat, serve as a significant fuel and horticultural resource. Peat soils are also commonly used for the sake of agriculture in Nordic countries, because peatland sites, when drained, provide fertile soils for food production. However, wide areas of peat production, such as rain-fed sphagnum bogs, also called blanket bogs or raised bogs, are now protected because of their patrimonial interest. As an example, Flow Country, covering 4,000 square kilometres of rolling expanse of blanket bogs in Scotland, is now candidate for being included in the World Heritage List. Under present-day global warming peat soils are thought to be involved in a self-reinforcing (positive feedback) process of increased emission of greenhouse gases (methane and carbon dioxide) and increased temperature, a contention which is still under debate when replaced at field scale and including stimulated plant growth.

Geophagy is the practice of eating soil-like substances. Both animals and humans occasionally consume soil for medicinal, recreational, or religious purposes. It has been shown that some monkeys consume soil, together with their preferred food (tree foliage and fruits), in order to alleviate tannin toxicity.

Soils filter and purify water and affect its chemistry. Rain water and pooled water from ponds, lakes and rivers percolate through the soil horizons and the upper rock strata, thus becoming groundwater. Pests (viruses) and pollutants, such as persistent organic pollutants (chlorinated pesticides, polychlorinated biphenyls), oils (hydrocarbons), heavy metals (lead, zinc, cadmium), and excess nutrients (nitrates, sulfates, phosphates) are filtered out by the soil. Soil organisms metabolise them or immobilise them in their biomass and necromass, thereby incorporating them into stable humus. The physical integrity of soil is also a prerequisite for avoiding landslides in rugged landscapes.

Land degradation refers to a human-induced or natural process which impairs the capacity of land to function. Soil degradation involves acidification, contamination, desertification, erosion or salination.

Soil acidification is beneficial in the case of alkaline soils, but it degrades land when it lowers crop productivity, soil biological activity and increases soil vulnerability to contamination and erosion. Soils are initially acid and remain such when their parent materials are low in basic cations (calcium, magnesium, potassium and sodium). On parent materials richer in weatherable minerals acidification occurs when basic cations are leached from the soil profile by rainfall or exported by the harvesting of forest or agricultural crops. Soil acidification is accelerated by the use of acid-forming nitrogenous fertilizers and by the effects of acid precipitation. Deforestation is another cause of soil acidification, mediated by increased leaching of soil nutrients in the absence of tree canopies.

Soil contamination at low levels is often within a soil's capacity to treat and assimilate waste material. Soil biota can treat waste by transforming it, mainly through microbial enzymatic activity. Soil organic matter and soil minerals can adsorb the waste material and decrease its toxicity, although when in colloidal form they may transport the adsorbed contaminants to subsurface environments. Many waste treatment processes rely on this natural bioremediation capacity. Exceeding treatment capacity can damage soil biota and limit soil function. Derelict soils occur where industrial contamination or other development activity damages the soil to such a degree that the land cannot be used safely or productively. Remediation of derelict soil uses principles of geology, physics, chemistry and biology to degrade, attenuate, isolate or remove soil contaminants to restore soil functions and values. Techniques include leaching, air sparging, soil conditioners, phytoremediation, bioremediation and Monitored Natural Attenuation (MNA). An example of diffuse pollution with contaminants is copper accumulation in vineyards and orchards to which fungicides are repeatedly applied, even in organic farming.

Desertification

Desertification is an environmental process of ecosystem degradation in arid and semi-arid regions, often caused by badly adapted human activities such as overgrazing or excess harvesting of firewood. It is a common misconception that drought causes desertification. Droughts are common in arid and semiarid lands. Well-managed lands can recover from drought when the rains return. Soil management tools include maintaining soil nutrient and organic matter levels, reduced tillage and increased cover. These practices help to control erosion and maintain productivity during periods when moisture is available. Continued land abuse during droughts, however, increases land degradation. Increased population and livestock pressure on marginal lands accelerates desertification. It is now questioned whether present-day climate warming will favour or disfavour desertification, with contradictory reports about predicted rainfall trends associated with increased temperature, and strong discrepancies among regions, even in the same country.

Erosion control

Erosion of soil is caused by water, wind, ice, and movement in response to gravity. More than one kind of erosion can occur simultaneously. Erosion is distinguished from weathering, since erosion also transports eroded soil away from its place of origin (soil in transit may be described as sediment). Erosion is an intrinsic natural process, but in many places it is greatly increased by human activity, especially unsuitable land use practices. These include agricultural activities which leave the soil bare during times of heavy rain or strong winds, overgrazing, deforestation, and improper construction activity. Improved management can limit erosion. Soil conservation techniques which are employed include changes of land use (such as replacing erosion-prone crops with grass or other soil-binding plants), changes to the timing or type of agricultural operations, terrace building, use of erosion-suppressing cover materials (including cover crops and other plants), limiting disturbance during construction, and avoiding construction during erosion-prone periods and in erosion-prone places such as steep slopes. Historically, one of the best examples of large-scale soil erosion due to unsuitable land-use practices is wind erosion (the so-called dust bowl) which ruined American and Canadian prairies during the 1930s, when immigrant farmers, encouraged by the federal government of both countries, settled and converted the original shortgrass prairie to agricultural crops and cattle ranching.

A serious and long-running water erosion problem occurs in China, on the middle reaches of the Yellow River and the upper reaches of the Yangtze River. From the Yellow River, over 1.6 billion tons of sediment flow each year into the ocean. The sediment originates primarily from water erosion (gully erosion) in the Loess Plateau region of northwest China.

Soil piping is a particular form of soil erosion that occurs below the soil surface. It causes levee and dam failure, as well as sink hole formation. Turbulent flow removes soil starting at the mouth of the seep flow and the subsoil erosion advances up-gradient. The term sand boil is used to describe the appearance of the discharging end of an active soil pipe.

Soil salination is the accumulation of free salts to such an extent that it leads to degradation of the agricultural value of soils and vegetation. Consequences include corrosion damage, reduced plant growth, erosion due to loss of plant cover and soil structure, and water quality problems due to sedimentation. Salination occurs due to a combination of natural and human-caused processes. Arid conditions favour salt accumulation. This is especially apparent when soil parent material is saline. Irrigation of arid lands is especially problematic. All irrigation water has some level of salinity. Irrigation, especially when it involves leakage from canals and overirrigation in the field, often raises the underlying water table. Rapid salination occurs when the land surface is within the capillary fringe of saline groundwater. Soil salinity control involves watertable control and flushing with higher levels of applied water in combination with tile drainage or another form of subsurface drainage.

Main article: Soil regeneration

Soils which contain high levels of particular clays with high swelling properties, such as smectites, are often very fertile. For example, the smectite-rich paddy soils of Thailand's Central Plains are among the most productive in the world. However, the overuse of mineral nitrogen fertilizers and pesticides in irrigated intensive rice production has endangered these soils, forcing farmers to implement integrated practices based on Cost Reduction Operating Principles (CROP).

Many farmers in tropical areas, however, struggle to retain organic matter and clay in the soils they work. In recent years, for example, productivity has declined and soil erosion has increased in the low-clay soils of northern Thailand, following the abandonment of shifting cultivation for a more permanent land use. Farmers initially responded by adding organic matter and clay from termite mound material, but this was unsustainable in the long-term because of rarefaction of termite mounds. Scientists experimented with adding bentonite, one of the smectite family of clays, to the soil. In field trials, conducted by scientists from the International Water Management Institute in cooperation with Khon Kaen University and local farmers, this had the effect of helping retain water and nutrients. Supplementing the farmer's usual practice with a single application of 200 kg bentonite per rai (6.26 rai = 1 hectare) resulted in an average yield increase of 73%. Other studies showed that applying bentonite to degraded sandy soils reduced the risk of crop failure during drought years.

In 2008, three years after the initial trials, IWMI scientists conducted a survey among 250 farmers in northeast Thailand, half of whom had applied bentonite to their fields. The average improvement for those using the clay addition was 18% higher than for non-clay users. Using the clay had enabled some farmers to switch to growing vegetables, which need more fertile soil. This helped to increase their income. The researchers estimated that 200 farmers in northeast Thailand and 400 in Cambodia had adopted the use of clays, and that a further 20,000 farmers were introduced to the new technique.

If the soil is too high in clay or salts (e.g. saline sodic soil), adding gypsum, washed river sand and organic matter (e.g.municipal solid waste) will balance the composition.

Adding organic matter, like ramial chipped wood or compost, to soil which is depleted in nutrients and too high in sand will boost its quality and improve production.

Special mention must be made of the use of charcoal, and more generally biochar to improve nutrient-poor tropical soils, a process based on the higher fertility of anthropogenic pre-Columbian Amazonian Dark Earths, also called Terra Preta de Índio, due to interesting physical and chemical properties of soil black carbon as a source of stable humus. However, the uncontrolled application of charred waste products of all kinds may endanger soil life and human health.

The history of the study of soil is intimately tied to humans' urgent need to provide food for themselves and forage for their animals. Throughout history, civilizations have prospered or declined as a function of the availability and productivity of their soils.

Studies of soil fertility

Main article: Soil fertility
This section may contain an excessive amount of intricate detail that may interest only a particular audience. Specifically, details could be moved into main article. Please help by spinning off or relocating any relevant information, and removing excessive detail that may be against Wikipedia's inclusion policy.(April 2021) ()

The Greek historian Xenophon (450–355 BCE) is credited with being the first to expound upon the merits of green-manuring crops: "But then whatever weeds are upon the ground, being turned into earth, enrich the soil as much as dung."

Columella's Of husbandry, circa 60 CE, advocated the use of lime and that clover and alfalfa (green manure) should be turned under, and was used by 15 generations (450 years) under the Roman Empire until its collapse. From the fall of Rome to the French Revolution, knowledge of soil and agriculture was passed on from parent to child and as a result, crop yields were low. During the European Middle Ages, Yahya Ibn al-'Awwam's handbook, with its emphasis on irrigation, guided the people of North Africa, Spain and the Middle East; a translation of this work was finally carried to the southwest of the United States when under Spanish influence. Olivier de Serres, considered as the father of French agronomy, was the first to suggest the abandonment of fallowing and its replacement by hay meadows within crop rotations, and he highlighted the importance of soil (the French terroir) in the management of vineyards. His famous book Le Théâtre d'Agriculture et mesnage des champs contributed to the rise of modern, sustainable agriculture and to the collapse of old agricultural practices such as soil amendment for crops by the lifting of forest litter and assarting, which ruined the soils of western Europe during the Middle Ages and even later on according to regions.

Experiments into what made plants grow first led to the idea that the ash left behind when plant matter was burned was the essential element but overlooked the role of nitrogen, which is not left on the ground after combustion, a belief which prevailed until the 19th century. In about 1635, the Flemish chemist Jan Baptist van Helmont thought he had proved water to be the essential element from his famous five years' experiment with a willow tree grown with only the addition of rainwater. His conclusion came from the fact that the increase in the plant's weight had apparently been produced only by the addition of water, with no reduction in the soil's weight. John Woodward (d. 1728) experimented with various types of water ranging from clean to muddy and found muddy water the best, and so he concluded that earthy matter was the essential element. Others concluded it was humus in the soil that passed some essence to the growing plant. Still others held that the vital growth principal was something passed from dead plants or animals to the new plants. At the start of the 18th century, Jethro Tull demonstrated that it was beneficial to cultivate (stir) the soil, but his opinion that the stirring made the fine parts of soil available for plant absorption was erroneous.

As chemistry developed, it was applied to the investigation of soil fertility. The French chemist Antoine Lavoisier showed in about 1778 that plants and animals must [combust] oxygen internally to live and was able to deduce that most of the 165-pound weight of van Helmont's willow tree derived from air. It was the French agriculturalist Jean-Baptiste Boussingault who by means of experimentation obtained evidence showing that the main sources of carbon, hydrogen and oxygen for plants were air and water, while nitrogen was taken from soil. Justus von Liebig in his book Organic chemistry in its applications to agriculture and physiology (published 1840), asserted that the chemicals in plants must have come from the soil and air and that to maintain soil fertility, the used minerals must be replaced. Liebig nevertheless believed the nitrogen was supplied from the air. The enrichment of soil with guano by the Incas was rediscovered in 1802, by Alexander von Humboldt. This led to its mining and that of Chilean nitrate and to its application to soil in the United States and Europe after 1840.

The work of Liebig was a revolution for agriculture, and so other investigators started experimentation based on it. In England John Bennet Lawes and Joseph Henry Gilbert worked in the Rothamsted Experimental Station, founded by the former, and (re)discovered that plants took nitrogen from the soil, and that salts needed to be in an available state to be absorbed by plants. Their investigations also produced the superphosphate, consisting in the acid treatment of phosphate rock. This led to the invention and use of salts of potassium (K) and nitrogen (N) as fertilizers. Ammonia generated by the production of coke was recovered and used as fertiliser. Finally, the chemical basis of nutrients delivered to the soil in manure was understood and in the mid-19th century chemical fertilisers were applied. However, the dynamic interaction of soil and its life forms still awaited discovery.

In 1856 J. Thomas Way discovered that ammonia contained in fertilisers was transformed into nitrates, and twenty years later Robert Warington proved that this transformation was done by living organisms. In 1890 Sergei Winogradsky announced he had found the bacteria responsible for this transformation.

It was known that certain legumes could take up nitrogen from the air and fix it to the soil but it took the development of bacteriology towards the end of the 19th century to lead to an understanding of the role played in nitrogen fixation by bacteria. The symbiosis of bacteria and leguminous roots, and the fixation of nitrogen by the bacteria, were simultaneously discovered by the German agronomist Hermann Hellriegel and the Dutch microbiologist Martinus Beijerinck.

Crop rotation, mechanisation, chemical and natural fertilisers led to a doubling of wheat yields in western Europe between 1800 and 1900.

Studies of soil formation

See also: Pedogenesis

The scientists who studied the soil in connection with agricultural practices had considered it mainly as a static substrate. However, soil is the result of evolution from more ancient geological materials, under the action of biotic and abiotic processes. After studies of the improvement of the soil commenced, other researchers began to study soil genesis and as a result also soil types and classifications.

In 1860, in Mississippi, Eugene W. Hilgard (1833-1916) studied the relationship between rock material, climate, vegetation, and the type of soils that were developed. He realised that the soils were dynamic, and considered the classification of soil types. Unfortunately his work was not continued. At about the same time, Friedrich Albert Fallou was describing soil profiles and relating soil characteristics to their formation as part of his professional work evaluating forest and farm land for the principality of Saxony. His 1857 book, Anfangsgründe der Bodenkunde (First principles of soil science) established modern soil science. Contemporary with Fallou's work, and driven by the same need to accurately assess land for equitable taxation, Vasily Dokuchaev led a team of soil scientists in Russia who conducted an extensive survey of soils, observing that similar basic rocks, climate and vegetation types lead to similar soil layering and types, and established the concepts for soil classifications. Due to language barriers, the work of this team was not communicated to western Europe until 1914 through a publication in German by Konstantin Glinka, a member of the Russian team.

Curtis F. Marbut, influenced by the work of the Russian team, translated Glinka's publication into English, and as he was placed in charge of the U.S. National Cooperative Soil Survey, applied it to a national soil classification system.

Wikimedia Commons has media related toSoils.
Wikiquote has quotations related to: Soil
  1. Chesworth, Ward, ed. (2008). Encyclopedia of soil science(PDF). Dordrecht, The Netherlands: Springer. ISBN 978-1-4020-3994-2. Archived from the original(PDF) on 5 September 2018.
  2. Voroney, R. Paul; Heck, Richard J. (2007). "The soil habitat"(PDF). In Paul, Eldor A. (ed.). Soil microbiology, ecology and biochemistry (3rd ed.). Amsterdam, the Netherlands: Elsevier. pp. 25–49. doi:10.1016/B978-0-08-047514-1.50006-8. ISBN 978-0-12-546807-7. Archived from the original(PDF) on 10 July 2018.
  3. Taylor, Sterling A.; Ashcroft, Gaylen L. (1972).Physical edaphology: the physics of irrigated and nonirrigated soils. San Francisco, California: W.H. Freeman. ISBN 978-0-7167-0818-6.
  4. McCarthy, David F. (2006). Essentials of soil mechanics and foundations: basic geotechnics(PDF) (7th ed.). Upper Saddle River, New Jersey: Prentice Hall. ISBN 978-0-13-114560-3. Retrieved17 January 2021.
  5. Gilluly, James; Waters, Aaron Clement; Woodford, Alfred Oswald (1975). Principles of geology (4th ed.). San Francisco, California: W.H. Freeman. ISBN 978-0-7167-0269-6.
  6. Ponge, Jean-François (2015). "The soil as an ecosystem". Biology and Fertility of Soils. 51 (6): 645–48. doi:10.1007/s00374-015-1016-1. S2CID 18251180. Retrieved24 January 2021.
  7. Yu, Charley; Kamboj, Sunita; Wang, Cheng; Cheng, Jing-Jy (2015). "Data collection handbook to support modeling impacts of radioactive material in soil and building structures"(PDF). Argonne National Laboratory. pp. 13–21. Archived(PDF) from the original on 4 August 2018. Retrieved24 January 2021.
  8. Buol, Stanley W.; Southard, Randal J.; Graham, Robert C.; McDaniel, Paul A. (2011). Soil genesis and classification (7th ed.). Ames, Iowa: Wiley-Blackwell. ISBN 978-0-470-96060-8.
  9. Retallack, Gregory J.; Krinsley, David H.; Fischer, Robert; Razink, Joshua J.; Langworthy, Kurt A. (2016). "Archean coastal-plain paleosols and life on land"(PDF). Gondwana Research. 40: 1–20. Bibcode:2016GondR..40....1R. doi:10.1016/j.gr.2016.08.003. Archived(PDF) from the original on 13 November 2018. Retrieved24 January 2021.
  10. "Glossary of terms in soil science". Agriculture and Agri-Food Canada. 13 December 2013. Archived from the original on 27 October 2018. Retrieved24 January 2021.
  11. Amundson, Ronald. "Soil preservation and the future of pedology"(PDF). Faculty of Natural Resources. Songkhla, Thailand: Prince of Songkla University. Archived(PDF) from the original on 12 June 2018. Retrieved24 January 2021.
  12. Küppers, Michael; Vincent, Jean-Baptiste. "Impacts and formation of regolith". Max Planck Institute for Solar System Research. Archived from the original on 4 August 2018. Retrieved24 January 2021.
  13. Amelung, Wulf; Bossio, Deborah; De Vries, Wim; Kögel-Knabner, Ingrid; Lehmann, Johannes; Amundson, Ronald; Bol, Roland; Collins, Chris; Lal, Rattan; Leifeld, Jens; Minasny, Buniman; Pan, Gen-Xing; Paustian, Keith; Rumpel, Cornelia; Sanderman, Jonathan; Van Groeningen, Jan Willem; Mooney, Siân; Van Wesemael, Bas; Wander, Michelle; Chabbi, Abad (27 October 2020). "Towards a global-scale soil climate mitigation strategy". Nature Communications. 11 (1): 5427. Bibcode:2020NatCo..11.5427A. doi:10.1038/s41467-020-18887-7. ISSN 2041-1723. PMC7591914. PMID 33110065.
  14. Pouyat, Richard; Groffman, Peter; Yesilonis, Ian; Hernandez, Luis (2002). "Soil carbon pools and fluxes in urban ecosystems". Environmental Pollution. 116 (Supplement 1): S107–S118. doi:10.1016/S0269-7491(01)00263-9. PMID 11833898. Retrieved7 February 2021. Our analysis of pedon data from several disturbed soil profiles suggests that physical disturbances and anthropogenic inputs of various materials (direct effects) can greatly alter the amount of C stored in these human "made" soils.
  15. Davidson, Eric A.; Janssens, Ivan A. (2006). "Temperature sensitivity of soil carbon decomposition and feedbacks to climate change"(PDF). Nature. 440 (9 March 2006): 165‒73. Bibcode:2006Natur.440..165D. doi:10.1038/nature04514. PMID 16525463. S2CID 4404915. Retrieved7 February 2021.
  16. Powlson, David (2005). "Will soil amplify climate change?"(PDF). Nature. 433 (20 January 2005): 204‒05. Bibcode:2005Natur.433..204P. doi:10.1038/433204a. PMID 15662396. S2CID 35007042. Retrieved7 February 2021.
  17. Bradford, Mark A.; Wieder, William R.; Bonan, Gordon B.; Fierer, Noah; Raymond, Peter A.; Crowther, Thomas W. (2016). "Managing uncertainty in soil carbon feedbacks to climate change"(PDF). Nature Climate Change. 6 (27 July 2016): 751–58. Bibcode:2016NatCC...6..751B. doi:10.1038/nclimate3071. hdl:20.500.11755/c1792dbf-ce96-4dc7-8851-1ca50a35e5e0. Retrieved7 February 2021.
  18. Dominati, Estelle; Patterson, Murray; Mackay, Alec (2010). "A framework for classifying and quantifying the natural capital and ecosystem services of soils". Ecological Economics. 69 (9): 1858‒68. doi:10.1016/j.ecolecon.2010.05.002. Archived(PDF) from the original on 8 August 2017. Retrieved14 February 2021.
  19. Dykhuizen, Daniel E. (1998). "Santa Rosalia revisited: why are there so many species of bacteria?". Antonie van Leeuwenhoek. 73 (1): 25‒33. doi:10.1023/A:1000665216662. PMID 9602276. S2CID 17779069. Retrieved14 February 2021.
  20. Torsvik, Vigdis; Øvreås, Lise (2002). "Microbial diversity and function in soil: from genes to ecosystems". Current Opinion in Microbiology. 5 (3): 240‒45. doi:10.1016/S1369-5274(02)00324-7. PMID 12057676. Retrieved14 February 2021.
  21. Raynaud, Xavier; Nunan, Naoise (2014). "Spatial ecology of bacteria at the microscale in soil". PLOS ONE. 9 (1): e87217. Bibcode:2014PLoSO...987217R. doi:10.1371/journal.pone.0087217. PMC3905020. PMID 24489873.
  22. Whitman, William B.; Coleman, David C.; Wiebe, William J. (1998). "Prokaryotes: the unseen majority". Proceedings of the National Academy of Sciences of the USA. 95 (12): 6578‒83. Bibcode:1998PNAS...95.6578W. doi:10.1073/pnas.95.12.6578. PMC33863. PMID 9618454.
  23. Schlesinger, William H.; Andrews, Jeffrey A. (2000). "Soil respiration and the global carbon cycle". Biogeochemistry. 48 (1): 7‒20. doi:10.1023/A:1006247623877. S2CID 94252768. Retrieved14 February 2021.
  24. Denmead, Owen Thomas; Shaw, Robert Harold (1962). "Availability of soil water to plants as affected by soil moisture content and meteorological conditions". Agronomy Journal. 54 (5): 385‒90. doi:10.2134/agronj1962.00021962005400050005x. Retrieved14 February 2021.
  25. House, Christopher H.; Bergmann, Ben A.; Stomp, Anne-Marie; Frederick, Douglas J. (1999). "Combining constructed wetlands and aquatic and soil filters for reclamation and reuse of water". Ecological Engineering. 12 (1–2): 27–38. doi:10.1016/S0925-8574(98)00052-4. Retrieved14 February 2021.
  26. Van Bruggen, Ariena H.C.; Semenov, Alexander M. (2000). "In search of biological indicators for soil health and disease suppression". Applied Soil Ecology. 15 (1): 13–24. doi:10.1016/S0929-1393(00)00068-8. Retrieved14 February 2021.
  27. "A citizen's guide to monitored natural attenuation"(PDF). Retrieved14 February 2021.
  28. Linn, Daniel Myron; Doran, John W. (1984). "Effect of water-filled pore space on carbon dioxide and nitrous oxide production in tilled and nontilled soils". Soil Science Society of America Journal. 48 (6): 1267–72. Bibcode:1984SSASJ..48.1267L. doi:10.2136/sssaj1984.03615995004800060013x. Retrieved14 February 2021.
  29. Miller, Raymond W.; Donahue, Roy Luther (1990). Soils: an introduction to soils and plant growth. Upper Saddle River, New Jersey: Prentice Hall. ISBN 978-0-13-820226-2.
  30. Bot, Alexandra; Benites, José (2005). The importance of soil organic matter: key to drought-resistant soil and sustained food and production(PDF). Rome: Food and Agriculture Organization of the United Nations. ISBN 978-92-5-105366-9. Retrieved14 February 2021.
  31. McClellan, Tai. "Soil composition". University of Hawai‘i at Mānoa, College of Tropical Agriculture and Human Resources. Retrieved21 February 2021.
  32. "Arizona Master Gardener Manual". Cooperative Extension, College of Agriculture, University of Arizona. 9 November 2017. Archived from the original on 29 May 2016. Retrieved17 December 2017.
  33. Vannier, Guy (1987). "The porosphere as an ecological medium emphasized in Professor Ghilarov's work on soil animal adaptations"(PDF). Biology and Fertility of Soils. 3 (1): 39–44. doi:10.1007/BF00260577. S2CID 297400. Retrieved21 February 2021.
  34. Torbert, H. Allen; Wood, Wes (1992). "Effect of soil compaction and water-filled pore space on soil microbial activity and N losses". Communications in Soil Science and Plant Analysis. 23 (11): 1321‒31. doi:10.1080/00103629209368668. Retrieved21 February 2021.
  35. Simonson 1957, p. 17.
  36. Zanella, Augusto; Katzensteiner, Klaus; Ponge, Jean-François; Jabiol, Bernard; Sartori, Giacomo; Kolb, Eckart; Le Bayon, Renée-Claire; Aubert, Michaël; Ascher-Jenull, Judith; Englisch, Michael; Hager, Herbert (June 2019). "TerrHum: an iOS App for classifying terrestrial humipedons and some considerations about soil classification". Soil Science Society of America Journal. 83 (S1): S42–S48. doi:10.2136/sssaj2018.07.0279. S2CID 197555747. Retrieved28 February 2021.
  37. Bronick, Carol J.; Lal, Ratan (January 2005). "Soil structure and management: a review"(PDF). Geoderma. 124 (1/2): 3–22. Bibcode:2005Geode.124....3B. doi:10.1016/j.geoderma.2004.03.005. Retrieved21 February 2021.
  38. "Soil and water". Food and Agriculture Organization of the United Nations. Retrieved21 February 2021.
  39. Valentin, Christian; d'Herbès, Jean-Marc; Poesen, Jean (1999). "Soil and water components of banded vegetation patterns". Catena. 37 (1): 1‒24. doi:10.1016/S0341-8162(99)00053-3. Retrieved21 February 2021.
  40. Brady, Nyle C.; Weil, Ray R. (2007). "The colloidal fraction: seat of soil chemical and physical activity". In Brady, Nyle C.; Weil, Ray R. (eds.). The nature and properties of soils (14th ed.). London, United Kingdom: Pearson. pp. 310–57. ISBN 978-0132279383. Retrieved21 February 2021.
  41. "Soil colloids: properties, nature, types and significance"(PDF). Tamil Nadu Agricultural University. Retrieved7 March 2021.
  42. "Cation exchange capacity in soils, simplified". Retrieved7 March 2021.
  43. Miller, Jarrod O. "Soil pH affects nutrient availability"(PDF). University of Maryland. Retrieved7 March 2021.
  44. Goulding, Keith W.T.; Bailey, Neal J.; Bradbury, Nicola J.; Hargreaves, Patrick; Howe, M.T.; Murphy, Daniel V.; Poulton, Paul R.; Willison, Toby W. (1998). "Nitrogen deposition and its contribution to nitrogen cycling and associated soil processes". New Phytologist. 139 (1): 49‒58. doi:10.1046/j.1469-8137.1998.00182.x.
  45. Kononova, M.M. (2013). Soil organic matter: its nature, its role in soil formation and in soil fertility (2nd ed.). Amsterdam, The Netherlands: Elsevier. ISBN 978-1-4831-8568-2.
  46. Burns, Richards G.; DeForest, Jared L.; Marxsen, Jürgen; Sinsabaugh, Robert L.; Stromberger, Mary E.; Wallenstein, Matthew D.; Weintraub, Michael N.; Zoppini, Annamaria (2013). "Soil enzymes in a changing environment: current knowledge and future directions". Soil Biology and Biochemistry. 58: 216‒34. doi:10.1016/j.soilbio.2012.11.009.
  47. Sengupta, Aditi; Kushwaha, Priyanka; Jim, Antonia; Troch, Peter A.; Maier, Raina (2020). "New soil, old plants, and ubiquitous microbes: evaluating the potential of incipient basaltic soil to support native plant growth and influence belowground soil microbial community composition". Sustainability. 12 (10): 4209. doi:10.3390/su12104209.
  48. Bishop, Janice L.; Murchie, Scott L.; Pieters, Carlé L.; Zent, Aaron P. (2002). "A model for formation of dust, soil, and rock coatings on Mars: physical and chemical processes on the Martian surface". Journal of Geophysical Research. 107 (E11): 7-1–7-17. Bibcode:2002JGRE..107.5097B. doi:10.1029/2001JE001581.
  49. Navarro-González, Rafael; Rainey, Fred A.; Molina, Paola; Bagaley, Danielle R.; Hollen, Becky J.; de la Rosa, José; Small, Alanna M.; Quinn, Richard C.; Grunthaner, Frank J.; Cáceres, Luis; Gomez-Silva, Benito; McKay, Christopher P. (2003). "Mars-like soils in the Atacama desert, Chile, and the dry limit of microbial life". Science. 302 (5647): 1018–21. Bibcode:2003Sci...302.1018N. doi:10.1126/science.1089143. PMID 14605363. S2CID 18220447. Retrieved14 March 2021.
  50. Guo, Yong; Fujimura, Reiko; Sato, Yoshinori; Suda, Wataru; Kim, Seok-won; Oshima, Kenshiro; Hattori, Masahira; Kamijo, Takashi; Narisawa, Kazuhiko; Ohta, Hiroyuki (2014). "Characterization of early microbial communities on volcanic deposits along a vegetation gradient on the island of Miyake, Japan". Microbes and Environments. 29 (1): 38–49. doi:10.1264/jsme2.ME13142. PMC4041228. PMID 24463576.
  51. Goldich, Samuel S. (1938). "A study in tock-weathering". The Journal of Geology. 46 (1): 17–58. Bibcode:1938JG.....46...17G. doi:10.1086/624619. ISSN 0022-1376. S2CID 128498195. Retrieved29 September 2021.
  52. Van Schöll, Laura; Smits, Mark M.; Hoffland, Ellis (2006). "Ectomycorrhizal weathering of the soil minerals muscovite and hornblende". New Phytologist. 171 (4): 805–14. doi:10.1111/j.1469-8137.2006.01790.x. PMID 16918551.
  53. Stretch, Rachelle C.; Viles, Heather A. (2002). "The nature and rate of weathering by lichens on lava flows on Lanzarote". Geomorphology. 47 (1): 87–94. Bibcode:2002Geomo..47...87S. doi:10.1016/S0169-555X(02)00143-5. Retrieved21 March 2021.
  54. Dojani, Stephanie; Lakatos, Michael; Rascher, Uwe; Waneck, Wolfgang; Luettge, Ulrich; Büdel, Burkhard (2007). "Nitrogen input by cyanobacterial biofilms of an inselberg into a tropical rainforest in French Guiana". Flora. 202 (7): 521–29. doi:10.1016/j.flora.2006.12.001. Retrieved21 March 2021.
  55. Kabala, Cesary; Kubicz, Justyna (2012). "Initial soil development and carbon accumulation on moraines of the rapidly retreating Werenskiold Glacier, SW Spitsbergen, Svalbard archipelago". Geoderma. 175/176: 9–20. Bibcode:2012Geode.175....9K. doi:10.1016/j.geoderma.2012.01.025. Retrieved26 May 2019.
  56. Jenny, Hans (1941). Factors of soil formation: a system of qunatitative pedology(PDF). New York: McGraw-Hill. Archived(PDF) from the original on 8 August 2017. Retrieved21 March 2021.
  57. Ritter, Michael E. "The physical environment: an introduction to physical geography"(PDF). Retrieved21 March 2021.
  58. Gardner, Catriona M.K.; Laryea, Kofi Buna; Unger, Paul W. (1999). Soil physical constraints to plant growth and crop production(PDF) (1st ed.). Rome: Food and Agriculture Organization of the United Nations. Archived from the original(PDF) on 8 August 2017. Retrieved24 December 2017.
  59. Six, Johan; Paustian, Keith; Elliott, Edward T.; Combrink, Clay (2000). "Soil structure and organic matter. I. Distribution of aggregate-size classes and aggregate-associated carbon". Soil Science Society of America Journal. 64 (2): 681–89. Bibcode:2000SSASJ..64..681S. doi:10.2136/sssaj2000.642681x. Retrieved28 March 2021.
  60. Håkansson, Inge; Lipiec, Jerzy (2000). "A review of the usefulness of relative bulk density values in studies of soil structure and compaction"(PDF). Soil and Tillage Research. 53 (2): 71–85. doi:10.1016/S0167-1987(99)00095-1. S2CID 30045538. Retrieved28 March 2021.
  61. Schwerdtfeger, W.J. (1965). "Soil resistivity as related to underground corrosion and cathodic protection". Journal of Research of the National Bureau of Standards. 69C (1): 71–77. doi:10.6028/jres.069c.012.
  62. Tamboli, Prabhakar Mahadeo (1961). The influence of bulk density and aggregate size on soil moisture retention. Ames, Iowa: Iowa State University. Retrieved28 March 2021.
  63. Qi, Jingen; Marshall, John D.; Mattson, Kim G. (1994). "High soil carbon dioxide concentrations inhibit root respiration of Douglas fir". New Phytologist. 128 (3): 435–42. doi:10.1111/j.1469-8137.1994.tb02989.x. PMID 33874575.
  64. Karberg, Noah J.; Pregitzer, Kurt S.; King, John S.; Friend, Aaron L.; Wood, James R. (2005). "Soil carbon dioxide partial pressure and dissolved inorganic carbonate chemistry under elevated carbon dioxide and ozone"(PDF). Oecologia. 142 (2): 296–306. Bibcode:2005Oecol.142..296K. doi:10.1007/s00442-004-1665-5. PMID 15378342. S2CID 6161016. Retrieved25 April 2021.
  65. Chang, H.T.; Loomis, W.E. (1945). "Effect of carbon dioxide on absorption of water and nutrients by roots". Plant Physiology. 20 (2): 221–32. doi:10.1104/pp.20.2.221. PMC437214. PMID 16653979.
  66. McDowell, Nate J.; Marshall, John D.; Qi, Jingen; Mattson, Kim (1999). "Direct inhibition of maintenance respiration in western hemlock roots exposed to ambient soil carbon dioxide concentrations". Tree Physiology. 19 (9): 599–605. doi:10.1093/treephys/19.9.599. PMID 12651534.
  67. Xu, Xia; Nieber, John L.; Gupta, Satish C. (1992). "Compaction effect on the gas diffusion coefficient in soils". Soil Science Society of America Journal. 56 (6): 1743–50. Bibcode:1992SSASJ..56.1743X. doi:10.2136/sssaj1992.03615995005600060014x. Retrieved25 April 2021.
  68. Smith, Keith A.; Ball, Tom; Conen, Franz; Dobbie, Karen E.; Massheder, Jonathan; Rey, Ana (2003). "Exchange of greenhouse gases between soil and atmosphere: interactions of soil physical factors and biological processes". European Journal of Soil Science. 54 (4): 779–91. doi:10.1046/j.1351-0754.2003.0567.x. S2CID 18442559. Retrieved25 April 2021.
  69. Russell 1957, pp. 35–36.
  70. Ruser, Reiner; Flessa, Heiner; Russow, Rolf; Schmidt, G.; Buegger, Franz; Munch, J.C. (2006). "Emission of N2O, N2 and CO2 from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting". Soil Biology and Biochemistry. 38 (2): 263–74. doi:10.1016/j.soilbio.2005.05.005. Retrieved25 April 2021.
  71. Hartmann, Adrian A.; Buchmann, Nina; Niklaus, Pascal A. (2011). "A study of soil methane sink regulation in two grasslands exposed to drought and N fertilization". Plant and Soil. 342 (1/2): 265–75. doi:10.1007/s11104-010-0690-x. hdl:20.500.11850/34759. S2CID 25691034.
  72. Moore, Tim R.; Dalva, Moshe (1993). "The influence of temperature and water table position on carbon dioxide and methane emissions from laboratory columns of peatland soils". Journal of Soil Science. 44 (4): 651–64. doi:10.1111/j.1365-2389.1993.tb02330.x. Retrieved25 April 2021.
  73. Hiltpold, Ivan; Toepfer, Stefan; Kuhlmann, Ulrich; Turlings, Ted C.J. (2010). "How maize root volatiles affect the efficacy of entomopathogenic nematodes in controlling the western corn rootworm?". Chemoecology. 20 (2): 155–62. doi:10.1007/s00049-009-0034-6. S2CID 30214059. Retrieved2 May 2021.
  74. Ryu, Choong-Min; Farag, Mohamed A.; Hu, Chia-Hui; Reddy, Munagala S.; Wei, Han-Xun; Paré, Paul W.; Kloepper, Joseph W. (2003). "Bacterial volatiles promote growth in Arabidopsis"(PDF). Proceedings of the National Academy of Sciences of the United States of America. 100 (8): 4927–32. Bibcode:2003PNAS..100.4927R. doi:10.1073/pnas.0730845100. PMC153657. PMID 12684534. Retrieved2 May 2021.
  75. Hung, Richard; Lee, Samantha; Bennett, Joan W. (2015). "Fungal volatile organic compounds and their role in ecosystems". Applied Microbiology and Biotechnology. 99 (8): 3395–405. doi:10.1007/s00253-015-6494-4. PMID 25773975. S2CID 14509047. Retrieved2 May 2021.
  76. Purrington, Foster Forbes; Kendall, Paricia A.; Bater, John E.; Stinner, Benjamin R. (1991). "Alarm pheromone in a gregarious poduromorph collembolan (Collembola: Hypogastruridae)". Great Lakes Entomologist. 24 (2): 75–78. Retrieved2 May 2021.
  77. Badri, Dayakar V.; Weir, Tiffany L.; Van der Lelie, Daniel; Vivanco, Jorge M (2009). "Rhizosphere chemical dialogues: plant–microbe interactions"(PDF). Current Opinion in Biotechnology. 20 (6): 642–50. doi:10.1016/j.copbio.2009.09.014. PMID 19875278.
  78. Salmon, Sandrine; Ponge, Jean-François (2001). "Earthworm excreta attract soil springtails: laboratory experiments on Heteromurus nitidus (Collembola: Entomobryidae)". Soil Biology and Biochemistry. 33 (14): 1959–69. doi:10.1016/S0038-0717(01)00129-8. Retrieved2 May 2021.
  79. Lambers, Hans; Mougel, Christophe; Jaillard, Benoît; Hinsinger, Philipe (2009). "Plant-microbe-soil interactions in the rhizosphere: an evolutionary perspective". Plant and Soil. 321 (1/2): 83–115. doi:10.1007/s11104-009-0042-x. S2CID 6840457. Retrieved2 May 2021.
  80. Peñuelas, Josep; Asensio, Dolores; Tholl, Dorothea; Wenke, Katrin; Rosenkranz, Maaria; Piechulla, Birgit; Schnitzler, Jörg-Petter (2014). "Biogenic volatile emissions from the soil". Plant, Cell and Environment. 37 (8): 1866–91. doi:10.1111/pce.12340. PMID 24689847.
  81. Buzuleciu, Samuel A.; Crane, Derek P.; Parker, Scott L. (2016). "Scent of disinterred soil as an olfactory cue used by raccoons to locate nests of diamond-backed terrapins (Malaclemys terrapin)"(PDF). Herpetological Conservation and Biology. 11 (3): 539–51. Retrieved2 May 2021.
  82. Saxton, Keith E.; Rawls, Walter J. (2006). "Soil water characteristic estimates by texture and organic matter for hydrologic solutions"(PDF). Soil Science Society of America Journal. 70 (5): 1569–78. Bibcode:2006SSASJ..70.1569S. CiteSeerX10.1.1.452.9733. doi:10.2136/sssaj2005.0117. S2CID 16826314. Archived(PDF) from the original on 2 September 2018. Retrieved2 May 2021.
  83. College of Tropical Agriculture and Human Resources. "Soil mineralogy". University of Hawaiʻi at Mānoa. Retrieved2 May 2021.
  84. Sposito, Garrison (1984). The surface chemistry of soils. New York, New York: Oxford University Press. Retrieved2 May 2021.
  85. Wynot, Christopher. "Theory of diffusion in colloidal suspensions". Retrieved2 May 2021.
  86. Donahue, Miller & Shickluna 1977, p. 103–06.
  87. Sposito, Garrison; Skipper, Neal T.; Sutton, Rebecca; Park, Sung-Ho; Soper, Alan K.; Greathouse, Jeffery A. (1999). "Surface geochemistry of the clay minerals". Proceedings of the National Academy of Sciences of the United States of America. 96 (7): 3358–64. Bibcode:1999PNAS...96.3358S. doi:10.1073/pnas.96.7.3358. PMC34275. PMID 10097044.
  88. Bickmore, Barry R.; Rosso, Kevin M.; Nagy, Kathryn L.; Cygan, Randall T.; Tadanier, Christopher J. (2003). "Ab initio determination of edge surface structures for dioctahedral 2:1 phyllosilicates: implications for acid-base reactivity"(PDF). Clays and Clay Minerals. 51 (4): 359–71. Bibcode:2003CCM....51..359B. doi:10.1346/CCMN.2003.0510401. S2CID 97428106. Retrieved9 May 2021.
  89. Rajamathi, Michael; Thomas, Grace S.; Kamath, P. Vishnu (2001). "The many ways of making anionic clays". Journal of Chemical Sciences. 113 (5–6): 671–80. doi:10.1007/BF02708799. S2CID 97507578.
  90. Moayedi, Hossein; Kazemian, Sina (2012). "Zeta potentials of suspended humus in multivalent cationic saline solution and its effect on electro-osomosis behavior". Journal of Dispersion Science and Technology. 34 (2): 283–94. doi:10.1080/01932691.2011.646601. S2CID 94333872. Retrieved9 May 2021.
  91. Pettit, Robert E. "Organic matter, humus, humate, humic acid, fulvic acid and humin: their importance in soil fertility and plant health"(PDF). Retrieved16 May 2021.
  92. Diamond, Sidney; Kinter, Earl B. (1965). "Mechanisms of soil-lime stabilization: an interpretive review"(PDF). Highway Research Record. 92: 83–102. Retrieved16 May 2021.
  93. Woodruff, Clarence M. (1955). "The energies of replacement of calcium by potassium in soils"(PDF). Soil Science Society of America Journal. 19 (2): 167–71. Bibcode:1955SSASJ..19..167W. doi:10.2136/sssaj1955.03615995001900020014x. Retrieved16 May 2021.
  94. Fronæus, Sture (1953). "On the application of the mass action law to cation exchange equilibria". Acta Chemica Scandinavica. 7: 469–80. doi:10.3891/acta.chem.scand.07-0469.
  95. Bolland, Mike D. A.; Posner, Alan M.; Quirk, James P. (1980). "pH-independent and pH-dependent surface charges on kaolinite". Clays and Clay Minerals. 28 (6): 412–18. Bibcode:1980CCM....28..412B. CiteSeerX10.1.1.543.8017. doi:10.1346/CCMN.1980.0280602. S2CID 12462516. Retrieved16 May 2021.
  96. Silber, Avner; Levkovitch, Irit; Graber, Ellen R. (2010). "pH-dependent mineral release and surface properties of cornstraw biochar: agronomic implications". Environmental Science and Technology. 44 (24): 9318–23. Bibcode:2010EnST...44.9318S. doi:10.1021/es101283d. PMID 21090742. Retrieved16 May 2021.
  97. Dakora, Felix D.; Phillips, Donald D. (2002). "Root exudates as mediators of mineral acquisition in low-nutrient environments". Plant and Soil. 245: 35–47. doi:10.1023/A:1020809400075. S2CID 3330737. Archived(PDF) from the original on 19 August 2019. Retrieved16 May 2021.
  98. Brown, John C. (1978). "Mechanism of iron uptake by plants". Plant, Cell and Environment. 1 (4): 249–57. doi:10.1111/j.1365-3040.1978.tb02037.x.
  99. Donahue, Miller & Shickluna 1977, p. 114.
  100. Singh, Jamuna Sharan; Raghubanshi, Akhilesh Singh; Singh, Raj S.; Srivastava, S. C. (1989). "Microbial biomass acts as a source of plant nutrient in dry tropical forest and savanna". Nature. 338 (6215): 499–500. Bibcode:1989Natur.338..499S. doi:10.1038/338499a0. S2CID 4301023. Retrieved23 May 2021.
  101. Szatanik-Kloc, Alicja; Szerement, Justyna; Józefaciuk, Grzegorz (2017). "The role of cell walls and pectins in cation exchange and surface area of plant roots". Journal of Plant Physiology. 215: 85–90. doi:10.1016/j.jplph.2017.05.017. PMID 28600926. Retrieved23 May 2021.
  102. Donahue, Miller & Shickluna 1977, pp. 115–16.
  103. Hinsinger, Philippe (2001). "Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review". Plant and Soil. 237 (2): 173–95. doi:10.1023/A:1013351617532.
  104. Gu, Baohua; Schulz, Robert K. (1991). "Anion retention in soil: possible application to reduce migration of buried technetium and iodine, a review". doi:10.2172/5980032.Cite journal requires |journal= ()
  105. Lawrinenko, Michael; Jing, Dapeng; Banik, Chumki; Laird, David A. (2017). "Aluminum and iron biomass pretreatment impacts on biochar anion exchange capacity". Carbon. 118: 422–30. doi:10.1016/j.carbon.2017.03.056.
  106. Sollins, Phillip; Robertson, G. Philip; Uehara, Goro (1988). "Nutrient mobility in variable- and permanent-charge soils"(PDF). Biogeochemistry. 6 (3): 181–99. doi:10.1007/BF02182995. S2CID 4505438.
  107. Sanders, W. M. H. (1964). "Extraction of soil phosphate by anion-exchange membrane". New Zealand Journal of Agricultural Research. 7 (3): 427–31. doi:10.1080/00288233.1964.10416423.
  108. Lawrinenko, Mike; Laird, David A. (2015). "Anion exchange capacity of biochar". Green Chemistry. 17 (9): 4628–36. doi:10.1039/C5GC00828J. Retrieved30 May 2021.
  109. Robertson, Bryan. "pH requirements of freshwater aquatic life"(PDF). Retrieved6 June 2021.
  110. Chang, Raymond, ed. (2010). Chemistry. Chemistry - Chang 12Ed (12th ed.). New York, New York: McGraw-Hill. p. 666. ISBN 9780078021510. Retrieved6 June 2021.
  111. Singleton, Peter L.; Edmeades, Doug C.; Smart, R. E.; Wheeler, David M. (2001). "The many ways of making anionic clays". Journal of Chemical Sciences. 113 (5–6): 671–80. doi:10.1007/BF02708799. S2CID 97507578.
  112. Läuchli, André; Grattan, Steve R. (2012). "Soil pH extremes". In Shabala, Sergey (ed.). Plant stress physiology (1st ed.). Wallingford, United Kingdom: CAB International. pp. 194–209. doi:10.1079/9781845939953.0194. ISBN 978-1845939953. Retrieved13 June 2021.
  113. Donahue, Miller & Shickluna 1977, pp. 116–17.
  114. Calmano, Wolfgang; Hong, Jihua; Förstner, Ulrich (1993). "Binding and mobilization of heavy metals in contaminated sediments affected by pH and redox potential". Water Science and Technology. 28 (8–9): 223–35. doi:10.2166/wst.1993.0622. Retrieved13 June 2021.
  115. Ren, Xiaoya; Zeng, Guangming; Tang, Lin; Wang, Jingjing; Wan, Jia; Liu, Yani; Yu, Jiangfang; Yi, Huan; Ye, Shujing; Deng, Rui (2018). "Sorption, transport and biodegradation: an insight into bioavailability of persistent organic pollutants in soil"(PDF). Science of the Total Environment. 610–611: 1154–63. Bibcode:2018ScTEn.610.1154R. doi:10.1016/j.scitotenv.2017.08.089. PMID 28847136. Retrieved13 June 2021.
  116. Ponge, Jean-François (2003). "Humus forms in terrestrial ecosystems: a framework to biodiversity". Soil Biology and Biochemistry. 35 (7): 935–45. CiteSeerX10.1.1.467.4937. doi:10.1016/S0038-0717(03)00149-4. Retrieved13 June 2021.
  117. Fujii, Kazumichi (2003). "Soil acidification and adaptations of plants and microorganisms in Bornean tropical forests". Ecological Research. 29 (3): 371–81. doi:10.1007/s11284-014-1144-3.
  118. Kauppi, Pekka; Kämäri, Juha; Posch, Maximilian; Kauppi, Lea (1986). "Acidification of forest soils: model development and application for analyzing impacts of acidic deposition in Europe"(PDF). Ecological Modelling. 33 (2–4): 231–53. doi:10.1016/0304-3800(86)90042-6. Retrieved13 June 2021.
  119. Andriesse, Jacobus Pieter (1969). "A study of the environment and characteristics of tropical podzols in Sarawak (East-Malaysia)". Geoderma. 2 (3): 201–27. Bibcode:1969Geode...2..201A. doi:10.1016/0016-7061(69)90038-X. Retrieved13 June 2021.
  120. Rengasamy, Pichu (2006). "World salinization with emphasis on Australia". Journal of Experimental Botany. 57 (5): 1017–23. doi:10.1093/jxb/erj108. PMID 16510516.
  121. Arnon, Daniel I.; Johnson, Clarence M. (1942). "Influence of hydrogen ion concentration on the growth of higher plants under controlled conditions". Plant Physiology. 17 (4): 525–39. doi:10.1104/pp.17.4.525. PMC438054. PMID 16653803.
  122. Chaney, Rufus L.; Brown, John C.; Tiffin, Lee O. (1972). "Obligatory reduction of ferric chelates in iron uptake by soybeans". Plant Physiology. 50 (2): 208–13. doi:10.1104/pp.50.2.208. PMC366111. PMID 16658143.
  123. Donahue, Miller & Shickluna 1977, pp. 116–19.
  124. Ahmad, Sagheer; Ghafoor, Abdul; Qadir, Manzoor; Aziz, M. Abbas (2006). "Amelioration of a calcareous saline-sodic soil by gypsum application and different crop rotations". International Journal of Agriculture and Biology. 8 (2): 142–46. Retrieved13 June 2021.
  125. McFee, William W.; Kelly, J. Michael; Beck, Robert H. (1977). "Acid precipitation effects on soil pH and base saturation of exchange sites". Water, Air, and Soil Pollution. 7 (3): 401–08. Bibcode:1977WASP....7..401M. doi:10.1007/BF00284134.
  126. Farina, Martin Patrick W.; Sumner, Malcolm E.; Plank, C. Owen; Letzsch, W. Stephen (1980). "Exchangeable aluminum and pH as indicators of lime requirement for corn". Soil Science Society of America Journal. 44 (5): 1036–41. Bibcode:1980SSASJ..44.1036F. doi:10.2136/sssaj1980.03615995004400050033x. Retrieved20 June 2021.
  127. Donahue, Miller & Shickluna 1977, pp. 119–20.
  128. Sposito, Garrison; Skipper, Neal T.; Sutton, Rebecca; Park, Sun-Ho; Soper, Alan K.; Greathouse, Jeffery A. (1999). "Surface geochemistry of the clay minerals". Proceedings of the National Academy of Sciences of the United States of America. 96 (7): 3358–64. Bibcode:1999PNAS...96.3358S. doi:10.1073/pnas.96.7.3358. PMC34275. PMID 10097044.
  129. Sparks, Donald L. "Acidic and basic soils: buffering"(PDF). Davis, California: University of California, Davis, Department of Land, Air, and Water Resources. Retrieved20 June 2021.
  130. Ulrich, Bernhard (1983). "Soil acidity and its relations to acid deposition"(PDF). In Ulrich, Bernhard; Pankrath, Jürgen (eds.). Effects of accumulation of air pollutants in forest ecosystems (1st ed.). Dordrecht, The Netherlands: D. Reidel Publishing Company. pp. 127–46. doi:10.1007/978-94-009-6983-4_10. ISBN 978-94-009-6985-8. Retrieved21 June 2021.
  131. Donahue, Miller & Shickluna 1977, pp. 120–21.
  132. Donahue, Miller & Shickluna 1977, p. 125.
  133. Dean 1957, p. 80.
  134. Russel 1957, pp. 123–25.
  135. Brady, Nyle C.; Weil, Ray R. (2008). The nature and properties of soils (15th ed.). Upper Saddle River, New Jersey: Pearson. ISBN 978-0-13-325448-8. Retrieved27 June 2021.
  136. Van der Ploeg, Rienk R.; Böhm, Wolfgang; Kirkham, Mary Beth (1999). "On the origin of the theory of mineral nutrition of plants and the Law of the Minimum". Soil Science Society of America Journal. 63 (5): 1055–62. Bibcode:1999SSASJ..63.1055V. CiteSeerX10.1.1.475.7392. doi:10.2136/sssaj1999.6351055x.
  137. Knecht, Magnus F.; Göransson, Anders (2004). "Terrestrial plants require nutrients in similar proportions". Tree Physiology. 24 (4): 447–60. doi:10.1093/treephys/24.4.447. PMID 14757584.
  138. Dean 1957, pp. 80–81.
  139. Roy, R. N.; Finck, Arnold; Blair, Graeme J.; Tandon, Hari Lal Singh (2006). "Soil fertility and crop production"(PDF). Plant nutrition for food security: a guide for integrated nutrient management. Rome, Italy: Food and Agriculture Organization of the United Nations. pp. 43–90. ISBN 978-92-5-105490-1. Retrieved27 June 2021.
  140. Parfitt, Roger L.; Giltrap, Donna J.; Whitton, Joe S. (1995). "Contribution of organic matter and clay minerals to the cation exchange capacity of soil". Communications in Soil Science and Plant Analysis. 26 (9–10): 1343–55. doi:10.1080/00103629509369376. Retrieved27 June 2021.
  141. Hajnos, Mieczyslaw; Jozefaciuk, Grzegorz; Sokołowska, Zofia; Greiffenhagen, Andreas; Wessolek, Gerd (2003). "Water storage, surface, and structural properties of sandy forest humus horizons". Journal of Plant Nutrition and Soil Science. 166 (5): 625–34. doi:10.1002/jpln.200321161. Retrieved27 June 2021.
  142. Donahue, Miller & Shickluna 1977, pp. 123–31.
  143. Pimentel, David; Harvey, Celia; Resosudarmo, Pradnja; Sinclair, K.; Kurz, D.; McNair, M.; Crist, S.; Shpritz, L.; Fitton, L.; Saffouri, R.; Blair, R. (1995). "Environmental and economic costs of soil erosion and conservation benefits". Science. 267 (5201): 1117–23. Bibcode:1995Sci...267.1117P. doi:10.1126/science.267.5201.1117. PMID 17789193. S2CID 11936877. Archived(PDF) from the original on 13 December 2016. Retrieved4 July 2021.
  144. Schnürer, Johan; Clarholm, Marianne; Rosswall, Thomas (1985). "Microbial biomass and activity in an agricultural soil with different organic matter contents". Soil Biology and Biochemistry. 17 (5): 611–18. doi:10.1016/0038-0717(85)90036-7. Retrieved4 July 2021.
  145. Sparling, Graham P. (1992). "Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter". Australian Journal of Soil Research. 30 (2): 195–207. doi:10.1071/SR9920195. Retrieved4 July 2021.
  146. Varadachari, Chandrika; Ghosh, Kunal (1984). "On humus formation". Plant and Soil. 77 (2): 305–13. doi:10.1007/BF02182933. S2CID 45102095.
  147. Prescott, Cindy E. (2010). "Litter decomposition: what controls it and how can we alter it to sequester more carbon in forest soils?". Biogeochemistry. 101 (1): 133–49. doi:10.1007/s10533-010-9439-0. S2CID 93834812.
  148. Lehmann, Johannes; Kleber, Markus (2015). "The contentious nature of soil organic matter"(PDF). Nature. 528 (7580): 60–68. Bibcode:2015Natur.528...60L. doi:10.1038/nature16069. PMID 26595271. S2CID 205246638. Retrieved4 July 2021.
  149. Piccolo, Alessandro (2002). "The supramolecular structure of humic substances: a novel understanding of humus chemistry and implications in soil science". Advances in Agronomy. 75: 57–134. doi:10.1016/S0065-2113(02)75003-7. ISBN 9780120007936. Retrieved4 July 2021.
  150. Scheu, Stefan (2002). "The soil food web: structure and perspectives". European Journal of Soil Biology. 38 (1): 11–20. doi:10.1016/S1164-5563(01)01117-7. Retrieved4 July 2021.
  151. Foth, Henry D. (1984). Fundamentals of soil science(PDF) (8th ed.). New York, New York: Wiley. p. 139. ISBN 978-0471522799. Retrieved4 July 2021.
  152. Ponge, Jean-François (2003). "Humus forms in terrestrial ecosystems: a framework to biodiversity". Soil Biology and Biochemistry. 35 (7): 935–45. CiteSeerX10.1.1.467.4937. doi:10.1016/S0038-0717(03)00149-4. Archived from the original on 29 January 2016.
  153. Pettit, Robert E. "Organic matter, humus, humate, humic acid, fulvic acid and humin: their importance in soil fertility and plant health"(PDF). Retrieved11 July 2021.
  154. Ji, Rong; Kappler, Andreas; Brune, Andreas (2000). "Transformation and mineralization of synthetic 14C-labeled humic model compounds by soil-feeding termites". Soil Biology and Biochemistry. 32 (8–9): 1281–91. CiteSeerX10.1.1.476.9400. doi:10.1016/S0038-0717(00)00046-8. Retrieved11 July 2021.
  155. Drever, James I.; Vance, George F. (1994). "Role of soil organic acids in mineral weathering processes"(PDF). In Pittman, Edward D.; Lewan, Michael D. (eds.). Organic acids in geological processes. Berlin, Germany: Springer. pp. 138–61. doi:10.1007/978-3-642-78356-2_6. ISBN 978-3-642-78356-2. Retrieved11 July 2021.
  156. Piccolo, Alessandro (1996). "Humus and soil conservation". In Piccolo, Alessandro (ed.). Humic substances in terrestrial ecosystems. Amsterdam, The Netherlands: Elsevier. pp. 225–64. doi:10.1016/B978-044481516-3/50006-2. ISBN 978-0-444-81516-3. Retrieved11 July 2021.
  157. Varadachari, Chandrika; Ghosh, Kunal (1984). "On humus formation". Plant and Soil. 77 (2): 305–13. doi:10.1007/BF02182933. S2CID 45102095. Retrieved11 July 2021.
  158. Mendonça, Eduardo S.; Rowell, David L. (1996). "Mineral and organic fractions of two oxisols and their influence on effective cation-exchange capacity". Soil Science Society of America Journal. 60 (6): 1888–92. Bibcode:1996SSASJ..60.1888M. doi:10.2136/sssaj1996.03615995006000060038x. Retrieved11 July 2021.
  159. Heck, Tobias; Faccio, Greta; Richter, Michael; Thöny-Meyer, Linda (2013). "Enzyme-catalyzed protein crosslinking". Applied Microbiology and Biotechnology. 97 (2): 461–75. doi:10.1007/s00253-012-4569-z. PMC3546294. PMID 23179622. Retrieved11 July 2021.
  160. Lynch, D. L.; Lynch, C. C. (1958). "Resistance of protein–lignin complexes, lignins and humic acids to microbial attack"(PDF). Nature. 181 (4621): 1478–79. Bibcode:1958Natur.181.1478L. doi:10.1038/1811478a0. PMID 13552710. S2CID 4193782. Retrieved11 July 2021.
  161. Dawson, Lorna A.; Hillier, Stephen (2010). "Measurement of soil characteristics for forensic applications"(PDF). Surface and Interface Analysis. 42 (5): 363–77. doi:10.1002/sia.3315. Retrieved18 July 2021.
  162. Manjaiah, K.M.; Kumar, Sarvendra; Sachdev, M. S.; Sachdev, P.; Datta, S. C. (2010). "Study of clay–organic complexes". Current Science. 98 (7): 915–21. Retrieved18 July 2021.
  163. Theng, Benny K.G. (1982). "Clay-polymer interactions: summary and perspectives". Clays and Clay Minerals. 30 (1): 1–10. Bibcode:1982CCM....30....1T. CiteSeerX10.1.1.608.2942. doi:10.1346/CCMN.1982.0300101. S2CID 98176725. Retrieved18 July 2021.
  164. Tietjen, Todd; Wetzel, Robert G. (2003). "Extracellular enzyme-clay mineral complexes: enzyme adsorption, alteration of enzyme activity, and protection from photodegradation"(PDF). Aquatic Ecology. 37 (4): 331–39. doi:10.1023/B:AECO.0000007044.52801.6b. S2CID 6930871. Retrieved18 July 2021.
  165. Tahir, Shermeen; Marschner, Petra (2017). "Clay addition to sandy soil: influence of clay type and size on nutrient availability in sandy soils amended with residues differing in C/N ratio". Pedosphere. 27 (2): 293–305. doi:10.1016/S1002-0160(17)60317-5. Retrieved18 July 2021.
  166. Melero, Sebastiana; Madejón, Engracia; Ruiz, Juan Carlos; Herencia, Juan Francisco (2007). "Chemical and biochemical properties of a clay soil under dryland agriculture system as affected by organic fertilization". European Journal of Agronomy. 26 (3): 327–34. doi:10.1016/j.eja.2006.11.004. Retrieved18 July 2021.
  167. Joanisse, Gilles D.; Bradley, Robert L.; Preston, Caroline M.; Bending, Gary D. (2009). "Sequestration of soil nitrogen as tannin–protein complexes may improve the competitive ability of sheep laurel (Kalmia angustifolia) relative to black spruce (Picea mariana)". New Phytologist. 181 (1): 187–98. doi:10.1111/j.1469-8137.2008.02622.x. PMID 18811620.
  168. Fierer, Noah; Schimel, Joshua P.; Cates, Rex G.; Zou, Jiping (2001). "Influence of balsam poplar tannin fractions on carbon and nitrogen dynamics in Alaskan taiga floodplain soils". Soil Biology and Biochemistry. 33 (12–13): 1827–39. doi:10.1016/S0038-0717(01)00111-0. Retrieved18 July 2021.
  169. Peng, Xinhua; Horn, Rainer (2007). "Anisotropic shrinkage and swelling of some organic and inorganic soils". European Journal of Soil Science. 58 (1): 98–107. doi:10.1111/j.1365-2389.2006.00808.x.
  170. Wang, Yang; Amundson, Ronald; Trumbmore, Susan (1996). "Radiocarbon dating of soil organic matter"(PDF). Quaternary Research. 45 (3): 282–88. Bibcode:1996QuRes..45..282W. doi:10.1006/qres.1996.0029. Retrieved18 July 2021.
  171. Brodowski, Sonja; Amelung, Wulf; Haumaier, Ludwig; Zech, Wolfgang (2007). "Black carbon contribution to stable humus in German arable soils". Geoderma. 139 (1–2): 220–28. Bibcode:2007Geode.139..220B. doi:10.1016/j.geoderma.2007.02.004. Retrieved18 July 2021.
  172. Criscuoli, Irene; Alberti, Giorgio; Baronti, Silvia; Favilli, Filippo; Martinez, Cristina; Calzolari, Costanza; Pusceddu, Emanuela; Rumpel, Cornelia; Viola, Roberto; Miglietta, Franco (2014). "Carbon sequestration and fertility after centennial time scale incorporation of charcoal into soil". PLOS ONE. 9 (3): e91114. Bibcode:2014PLoSO...991114C. doi:10.1371/journal.pone.0091114. PMC3948733. PMID 24614647.
  173. Kim, Dong Jim; Vargas, Rodrigo; Bond-Lamberty, Ben; Turetsky, Merritt R. (2012). "Effects of soil rewetting and thawing on soil gas fluxes: a review of current literature and suggestions for future research". Biogeosciences. 9 (7): 2459-83. Bibcode:2012BGeo....9.2459K. doi:10.5194/bg-9-2459-2012. Retrieved3 October 2021.
  174. Wagai, Rota; Mayer, Lawrence M.; Kitayama, Kanehiro; Knicker, Heike (2008). "Climate and parent material controls on organic matter storage in surface soils: a three-pool, density-separation approach". Geoderma. 147 (1–2): 23–33. Bibcode:2008Geode.147...23W. doi:10.1016/j.geoderma.2008.07.010. hdl:10261/82461. Retrieved25 July 2021.
  175. Minayeva, Tatiana Y.; Trofimov, Sergey Ya.; Chichagova, Olga A.; Dorofeyeva, E. I.; Sirin, Andrey A.; Glushkov, Igor V.; Mikhailov, N. D.; Kromer, Bernd (2008). "Carbon accumulation in soils of forest and bog ecosystems of southern Valdai in the Holocene". Biology Bulletin. 35 (5): 524–32. doi:10.1134/S1062359008050142. S2CID 40927739. Retrieved25 July 2021.
  176. Vitousek, Peter M.; Sanford, Robert L. (1986). "Nutrient cycling in moist tropical forest". Annual Review of Ecology and Systematics. 17: 137–67. doi:10.1146/annurev.es.17.110186.001033. Retrieved25 July 2021.
  177. Rumpel, Cornelia; Chaplot, Vincent; Planchon, Olivier; Bernadou, J.; Valentin, Christian; Mariotti, André (2006). "Preferential erosion of black carbon on steep slopes with slash and burn agriculture". Catena. 65 (1): 30–40. doi:10.1016/j.catena.2005.09.005. Retrieved25 July 2021.
  178. Paul, Eldor A.; Paustian, Keith H.; Elliott, E. T.; Cole, C. Vernon (1997). Soil organic matter in temperate agroecosystems: long-term experiments in North America. Boca Raton, Florida: CRC Press. p. 80. ISBN 978-0-8493-2802-2.
  179. "Horizons". Soils of Canada. Archived from the original on 22 September 2019. Retrieved1 August 2021.
  180. Frouz, Jan; Prach, Karel; Pizl, Václav; Háněl, Ladislav; Starý, Josef; Tajovský, Karel; Materna, Jan; Balík, Vladimír; Kalčík, Jiří; Řehounková, Klára (2008). "Interactions between soil development, vegetation and soil fauna during spontaneous succession in post mining sites". European Journal of Soil Biology. 44 (1): 109–21. doi:10.1016/j.ejsobi.2007.09.002. Retrieved1 August 2021.
  181. Kabala, Cezary; Zapart, Justyna (2012). "Initial soil development and carbon accumulation on moraines of the rapidly retreating Werenskiold Glacier, SW Spitsbergen, Svalbard archipelago". Geoderma. 175–176: 9–20. Bibcode:2012Geode.175....9K. doi:10.1016/j.geoderma.2012.01.025. Retrieved1 August 2021.
  182. Ugolini, Fiorenzo C.; Dahlgren, Randy A. (2002). "Soil development in volcanic ash"(PDF). Global Environmental Research. 6 (2): 69–81. Retrieved1 August 2021.
  183. Huggett, Richard J. (1998). "Soil chronosequences, soil development, and soil evolution: a critical review". Catena. 32 (3): 155–72. doi:10.1016/S0341-8162(98)00053-8. Retrieved1 August 2021.
  184. De Alba, Saturnio; Lindstrom, Michael; Schumacher, Thomas E.; Malo, Douglas D. (2004). "Soil landscape evolution due to soil redistribution by tillage: a new conceptual model of soil catena evolution in agricultural landscapes". Catena. 58 (1): 77–100. doi:10.1016/j.catena.2003.12.004. Retrieved1 August 2021.
  185. Phillips, Jonathan D.; Marion, Daniel A. (2004). "Pedological memory in forest soil development"(PDF). Forest Ecology and Management. 188 (1): 363–80. doi:10.1016/j.foreco.2003.08.007. Retrieved1 August 2021.
  186. Mitchell, Edward A.D.; Van der Knaap, Willem O.; Van Leeuwen, Jacqueline F.N.; Buttler, Alexandre; Warner, Barry G.; Gobat, Jean-Michel (2001). "The palaeoecological history of the Praz-Rodet bog (Swiss Jura) based on pollen, plant macrofossils and testate amoebae(Protozoa)". The Holocene. 11 (1): 65–80. Bibcode:2001Holoc..11...65M. doi:10.1191/095968301671777798. S2CID 131032169. Retrieved1 August 2021.
  187. Carcaillet, Christopher (2001). "Soil particles reworking evidences by AMS 14C dating of charcoal". Comptes Rendus de l'Académie des Sciences, Série IIA. 332 (1): 21–28. doi:10.1016/S1251-8050(00)01485-3. Retrieved1 August 2021.
  188. Retallack, Gregory J. (1991). "Untangling the effects of burial alteration and ancient soil formation". Annual Review of Earth and Planetary Sciences. 19 (1): 183–206. Bibcode:1991AREPS..19..183R. doi:10.1146/annurev.ea.19.050191.001151. Retrieved1 August 2021.
  189. Bakker, Martha M.; Govers, Gerard; Jones, Robert A.; Rounsevell, Mark D.A. (2007). "The effect of soil erosion on Europe's crop yields". Ecosystems. 10 (7): 1209–19. doi:10.1007/s10021-007-9090-3.
  190. Uselman, Shauna M.; Qualls, Robert G.; Lilienfein, Juliane (2007). "Contribution of root vs. leaf litter to dissolved organic carbon leaching through soil". Soil Science Society of America Journal. 71 (5): 1555–63. Bibcode:2007SSASJ..71.1555U. doi:10.2136/sssaj2006.0386. Retrieved8 August 2021.
  191. Schulz, Stefanie; Brankatschk, Robert; Dümig, Alexander; Kögel-Knabner, Ingrid; Schloter, Michae; Zeyer, Josef (2013). "The role of microorganisms at different stages of ecosystem development for soil formation". Biogeosciences. 10 (6): 3983–96. Bibcode:2013BGeo...10.3983S. doi:10.5194/bg-10-3983-2013.
  192. Gillet, Servane; Ponge, Jean-François (2002). "Humus forms and metal pollution in soil". European Journal of Soil Science. 53 (4): 529–39. doi:10.1046/j.1365-2389.2002.00479.x. Retrieved8 August 2021.
  193. Bardy, Marion; Fritsch, Emmanuel; Derenne, Sylvie; Allard, Thierry; do Nascimento, Nadia Régina; Bueno, Guilherme (2008). "Micromorphology and spectroscopic characteristics of organic matter in waterlogged podzols of the upper Amazon basin". Geoderma. 145 (3): 222–30. Bibcode:2008Geode.145..222B. CiteSeerX10.1.1.455.4179. doi:10.1016/j.geoderma.2008.03.008. Retrieved8 August 2021.
  194. Dokuchaev, Vasily Vasilyevich (1967). "Russian Chernozem". Jerusalem, Israel: Israel Program for Scientific Translations. Retrieved15 August 2021.
  195. IUSS Working Group WRB (2015). World Reference Base for Soil Resources 2014: international soil classification system for naming soils and creating legends for soil maps, update 2015(PDF). Rome, Italy: Food and Agriculture Organization. ISBN 978-92-5-108370-3. Retrieved15 August 2021.
  196. AlShrouf, Ali (2017). "Hydroponics, aeroponic and aquaponic as compared with conventional farming". American Scientific Research Journal for Engineering, Technology, and Sciences. 27 (1): 247–55. Retrieved15 August 2021.
  197. Leake, Simon; Haege, Elke (2014). Soils for landscape development: selection, specification and validation. Clayton, Victoria, Australia: CSIRO Publishing. ISBN 978-0643109650.
  198. Pan, Xian-Zhang; Zhao, Qi-Guo (2007). "Measurement of urbanization process and the paddy soil loss in Yixing city, China between 1949 and 2000"(PDF). Catena. 69 (1): 65–73. doi:10.1016/j.catena.2006.04.016. Retrieved15 August 2021.
  199. Kopittke, Peter M.; Menzies, Neal W.; Wang, Peng; McKenna, Brigid A.; Lombi, Enzo (2019). "Soil and the intensification of agriculture for global food security". Environment International. 132: 105078. doi:10.1016/j.envint.2019.105078. ISSN 0160-4120. PMID 31400601.
  200. Stürck, Julia; Poortinga, Ate; Verburg, Peter H. (2014). "Mapping ecosystem services: the supply and demand of flood regulation services in Europe"(PDF). Ecological Indicators. 38: 198–211. doi:10.1016/j.ecolind.2013.11.010. Retrieved15 August 2021.
  201. Van Cuyk, Sheila; Siegrist, Robert; Logan, Andrew; Masson, Sarah; Fischer, Elizabeth; Figueroa, Linda (2001). "Hydraulic and purification behaviors and their interactions during wastewater treatment in soil infiltration systems". Water Research. 35 (4): 953–64. doi:10.1016/S0043-1354(00)00349-3. PMID 11235891. Retrieved15 August 2021.
  202. Jeffery, Simon; Gardi, Ciro; Arwyn, Jones (2010). European atlas of soil biodiversity. Luxembourg, Luxembourg: Publications Office of the European Union. doi:10.2788/94222. ISBN 978-92-79-15806-3. Retrieved15 August 2021.
  203. De Deyn, Gerlinde B.; Van der Putten, Wim H. (2005). "Linking aboveground and belowground diversity". Trends in Ecology and Evolution. 20 (11): 625–33. doi:10.1016/j.tree.2005.08.009. PMID 16701446. Retrieved15 August 2021.
  204. Hansen, James; Sato, Makiko; Kharecha, Pushker; Beerling, David; Berner, Robert; Masson-Delmotte, Valerie; Pagani, Mark; Raymo, Maureen; Royer, Dana L.; Zachos, James C. (2008). "Target atmospheric CO2: where should humanity aim?"(PDF). Open Atmospheric Science Journal. 2 (1): 217–31. arXiv:0804.1126. Bibcode:2008OASJ....2..217H. doi:10.2174/1874282300802010217. S2CID 14890013. Retrieved22 August 2021.
  205. Lal, Rattan (11 June 2004). "Soil carbon sequestration impacts on global climate change and food security"(PDF). Science. 304 (5677): 1623–27. Bibcode:2004Sci...304.1623L. doi:10.1126/science.1097396. PMID 15192216. S2CID 8574723. Retrieved22 August 2021.
  206. Blakeslee, Thomas (24 February 2010). "Greening deserts for carbon credits". Orlando, Florida, USA: Renewable Energy World. Archived from the original on 1 November 2012. Retrieved22 August 2021.
  207. Mondini, Claudio; Contin, Marco; Leita, Liviana; De Nobili, Maria (2002). "Response of microbial biomass to air-drying and rewetting in soils and compost". Geoderma. 105 (1–2): 111–24. Bibcode:2002Geode.105..111M. doi:10.1016/S0016-7061(01)00095-7. Retrieved22 August 2021.
  208. "Peatlands and farming". Stoneleigh, United Kingdom: National Farmers' Union of England and Wales. 6 July 2020. Retrieved22 August 2021.
  209. van Winden, Julia F.; Reichart, Gert-Jan; McNamara, Niall P.; Benthien, Albert; Sinninghe Damste, Jaap S. (2012). "Temperature-induced increase in methane release from peat bogs: a mesocosm experiment". PLoS ONE. 7 (6): e39614. Bibcode:2012PLoSO...739614V. doi:10.1371/journal.pone.0039614. PMC3387254. PMID 22768100.
  210. Davidson, Eric A.; Janssens, Ivan A. (2006). "Temperature sensitivity of soil carbon decomposition and feedbacks to climate change"(PDF). Nature. 440 (7081): 165–73. Bibcode:2006Natur.440..165D. doi:10.1038/nature04514. PMID 16525463. S2CID 4404915. Retrieved22 August 2021.
  211. Abrahams, Pter W. (1997). "Geophagy (soil consumption) and iron supplementation in Uganda". Tropical Medicine and International Health. 2 (7): 617–23. doi:10.1046/j.1365-3156.1997.d01-348.x. PMID 9270729. S2CID 19647911.
  212. Setz, Eleonore Zulnara Freire; Enzweiler, Jacinta; Solferini, Vera Nisaka; Amêndola, Monica Pimenta; Berton, Ronaldo Severiano (1999). "Geophagy in the golden-faced saki monkey (Pithecia pithecia chrysocephala) in the Central Amazon". Journal of Zoology. 247 (1): 91–103. doi:10.1111/j.1469-7998.1999.tb00196.x. Retrieved22 August 2021.
  213. Kohne, John Maximilian; Koehne, Sigrid; Simunek, Jirka (2009). "A review of model applications for structured soils: a) Water flow and tracer transport"(PDF). Journal of Contaminant Hydrology. 104 (1–4): 4–35. Bibcode:2009JCHyd.104....4K. CiteSeerX10.1.1.468.9149. doi:10.1016/j.jconhyd.2008.10.002. PMID 19012994. Archived(PDF) from the original on 7 November 2017. Retrieved22 August 2021.
  214. Diplock, Elizabeth E.; Mardlin, Dave P.; Killham, Kenneth S.; Paton, Graeme Iain (2009). "Predicting bioremediation of hydrocarbons: laboratory to field scale". Environmental Pollution. 157 (6): 1831–40. doi:10.1016/j.envpol.2009.01.022. PMID 19232804. Retrieved22 August 2021.
  215. Moeckel, Claudia; Nizzetto, Luca; Di Guardo, Antonio; Steinnes, Eiliv; Freppaz, Michele; Filippa, Gianluca; Camporini, Paolo; Benner, Jessica; Jones, Kevin C. (2008). "Persistent organic pollutants in boreal and montane soil profiles: distribution, evidence of processes and implications for global cycling". Environmental Science and Technology. 42 (22): 8374–80. Bibcode:2008EnST...42.8374M. doi:10.1021/es801703k. PMID 19068820. Retrieved22 August 2021.
  216. Rezaei, Khalil; Guest, Bernard; Friedrich, Anke; Fayazi, Farajollah; Nakhaei, Mohamad; Aghda, Seyed Mahmoud Fatemi; Beitollahi, Ali (2009). "Soil and sediment quality and composition as factors in the distribution of damage at the December 26, 2003, Bam area earthquake in SE Iran (M (s)=6.6)". Journal of Soils and Sediments. 9: 23–32. doi:10.1007/s11368-008-0046-9. S2CID 129416733. Retrieved22 August 2021.
  217. Johnson, Dan L.; Ambrose, Stanley H.; Bassett, Thomas J.; Bowen, Merle L.; Crummey, Donald E.; Isaacson, John S.; Johnson, David N.; Lamb, Peter; Saul, Mahir; Winter-Nelson, Alex E. (1997). "Meanings of environmental terms". Journal of Environmental Quality. 26 (3): 581–89. doi:10.2134/jeq1997.00472425002600030002x. Retrieved29 August 2021.
  218. Oldeman, L. Roel (1993). "Global extent of soil degradation". ISRIC Bi-Annual Report 1991-1992. Wageningen, The Netherlands: International Soil Reference and Information Centre(ISRIC). pp. 19–36. Retrieved29 August 2021.
  219. Sumner, Malcolm E.; Noble, Andrew D. (2003). "Soil acidification: the world story"(PDF). In Rengel, Zdenko (ed.). Handbook of soil acidity. New York, NY, USA: Marcel Dekker. pp. 1–28. Retrieved29 August 2021.
  220. Karam, Jean; Nicell, James A. (1997). "Potential applications of enzymes in waste treatment". Journal of Chemical Technology & Biotechnology. 69 (2): 141–53. doi:10.1002/(SICI)1097-4660(199706)69:2<141::AID-JCTB694>3.0.CO;2-U. Retrieved5 September 2021.
  221. Sheng, Guangyao; Johnston, Cliff T.; Teppen, Brian J.; Boyd, Stephen A. (2001). "Potential contributions of smectite clays and organic matter to pesticide retention in soils". Journal of Agricultural and Food Chemistry. 49 (6): 2899–2907. doi:10.1021/jf001485d. PMID 11409985. Retrieved5 September 2021.
  222. Sprague, Lori A.; Herman, Janet S.; Hornberger, George M.; Mills, Aaron L. (2000). "Atrazine adsorption and colloid‐facilitated transport through the unsaturated zone"(PDF). Journal of Environmental Quality. 29 (5): 1632–41. doi:10.2134/jeq2000.00472425002900050034x. Retrieved5 September 2021.
  223. Ballabio, Cristiano; Panagos, Panos; Lugato, Emanuele; Huang, Jen-How; Orgiazzi, Alberto; Jones, Arwyn; Fernández-Ugalde, Oihane; Borrelli, Pasquale; Montanarella, Luca (15 September 2018). "Copper distribution in European topsoils: an assessment based on LUCAS soil survey". Science of the Total Environment. 636: 282–98. Bibcode:2018ScTEn.636..282B. doi:10.1016/j.scitotenv.2018.04.268. ISSN 0048-9697. PMID 29709848.
  224. Le Houérou, Henry N. (1996). "Climate change, drought and desertification"(PDF). Journal of Arid Environments. 34 (2): 133–85. Bibcode:1996JArEn..34..133L. doi:10.1006/jare.1996.0099. Retrieved5 September 2021.
  225. Lyu, Yanli; Shi, Peijun; Han, Guoyi; Liu, Lianyou; Guo, Lanlan; Hu, Xia; Zhang, Guoming (2020). "Desertification control practices in China". Sustainability. 12 (8): 3258. doi:10.3390/su12083258. ISSN 2071-1050.
  226. Kéfi, Sonia; Rietkerk, Max; Alados, Concepción L.; Pueyo, Yolanda; Papanastasis, Vasilios P.; El Aich, Ahmed; de Ruiter, Peter C. (2007). "Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems". Nature. 449 (7159): 213–217. Bibcode:2007Natur.449..213K. doi:10.1038/nature06111. hdl:1874/25682. PMID 17851524. S2CID 4411922. Retrieved5 September 2021.
  227. Wang, Xunming; Yang, Yi; Dong, Zhibao; Zhang, Caixia (2009). "Responses of dune activity and desertification in China to global warming in the twenty-first century". Global and Planetary Change. 67 (3–4): 167–85. Bibcode:2009GPC....67..167W. doi:10.1016/j.gloplacha.2009.02.004. Retrieved5 September 2021.
  228. Yang, Dawen; Kanae, Shinjiro; Oki, Taikan; Koike, Toshio; Musiake, Katumi (2003). "Global potential soil erosion with reference to land use and climate changes"(PDF). Hydrological Processes. 17 (14): 2913–28. Bibcode:2003HyPr...17.2913Y. doi:10.1002/hyp.1441. Retrieved5 September 2021.
  229. Sheng, Jian-an; Liao, An-zhong (1997). "Erosion control in South China". Catena. 29 (2): 211–21. doi:10.1016/S0341-8162(96)00057-4. ISSN 0341-8162. Retrieved5 September 2021.
  230. Ran, Lishan; Lu, Xi Xi; Xin, Zhongbao (2014). "Erosion-induced massive organic carbon burial and carbon emission in the Yellow River basin, China"(PDF). Biogeosciences. 11 (4): 945–59. Bibcode:2014BGeo...11..945R. doi:10.5194/bg-11-945-2014. hdl:10722/228184. Retrieved5 September 2021.
  231. Verachtert, Els; Van den Eeckhaut, Miet; Poesen, Jean; Deckers, Jozef (2010). "Factors controlling the spatial distribution of soil piping erosion on loess-derived soils: a case study from central Belgium". Geomorphology. 118 (3): 339–48. Bibcode:2010Geomo.118..339V. doi:10.1016/j.geomorph.2010.02.001. Retrieved5 September 2021.
  232. Jones, Anthony (1976). "Soil piping and stream channel initiation". Water Resources Research. 7 (3): 602–10. Bibcode:1971WRR.....7..602J. doi:10.1029/WR007i003p00602. Retrieved5 September 2021.
  233. Dooley, Alan (June 2006). "Sandboils 101: Corps has experience dealing with common flood danger". Engineer Update. US Army Corps of Engineers. Archived from the original on 18 April 2008.
  234. Oosterbaan, Roland J. (1988). "Effectiveness and social/environmental impacts of irrigation projects: a critical review"(PDF). Annual Reports of the International Institute for Land Reclamation and Improvement (ILRI). Wageningen, The Netherlands. pp. 18–34. Archived(PDF) from the original on 19 February 2009. Retrieved5 September 2021.
  235. Drainage manual: a guide to integrating plant, soil, and water relationships for drainage of irrigated lands(PDF). Washington, D.C.: United States Department of the Interior, Bureau of Reclamation. 1993. ISBN 978-0-16-061623-5. Retrieved5 September 2021.
  236. Oosterbaan, Roland J. "Waterlogging, soil salinity, field irrigation, plant growth, subsurface drainage, groundwater modelling, surface runoff, land reclamation, and other crop production and water management aspects". Archived from the original on 16 August 2010. Retrieved5 September 2021.
  237. Stuart, Alexander M.; Pame, Anny Ruth P.; Vithoonjit, Duangporn; Viriyangkura, Ladda; Pithuncharurnlap, Julmanee; Meesang, Nisa; Suksiri, Prarthana; Singleton, Grant R.; Lampayan, Rubenito M. (2018). "The application of best management practices increases the profitability and sustainability of rice farming in the central plains of Thailand". Field Crops Research. 220: 78–87. doi:10.1016/j.fcr.2017.02.005. RetrievedSoil
Soil Article Talk Language Watch Edit 160 160 Redirected from Soils For other uses see Soil disambiguation Look up soil in Wiktionary the free dictionary Soil is a mixture of organic matter minerals gases liquids and organisms that together support life Earth s body of soil called the pedosphere has four important functions as a medium for plant growth as a means of water storage supply and purification as a modifier of Earth s atmosphere as a habitat for organismsA B and C represent the soil profile a notation firstly coined by Vasily Dokuchaev 1846 1903 the father of pedology A is the topsoil B is a regolith C is a saprolite a less weathered regolith the bottom most layer represents the bedrock Surface water gley developed in glacial till Northern Ireland All of these functions in their turn modify the soil and its properties Soil is also commonly referred to as earth or dirt some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil The pedosphere interfaces with the lithosphere the hydrosphere the atmosphere and the biosphere 1 The term pedolith used commonly to refer to the soil translates to ground stone in the sense fundamental stone from the ancient Greek pedon ground earth Soil consists of a solid phase of minerals and organic matter the soil matrix as well as a porous phase that holds gases the soil atmosphere and water the soil solution 2 3 Accordingly soil scientists can envisage soils as a three state system of solids liquids and gases 4 Soil is a product of several factors the influence of climate relief elevation orientation and slope of terrain organisms and the soil s parent materials original minerals interacting over time 5 It continually undergoes development by way of numerous physical chemical and biological processes which include weathering with associated erosion Given its complexity and strong internal connectedness soil ecologists regard soil as an ecosystem 6 Most soils have a dry bulk density density of soil taking into account voids when dry between 1 1 and 1 6 g cm3 while the soil particle density is much higher in the range of 2 6 to 2 7 g cm3 7 Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic 8 although fossilized soils are preserved from as far back as the Archean 9 Soil science has two basic branches of study edaphology and pedology Edaphology studies the influence of soils on living things 10 Pedology focuses on the formation description morphology and classification of soils in their natural environment 11 In engineering terms soil is included in the broader concept of regolith which also includes other loose material that lies above the bedrock as can be found on the Moon and on other celestial objects 12 Contents 1 Processes 2 Composition 3 Formation 4 Physical properties 5 Soil moisture 6 Soil gas 7 Solid phase soil matrix 8 Chemistry 8 1 Cation and anion exchange 8 1 1 Cation exchange capacity CEC 8 1 2 Anion exchange capacity AEC 8 2 Reactivity pH 8 2 1 Base saturation percentage 8 3 Buffering 9 Nutrients 10 Soil organic matter 10 1 Humus 10 2 Climatological influence 10 3 Plant residue 11 Horizons 12 Classification 13 Uses 14 Degradation 15 Reclamation 16 History of studies and research 16 1 Studies of soil fertility 16 2 Studies of soil formation 17 See also 18 References 19 Bibliography 20 Further reading 21 External linksProcesses EditSoil functions as a major component of the Earth s ecosystem The world s ecosystems are impacted in far reaching ways by the processes carried out in the soil with effects ranging from ozone depletion and global warming to rainforest destruction and water pollution With respect to Earth s carbon cycle soil acts as an important carbon reservoir 13 and it is potentially one of the most reactive to human disturbance 14 and climate change 15 As the planet warms it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures a positive feedback amplification 16 This prediction has however been questioned on consideration of more recent knowledge on soil carbon turnover 17 Soil acts as an engineering medium a habitat for soil organisms a recycling system for nutrients and organic wastes a regulator of water quality a modifier of atmospheric composition and a medium for plant growth making it a critically important provider of ecosystem services 18 Since soil has a tremendous range of available niches and habitats it contains a prominent part of the Earth s genetic diversity A gram of soil can contain billions of organisms belonging to thousands of species mostly microbial and largely still unexplored 19 20 Soil has a mean prokaryotic density of roughly 108 organisms per gram 21 whereas the ocean has no more than 107 prokaryotic organisms per milliliter gram of seawater 22 Organic carbon held in soil is eventually returned to the atmosphere through the process of respiration carried out by heterotrophic organisms but a substantial part is retained in the soil in the form of soil organic matter tillage usually increases the rate of soil respiration leading to the depletion of soil organic matter 23 Since plant roots need oxygen aeration is an important characteristic of soil This ventilation can be accomplished via networks of interconnected soil pores which also absorb and hold rainwater making it readily available for uptake by plants Since plants require a nearly continuous supply of water but most regions receive sporadic rainfall the water holding capacity of soils is vital for plant survival 24 Soils can effectively remove impurities 25 kill disease agents 26 and degrade contaminants this latter property being called natural attenuation 27 Typically soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide 28 Soils offer plants physical support air water temperature moderation nutrients and protection from toxins 29 Soils provide readily available nutrients to plants and animals by converting dead organic matter into various nutrient forms 30 Composition Edit Soil profile Darkened topsoil and reddish subsoil layers are typical of humid subtropical climate regions Components of a silt loam soil by percent volume Water 25 Gases 25 Sand 18 Silt 18 Clay 9 Organic matter 5 A typical soil is about 50 solids 45 mineral and 5 organic matter and 50 voids or pores of which half is occupied by water and half by gas 31 The percent soil mineral and organic content can be treated as a constant in the short term while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other 32 The pore space allows for the infiltration and movement of air and water both of which are critical for life existing in soil 33 Compaction a common problem with soils reduces this space preventing air and water from reaching plant roots and soil organisms 34 Given sufficient time an undifferentiated soil will evolve a soil profile which consists of two or more layers referred to as soil horizons These differ in one or more properties such as in their texture structure density porosity consistency temperature color and reactivity 8 The horizons differ greatly in thickness and generally lack sharp boundaries their development is dependent on the type of parent material the processes that modify those parent materials and the soil forming factors that influence those processes The biological influences on soil properties are strongest near the surface while the geochemical influences on soil properties increase with depth Mature soil profiles typically include three basic master horizons A B and C The solum normally includes the A and B horizons The living component of the soil is largely confined to the solum and is generally more prominent in the A horizon 35 It has been suggested that the pedon a column of soil extending vertically from the surface to the underlying parent material and large enough to show the characteristics of all its horizons could be subdivided in the humipedon the living part where most soil organisms are dwelling corresponding to the humus form the copedon in intermediary position where most weathering of minerals takes place and the lithopedon in contact with the subsoil 36 The soil texture is determined by the relative proportions of the individual particles of sand silt and clay that make up the soil The interaction of the individual mineral particles with organic matter water gases via biotic and abiotic processes causes those particles to flocculate stick together to form aggregates or peds 37 Where these aggregates can be identified a soil can be said to be developed and can be described further in terms of color porosity consistency reaction acidity etc Water is a critical agent in soil development due to its involvement in the dissolution precipitation erosion transport and deposition of the materials of which a soil is composed 38 The mixture of water and dissolved or suspended materials that occupy the soil pore space is called the soil solution Since soil water is never pure water but contains hundreds of dissolved organic and mineral substances it may be more accurately called the soil solution Water is central to the dissolution precipitation and leaching of minerals from the soil profile Finally water affects the type of vegetation that grows in a soil which in turn affects the development of the soil a complex feedback which is exemplified in the dynamics of banded vegetation patterns in semi arid regions 39 Soils supply plants with nutrients most of which are held in place by particles of clay and organic matter colloids 40 The nutrients may be adsorbed on clay mineral surfaces bound within clay minerals absorbed or bound within organic compounds as part of the living organisms or dead soil organic matter These bound nutrients interact with soil water to buffer the soil solution composition attenuate changes in the soil solution as soils wet up or dry out as plants take up nutrients as salts are leached or as acids or alkalis are added 41 42 Plant nutrient availability is affected by soil pH which is a measure of the hydrogen ion activity in the soil solution Soil pH is a function of many soil forming factors and is generally lower more acid where weathering is more advanced 43 Most plant nutrients with the exception of nitrogen originate from the minerals that make up the soil parent material Some nitrogen originates from rain as dilute nitric acid and ammonia 44 but most of the nitrogen is available in soils as a result of nitrogen fixation by bacteria Once in the soil plant system most nutrients are recycled through living organisms plant and microbial residues soil organic matter mineral bound forms and the soil solution Both living soil organisms microbes animals and plant roots and soil organic matter are of critical importance to this recycling and thereby to soil formation and soil fertility 45 Microbial soil enzymes may release nutrients from minerals or organic matter for use by plants and other microorganisms sequester incorporate them into living cells or cause their loss from the soil by volatilisation loss to the atmosphere as gases or leaching 46 Formation EditMain article PedogenesisFurther information Soil mechanics Genesis Soil formation or pedogenesis is the combined effect of physical chemical biological and anthropogenic processes working on soil parent material Soil is said to be formed when organic matter has accumulated and colloids are washed downward leaving deposits of clay humus iron oxide carbonate and gypsum producing a distinct layer called the B horizon This is a somewhat arbitrary definition as mixtures of sand silt clay and humus will support biological and agricultural activity before that time 47 These constituents are moved from one level to another by water and animal activity As a result layers horizons form in the soil profile The alteration and movement of materials within a soil causes the formation of distinctive soil horizons However more recent definitions of soil embrace soils without any organic matter such as those regoliths that formed on Mars 48 and analogous conditions in planet Earth deserts 49 An example of the development of a soil would begin with the weathering of lava flow bedrock which would produce the purely mineral based parent material from which the soil texture forms Soil development would proceed most rapidly from bare rock of recent flows in a warm climate under heavy and frequent rainfall Under such conditions plants in a first stage nitrogen fixing lichens and cyanobacteria then epilithic higher plants become established very quickly on basaltic lava even though there is very little organic material 50 Basaltic minerals commonly weather relatively quickly according to the Goldich dissolution series 51 The plants are supported by the porous rock as it is filled with nutrient bearing water that carries minerals dissolved from the rocks Crevasses and pockets local topography of the rocks would hold fine materials and harbour plant roots The developing plant roots are associated with mineral weathering mycorrhizal fungi 52 that assist in breaking up the porous lava and by these means organic matter and a finer mineral soil accumulate with time Such initial stages of soil development have been described on volcanoes 53 inselbergs 54 and glacial moraines 55 How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil They are parent material climate topography relief organisms and time 56 When reordered to climate relief organisms parent material and time they form the acronym CROPT 57 Physical properties EditMain article Physical properties of soil For the academic discipline see Soil physics The physical properties of soils in order of decreasing importance for ecosystem services such as crop production are texture structure bulk density porosity consistency temperature colour and resistivity 58 Soil texture is determined by the relative proportion of the three kinds of soil mineral particles called soil separates sand silt and clay At the next larger scale soil structures called peds or more commonly soil aggregates are created from the soil separates when iron oxides carbonates clay silica and humus coat particles and cause them to adhere into larger relatively stable secondary structures 59 Soil bulk density when determined at standardized moisture conditions is an estimate of soil compaction 60 Soil porosity consists of the void part of the soil volume and is occupied by gases or water Soil consistency is the ability of soil materials to stick together Soil temperature and colour are self defining Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil 61 These properties vary through the depth of a soil profile i e through soil horizons Most of these properties determine the aeration of the soil and the ability of water to infiltrate and to be held within the soil 62 Soil moisture EditMain article Soil moisture Soil moisture refers to the water content of the soil It can be expressed in terms of volume or weight Soil moisture measurement can be based on in situ probes e g capacitance probes neutron probes or remote sensing methods Soil gas EditMain article Soil gas The atmosphere of soil or soil gas is very different from the atmosphere above The consumption of oxygen by microbes and plant roots and their release of carbon dioxide decrease oxygen and increase carbon dioxide concentration Atmospheric CO2 concentration is 0 04 but in the soil pore space it may range from 10 to 100 times that level thus potentially contributing to the inhibition of root respiration 63 Calcareous soils regulate CO2 concentration by carbonate buffering contrary to acid soils in which all CO2 respired accumulates in the soil pore system 64 At extreme levels CO2 is toxic 65 This suggests a possible negative feedback control of soil CO2 concentration through its inhibitory effects on root and microbial respiration also called soil respiration 66 In addition the soil voids are saturated with water vapour at least until the point of maximal hygroscopicity beyond which a vapour pressure deficit occurs in the soil pore space 33 Adequate porosity is necessary not just to allow the penetration of water but also to allow gases to diffuse in and out Movement of gases is by diffusion from high concentrations to lower the diffusion coefficient decreasing with soil compaction 67 Oxygen from above atmosphere diffuses in the soil where it is consumed and levels of carbon dioxide in excess of above atmosphere diffuse out with other gases including greenhouse gases as well as water 68 Soil texture and structure strongly affect soil porosity and gas diffusion It is the total pore space porosity of soil not the pore size and the degree of pore interconnection or conversely pore sealing together with water content air turbulence and temperature that determine the rate of diffusion of gases into and out of soil 69 68 Platy soil structure and soil compaction low porosity impede gas flow and a deficiency of oxygen may encourage anaerobic bacteria to reduce strip oxygen from nitrate NO3 to the gases N2 N2O and NO which are then lost to the atmosphere thereby depleting the soil of nitrogen a detrimental process called denitrification 70 Aerated soil is also a net sink of methane CH4 71 but a net producer of methane a strong heat absorbing greenhouse gas when soils are depleted of oxygen and subject to elevated temperatures 72 Soil atmosphere is also the seat of emissions of volatiles other than carbon and nitrogen oxides from various soil organisms e g roots 73 bacteria 74 fungi 75 animals 76 These volatiles are used as chemical cues making soil atmosphere the seat of interaction networks 77 78 playing a decisive role in the stability dynamics and evolution of soil ecosystems 79 Biogenic soil volatile organic compounds are exchanged with the aboveground atmosphere in which they are just 1 2 orders of magnitude lower than those from aboveground vegetation 80 Humans can get some idea of the soil atmosphere through the well known after the rain scent when infiltering rainwater flushes out the whole soil atmosphere after a drought period or when soil is excavated 81 a bulk property attributed in a reductionist manner to particular biochemical compounds such as petrichor or geosmin Solid phase soil matrix EditMain article Soil matrix Soil particles can be classified by their chemical composition mineralogy as well as their size The particle size distribution of a soil its texture determines many of the properties of that soil in particular hydraulic conductivity and water potential 82 but the mineralogy of those particles can strongly modify those properties The mineralogy of the finest soil particles clay is especially important 83 Chemistry EditFor the academic discipline see Soil chemistry The chemistry of a soil determines its ability to supply available plant nutrients and affects its physical properties and the health of its living population In addition a soil s chemistry also determines its corrosivity stability and ability to absorb pollutants and to filter water It is the surface chemistry of mineral and organic colloids that determines soil s chemical properties 84 A colloid is a small insoluble particle ranging in size from 1 nanometer to 1 micrometer thus small enough to remain suspended by Brownian motion in a fluid medium without settling 85 Most soils contain organic colloidal particles called humus as well as the inorganic colloidal particles of clays The very high specific surface area of colloids and their net electrical charges give soil its ability to hold and release ions Negatively charged sites on colloids attract and release cations in what is referred to as cation exchange Cation exchange capacity CEC is the amount of exchangeable cations per unit weight of dry soil and is expressed in terms of milliequivalents of positively charged ions per 100 grams of soil or centimoles of positive charge per kilogram of soil cmolc kg Similarly positively charged sites on colloids can attract and release anions in the soil giving the soil anion exchange capacity AEC Cation and anion exchange Edit Further information Cation exchange capacity The cation exchange that takes place between colloids and soil water buffers moderates soil pH alters soil structure and purifies percolating water by adsorbing cations of all types both useful and harmful The negative or positive charges on colloid particles make them able to hold cations or anions respectively to their surfaces The charges result from four sources 86 Isomorphous substitution occurs in clay during its formation when lower valence cations substitute for higher valence cations in the crystal structure 87 Substitutions in the outermost layers are more effective than for the innermost layers as the electric charge strength drops off as the square of the distance The net result is oxygen atoms with net negative charge and the ability to attract cations Edge of clay oxygen atoms are not in balance ionically as the tetrahedral and octahedral structures are incomplete 88 Hydroxyls may substitute for oxygens of the silica layers a process called hydroxylation When the hydrogens of the clay hydroxyls are ionised into solution they leave the oxygen with a negative charge anionic clays 89 Hydrogens of humus hydroxyl groups may also be ionised into solution leaving similarly to clay an oxygen with a negative charge 90 Cations held to the negatively charged colloids resist being washed downward by water and are out of reach of plant roots thereby preserving the fertility of soils in areas of moderate rainfall and low temperatures 91 92 There is a hierarchy in the process of cation exchange on colloids as cations differ in the strength of adsorption by the colloid and hence their ability to replace one another ion exchange If present in equal amounts in the soil water solution Al3 replaces H replaces Ca2 replaces Mg2 replaces K same as NH4 replaces Na 93 If one cation is added in large amounts it may replace the others by the sheer force of its numbers This is called law of mass action This is largely what occurs with the addition of cationic fertilisers potash lime 94 As the soil solution becomes more acidic low pH meaning an abundance of H the other cations more weakly bound to colloids are pushed into solution as hydrogen ions occupy exchange sites protonation A low pH may cause the hydrogen of hydroxyl groups to be pulled into solution leaving charged sites on the colloid available to be occupied by other cations This ionisation of hydroxy groups on the surface of soil colloids creates what is described as pH dependent surface charges 95 Unlike permanent charges developed by isomorphous substitution pH dependent charges are variable and increase with increasing pH 42 Freed cations can be made available to plants but are also prone to be leached from the soil possibly making the soil less fertile 96 Plants are able to excrete H into the soil through the synthesis of organic acids and by that means change the pH of the soil near the root and push cations off the colloids thus making those available to the plant 97 Cation exchange capacity CEC Edit Cation exchange capacity should be thought of as the soil s ability to remove cations from the soil water solution and sequester those to be exchanged later as the plant roots release hydrogen ions to the solution 98 CEC is the amount of exchangeable hydrogen cation H that will combine with 100 grams dry weight of soil and whose measure is one milliequivalents per 100 grams of soil 1 meq 100 g Hydrogen ions have a single charge and one thousandth of a gram of hydrogen ions per 100 grams dry soil gives a measure of one milliequivalent of hydrogen ion Calcium with an atomic weight 40 times that of hydrogen and with a valence of two converts to 40 2 x 1 milliequivalent 20 milliequivalents of hydrogen ion per 100 grams of dry soil or 20 meq 100 g 99 The modern measure of CEC is expressed as centimoles of positive charge per kilogram cmol kg of oven dry soil Most of the soil s CEC occurs on clay and humus colloids and the lack of those in hot humid wet climates e g tropical rainforests due to leaching and decomposition respectively explains the apparent sterility of tropical soils 100 Live plant roots also have some CEC linked to their specific surface area 101 Cation exchange capacity for soils soil textures soil colloids 102 Soil State CEC meq 100 gCharlotte fine sand Florida 1 0Ruston fine sandy loam Texas 1 9Glouchester loam New Jersey 11 9Grundy silt loam Illinois 26 3Gleason clay loam California 31 6Susquehanna clay loam Alabama 34 3Davie mucky fine sand Florida 100 8Sands 1 5Fine sandy loams 5 10Loams and silt loams 5 15Clay loams 15 30Clays over 30Sesquioxides 0 3Kaolinite 3 15Illite 25 40Montmorillonite 60 100Vermiculite similar to illite 80 150Humus 100 300Anion exchange capacity AEC Edit Anion exchange capacity should be thought of as the soil s ability to remove anions e g nitrate phosphate from the soil water solution and sequester those for later exchange as the plant roots release carbonate anions to the soil water solution 103 Those colloids which have low CEC tend to have some AEC Amorphous and sesquioxide clays have the highest AEC 104 followed by the iron oxides 105 Levels of AEC are much lower than for CEC because of the generally higher rate of positively versus negatively charged surfaces on soil colloids to the exception of variable charge soils 106 Phosphates tend to be held at anion exchange sites 107 Iron and aluminum hydroxide clays are able to exchange their hydroxide anions OH for other anions 103 The order reflecting the strength of anion adhesion is as follows H2PO4 replaces SO42 replaces NO3 replaces Cl The amount of exchangeable anions is of a magnitude of tenths to a few milliequivalents per 100 g dry soil 102 As pH rises there are relatively more hydroxyls which will displace anions from the colloids and force them into solution and out of storage hence AEC decreases with increasing pH alkalinity 108 Reactivity pH Edit Main articles Soil pH and Soil pH Effect of soil pH on plant growth Soil reactivity is expressed in terms of pH and is a measure of the acidity or alkalinity of the soil More precisely it is a measure of hydronium concentration in an aqueous solution and ranges in values from 0 to 14 acidic to basic but practically speaking for soils pH ranges from 3 5 to 9 5 as pH values beyond those extremes are toxic to life forms 109 At 25 C an aqueous solution that has a pH of 3 5 has 10 3 5 moles H3O hydronium ions per litre of solution and also 10 10 5 mole litre OH A pH of 7 defined as neutral has 10 7 moles of hydronium ions per litre of solution and also 10 7 moles of OH per litre since the two concentrations are equal they are said to neutralise each other A pH of 9 5 has 10 9 5 moles hydronium ions per litre of solution and also 10 2 5 mole per litre OH A pH of 3 5 has one million times more hydronium ions per litre than a solution with pH of 9 5 9 5 3 5 6 or 106 and is more acidic 110 The effect of pH on a soil is to remove from the soil or to make available certain ions Soils with high acidity tend to have toxic amounts of aluminium and manganese 111 As a result of a trade off between toxicity and requirement most nutrients are better available to plants at moderate pH 112 although most minerals are more soluble in acid soils Soil organisms are hindered by high acidity and most agricultural crops do best with mineral soils of pH 6 5 and organic soils of pH 5 5 113 Given that at low pH toxic metals e g cadmium zinc lead are positively charged as cations and organic pollutants are in non ionic form thus both made more available to organisms 114 115 it has been suggested that plants animals and microbes commonly living in acid soils are pre adapted to every kind of pollution whether of natural or human origin 116 In high rainfall areas soils tend to acidify as the basic cations are forced off the soil colloids by the mass action of hydronium ions from usual or unusual rain acidity against those attached to the colloids High rainfall rates can then wash the nutrients out leaving the soil inhabited only by those organisms which are particularly efficient to uptake nutrients in very acid conditions like in tropical rainforests 117 Once the colloids are saturated with H3O the addition of any more hydronium ions or aluminum hydroxyl cations drives the pH even lower more acidic as the soil has been left with no buffering capacity 118 In areas of extreme rainfall and high temperatures the clay and humus may be washed out further reducing the buffering capacity of the soil 119 In low rainfall areas unleached calcium pushes pH to 8 5 and with the addition of exchangeable sodium soils may reach pH 10 120 Beyond a pH of 9 plant growth is reduced 121 High pH results in low micro nutrient mobility but water soluble chelates of those nutrients can correct the deficit 122 Sodium can be reduced by the addition of gypsum calcium sulphate as calcium adheres to clay more tightly than does sodium causing sodium to be pushed into the soil water solution where it can be washed out by an abundance of water 123 124 Base saturation percentage Edit There are acid forming cations e g hydronium aluminium iron and there are base forming cations e g calcium magnesium sodium The fraction of the negatively charged soil colloid exchange sites CEC that are occupied by base forming cations is called base saturation If a soil has a CEC of 20 meq and 5 meq are aluminium and hydronium cations acid forming the remainder of positions on the colloids 20 5 15 meq are assumed occupied by base forming cations so that the base saturation is 15 20 x 100 75 the compliment 25 is assumed acid forming cations Base saturation is almost in direct proportion to pH it increases with increasing pH 125 It is of use in calculating the amount of lime needed to neutralise an acid soil lime requirement The amount of lime needed to neutralize a soil must take account of the amount of acid forming ions on the colloids exchangeable acidity not just those in the soil water solution free acidity 126 The addition of enough lime to neutralize the soil water solution will be insufficient to change the pH as the acid forming cations stored on the soil colloids will tend to restore the original pH condition as they are pushed off those colloids by the calcium of the added lime 127 Buffering Edit Further information Soil conditioner The resistance of soil to change in pH as a result of the addition of acid or basic material is a measure of the buffering capacity of a soil and for a particular soil type increases as the CEC increases Hence pure sand has almost no buffering ability while soils high in colloids whether mineral or organic have high buffering capacity 128 Buffering occurs by cation exchange and neutralisation However colloids are not the only regulators of soil pH The role of carbonates should be underlined too 129 More generally according to pH levels several buffer systems take precedence over each other from calcium carbonate buffer range to iron buffer range 130 The addition of a small amount of highly basic aqueous ammonia to a soil will cause the ammonium to displace hydronium ions from the colloids and the end product is water and colloidally fixed ammonium but little permanent change overall in soil pH The addition of a small amount of lime Ca OH 2 will displace hydronium ions from the soil colloids causing the fixation of calcium to colloids and the evolution of CO2 and water with little permanent change in soil pH The above are examples of the buffering of soil pH The general principal is that an increase in a particular cation in the soil water solution will cause that cation to be fixed to colloids buffered and a decrease in solution of that cation will cause it to be withdrawn from the colloid and moved into solution buffered The degree of buffering is often related to the CEC of the soil the greater the CEC the greater the buffering capacity of the soil 131 Nutrients EditPlant nutrients their chemical symbols and the ionic forms common in soils and available for plant uptake 132 Element Symbol Ion or moleculeCarbon C CO2 mostly through leaves Hydrogen H H HOH water Oxygen O O2 OH CO32 SO42 CO2Phosphorus P H2PO4 HPO42 phosphates Potassium K K Nitrogen N NH4 NO3 ammonium nitrate Sulfur S SO42 Calcium Ca Ca2 Iron Fe Fe2 Fe3 ferrous ferric Magnesium Mg Mg2 Boron B H3BO3 H2BO3 B OH 4 Manganese Mn Mn2 Copper Cu Cu2 Zinc Zn Zn2 Molybdenum Mo MoO42 molybdate Chlorine Cl Cl chloride Main articles Plant nutrients in soil Plant nutrition and Soil pH Effect of soil pH on plant growth Seventeen elements or nutrients are essential for plant growth and reproduction They are carbon C hydrogen H oxygen O nitrogen N phosphorus P potassium K sulfur S calcium Ca magnesium Mg iron Fe boron B manganese Mn copper Cu zinc Zn molybdenum Mo nickel Ni and chlorine Cl 133 134 135 Nutrients required for plants to complete their life cycle are considered essential nutrients Nutrients that enhance the growth of plants but are not necessary to complete the plant s life cycle are considered non essential With the exception of carbon hydrogen and oxygen which are supplied by carbon dioxide and water and nitrogen provided through nitrogen fixation 135 the nutrients derive originally from the mineral component of the soil The Law of the Minimum expresses that when the available form of a nutrient is not in enough proportion in the soil solution then other nutrients cannot be taken up at an optimum rate by a plant 136 A particular nutrient ratio of the soil solution is thus mandatory for optimizing plant growth a value which might differ from nutrient ratios calculated from plant composition 137 Plant uptake of nutrients can only proceed when they are present in a plant available form In most situations nutrients are absorbed in an ionic form from or together with soil water Although minerals are the origin of most nutrients and the bulk of most nutrient elements in the soil is held in crystalline form within primary and secondary minerals they weather too slowly to support rapid plant growth For example the application of finely ground minerals feldspar and apatite to soil seldom provides the necessary amounts of potassium and phosphorus at a rate sufficient for good plant growth as most of the nutrients remain bound in the crystals of those minerals 138 The nutrients adsorbed onto the surfaces of clay colloids and soil organic matter provide a more accessible reservoir of many plant nutrients e g K Ca Mg P Zn As plants absorb the nutrients from the soil water the soluble pool is replenished from the surface bound pool The decomposition of soil organic matter by microorganisms is another mechanism whereby the soluble pool of nutrients is replenished this is important for the supply of plant available N S P and B from soil 139 Gram for gram the capacity of humus to hold nutrients and water is far greater than that of clay minerals most of the soil cation exchange capacity arising from charged carboxylic groups on organic matter 140 However despite the great capacity of humus to retain water once water soaked its high hydrophobicity decreases its wettability 141 All in all small amounts of humus may remarkably increase the soil s capacity to promote plant growth 142 139 Soil organic matter EditMain article Soil organic matterThis section may contain an excessive amount of intricate detail that may interest only a particular audience Specifically details could be moved into main article Please help by spinning off or relocating any relevant information and removing excessive detail that may be against Wikipedia s inclusion policy April 2021 Learn how and when to remove this template message Soil organic matter is made up of organic compounds and includes plant animal and microbial material both living and dead A typical soil has a biomass composition of 70 microorganisms 22 macrofauna and 8 roots The living component of an acre of soil may include 900 lb of earthworms 2400 lb of fungi 1500 lb of bacteria 133 lb of protozoa and 890 lb of arthropods and algae 143 A few percent of the soil organic matter with small residence time consists of the microbial biomass and metabolites of bacteria molds and actinomycetes that work to break down the dead organic matter 144 145 Were it not for the action of these micro organisms the entire carbon dioxide part of the atmosphere would be sequestered as organic matter in the soil However in the same time soil microbes contribute to carbon sequestration in the topsoil through the formation of stable humus 146 In the aim to sequester more carbon in the soil for alleviating the greenhouse effect it would be more efficient in the long term to stimulate humification than to decrease litter decomposition 147 The main part of soil organic matter is a complex assemblage of small organic molecules collectively called humus or humic substances The use of these terms which do not rely on a clear chemical classification has been considered as obsolete 148 Other studies showed that the classical notion of molecule is not convenient for humus which escaped most attempts done over two centuries to resolve it in unit components but still is chemically distinct from polysaccharides lignins and proteins 149 Most living things in soils including plants animals bacteria and fungi are dependent on organic matter for nutrients and or energy Soils have organic compounds in varying degrees of decomposition which rate is dependent on temperature soil moisture and aeration Bacteria and fungi feed on the raw organic matter which are fed upon by protozoa which in turn are fed upon by nematodes annelids and arthropods themselves able to consume and transform raw or humified organic matter This has been called the soil food web through which all organic matter is processed as in a digestive system 150 Organic matter holds soils open allowing the infiltration of air and water and may hold as much as twice its weight in water Many soils including desert and rocky gravel soils have little or no organic matter Soils that are all organic matter such as peat histosols are infertile 151 In its earliest stage of decomposition the original organic material is often called raw organic matter The final stage of decomposition is called humus In grassland much of the organic matter added to the soil is from the deep fibrous grass root systems By contrast tree leaves falling on the forest floor are the principal source of soil organic matter in the forest Another difference is the frequent occurrence in the grasslands of fires that destroy large amounts of aboveground material but stimulate even greater contributions from roots Also the much greater acidity under any forests inhibits the action of certain soil organisms that otherwise would mix much of the surface litter into the mineral soil As a result the soils under grasslands generally develop a thicker A horizon with a deeper distribution of organic matter than in comparable soils under forests which characteristically store most of their organic matter in the forest floor O horizon and thin A horizon 152 Humus Edit Humus refers to organic matter that has been decomposed by soil microflora and fauna to the point where it is resistant to further breakdown Humus usually constitutes only five percent of the soil or less by volume but it is an essential source of nutrients and adds important textural qualities crucial to soil health and plant growth 153 Humus also feeds arthropods termites and earthworms which further improve the soil 154 The end product humus is suspended in colloidal form in the soil solution and forms a weak acid that can attack silicate minerals by chelating their iron and aluminum atoms 155 Humus has a high cation and anion exchange capacity that on a dry weight basis is many times greater than that of clay colloids It also acts as a buffer like clay against changes in pH and soil moisture 156 Humic acids and fulvic acids which begin as raw organic matter are important constituents of humus After the death of plants animals and microbes microbes begin to feed on the residues through their production of extra cellular soil enzymes resulting finally in the formation of humus 157 As the residues break down only molecules made of aliphatic and aromatic hydrocarbons assembled and stabilized by oxygen and hydrogen bonds remain in the form of complex molecular assemblages collectively called humus 149 Humus is never pure in the soil because it reacts with metals and clays to form complexes which further contribute to its stability and to soil structure 156 While the structure of humus has in itself few nutrients with the exception of constitutive metals such as calcium iron and aluminum it is able to attract and link by weak bonds cation and anion nutrients that can further be released into the soil solution in response to selective root uptake and changes in soil pH a process of paramount importance for the maintenance of fertility in tropical soils 158 Lignin is resistant to breakdown and accumulates within the soil It also reacts with proteins 159 which further increases its resistance to decomposition including enzymatic decomposition by microbes 160 Fats and waxes from plant matter have still more resistance to decomposition and persist in soils for thousand years hence their use as tracers of past vegetation in buried soil layers 161 Clay soils often have higher organic contents that persist longer than soils without clay as the organic molecules adhere to and are stabilised by the clay 162 Proteins normally decompose readily to the exception of scleroproteins but when bound to clay particles they become more resistant to decomposition 163 As for other proteins clay particles absorb the enzymes exuded by microbes decreasing enzyme activity while protecting extracellular enzymes from degradation 164 The addition of organic matter to clay soils can render that organic matter and any added nutrients inaccessible to plants and microbes for many years 165 while a study showed increased soil fertility following the addition of mature compost to a clay soil 166 High soil tannin content can cause nitrogen to be sequestered as resistant tannin protein complexes 167 168 Humus formation is a process dependent on the amount of plant material added each year and the type of base soil Both are affected by climate and the type of organisms present 152 Soils with humus can vary in nitrogen content but typically have 3 to 6 percent nitrogen Raw organic matter as a reserve of nitrogen and phosphorus is a vital component affecting soil fertility 151 Humus also absorbs water and expands and shrinks between dry and wet states to a higher extent than clay increasing soil porosity 169 Humus is less stable than the soil s mineral constituents as it is reduced by microbial decomposition and over time its concentration diminishes without the addition of new organic matter However humus in its most stable forms may persist over centuries if not millennia 170 Charcoal is a source of highly stable humus called black carbon 171 which had been used traditionally to improve the fertility of nutrient poor tropical soils This very ancient practice as ascertained in the genesis of Amazonian dark earths has been renewed and became popular under the name of biochar It has been suggested that biochar could be used to sequester more carbon in the fight against the greenhouse effect 172 Climatological influence Edit The production accumulation and degradation of organic matter are greatly dependent on climate For example when a thawing event occurs the flux of soil gases with atmospheric gases is significantly influenced 173 Temperature soil moisture and topography are the major factors affecting the accumulation of organic matter in soils Organic matter tends to accumulate under wet or cold conditions where decomposer activity is impeded by low temperature 174 or excess moisture which results in anaerobic conditions 175 Conversely excessive rain and high temperatures of tropical climates enables rapid decomposition of organic matter and leaching of plant nutrients Forest ecosystems on these soils rely on efficient recycling of nutrients and plant matter by the living plant and microbial biomass to maintain their productivity a process which is disturbed by human activities 176 Excessive slope in particular in the presence of cultivation for the sake of agriculture may encourage the erosion of the top layer of soil which holds most of the raw organic material that would otherwise eventually become humus 177 Plant residue Edit Typical types and percentages of plant residue components Cellulose 45 Lignin 20 Hemicellulose 18 Protein 8 Sugars and starches 5 Fats and waxes 2 Cellulose and hemicellulose undergo fast decomposition by fungi and bacteria with a half life of 12 18 days in a temperate climate 178 Brown rot fungi can decompose the cellulose and hemicellulose leaving the lignin and phenolic compounds behind Starch which is an energy storage system for plants undergoes fast decomposition by bacteria and fungi Lignin consists of polymers composed of 500 to 600 units with a highly branched amorphous structure linked to cellulose hemicellulose and pectin in plant cell walls Lignin undergoes very slow decomposition mainly by white rot fungi and actinomycetes its half life under temperate conditions is about six months 178 Horizons EditMain article Soil horizon A horizontal layer of the soil whose physical features composition and age are distinct from those above and beneath is referred to as a soil horizon The naming of a horizon is based on the type of material of which it is composed Those materials reflect the duration of specific processes of soil formation They are labelled using a shorthand notation of letters and numbers which describe the horizon in terms of its colour size texture structure consistency root quantity pH voids boundary characteristics and presence of nodules or concretions 179 No soil profile has all the major horizons Some called entisols may have only one horizon or are currently considered as having no horizon in particular incipient soils from unreclaimed mining waste deposits 180 moraines 181 volcanic cones 182 sand dunes or alluvial terraces 183 Upper soil horizons may be lacking in truncated soils following wind or water ablation with concomitant downslope burying of soil horizons a natural process aggravated by agricultural practices such as tillage 184 The growth of trees is another source of disturbance creating a micro scale heterogeneity which is still visible in soil horizons once trees have died 185 By passing from a horizon to another from the top to the bottom of the soil profile one goes back in time with past events registered in soil horizons like in sediment layers Sampling pollen testate amoebae and plant remains in soil horizons may help to reveal environmental changes e g climate change land use change which occurred in the course of soil formation 186 Soil horizons can be dated by several methods such as radiocarbon using pieces of charcoal provided they are of enough size to escape pedoturbation by earthworm activity and other mechanical disturbances 187 Fossil soil horizons from paleosols can be found within sedimentary rock sequences allowing the study of past environments 188 The exposure of parent material to favourable conditions produces mineral soils that are marginally suitable for plant growth as is the case in eroded soils 189 The growth of vegetation results in the production of organic residues which fall on the ground as litter for plant aerial parts leaf litter or are directly produced belowground for subterranean plant organs root litter and then release dissolved organic matter 190 The remaining surficial organic layer called the O horizon produces a more active soil due to the effect of the organisms that live within it Organisms colonise and break down organic materials making available nutrients upon which other plants and animals can live 191 After sufficient time humus moves downward and is deposited in a distinctive organic mineral surface layer called the A horizon in which organic matter is mixed with mineral matter through the activity of burrowing animals a process called pedoturbation This natural process does not go to completion in the presence of conditions detrimental to soil life such as strong acidity cold climate or pollution stemming in the accumulation of undecomposed organic matter within a single organic horizon overlying the mineral soil 192 and in the juxtaposition of humified organic matter and mineral particles without intimate mixing in the underlying mineral horizons 193 Classification EditMain article Soil classification Soil is classified into categories in order to understand relationships between different soils and to determine the suitability of a soil in a particular region One of the first classification systems was developed by the Russian scientist Vasily Dokuchaev around 1880 194 It was modified a number of times by American and European researchers and developed into the system commonly used until the 1960s It was based on the idea that soils have a particular morphology based on the materials and factors that form them In the 1960s a different classification system began to emerge which focused on soil morphology instead of parental materials and soil forming factors Since then it has undergone further modifications The World Reference Base for Soil Resources WRB 195 aims to establish an international reference base for soil classification Uses EditSoil is used in agriculture where it serves as the anchor and primary nutrient base for plants The types of soil and available moisture determine the species of plants that can be cultivated Agricultural soil science was the primeval domain of soil knowledge long time before the advent of pedology in the 19th century However as demonstrated by aeroponics aquaponics and hydroponics soil material is not an absolute essential for agriculture and soilless cropping systems have been claimed as the future of agriculture for an endless growing mankind 196 Soil material is also a critical component in mining construction and landscape development industries 197 Soil serves as a foundation for most construction projects The movement of massive volumes of soil can be involved in surface mining road building and dam construction Earth sheltering is the architectural practice of using soil for external thermal mass against building walls Many building materials are soil based Loss of soil through urbanization is growing at a high rate in many areas and can be critical for the maintenance of subsistence agriculture 198 Soil resources are critical to the environment as well as to food and fibre production producing 98 8 of food consumed by humans 199 Soil provides minerals and water to plants according to several processes involved in plant nutrition Soil absorbs rainwater and releases it later thus preventing floods and drought flood regulation being one of the major ecosystem services provided by soil 200 Soil cleans water as it percolates through it 201 Soil is the habitat for many organisms the major part of known and unknown biodiversity is in the soil in the form of earthworms woodlice millipedes centipedes snails slugs mites springtails enchytraeids nematodes protists bacteria archaea fungi and algae and most organisms living above ground have part of them plants or spend part of their life cycle insects below ground 202 Above ground and below ground biodiversities are tightly interconnected 152 203 making soil protection of paramount importance for any restoration or conservation plan The biological component of soil is an extremely important carbon sink since about 57 of the biotic content is carbon Even in deserts cyanobacteria lichens and mosses form biological soil crusts which capture and sequester a significant amount of carbon by photosynthesis Poor farming and grazing methods have degraded soils and released much of this sequestered carbon to the atmosphere Restoring the world s soils could offset the effect of increases in greenhouse gas emissions and slow global warming while improving crop yields and reducing water needs 204 205 206 Waste management often has a soil component Septic drain fields treat septic tank effluent using aerobic soil processes Land application of waste water relies on soil biology to aerobically treat BOD Alternatively Landfills use soil for daily cover isolating waste deposits from the atmosphere and preventing unpleasant smells Composting is now widely used to treat aerobically solid domestic waste and dried effluents of settling basins Although compost is not soil biological processes taking place during composting are similar to those occurring during decomposition and humification of soil organic matter 207 Organic soils especially peat serve as a significant fuel and horticultural resource Peat soils are also commonly used for the sake of agriculture in Nordic countries because peatland sites when drained provide fertile soils for food production 208 However wide areas of peat production such as rain fed sphagnum bogs also called blanket bogs or raised bogs are now protected because of their patrimonial interest As an example Flow Country covering 4 000 square kilometres of rolling expanse of blanket bogs in Scotland is now candidate for being included in the World Heritage List Under present day global warming peat soils are thought to be involved in a self reinforcing positive feedback process of increased emission of greenhouse gases methane and carbon dioxide and increased temperature 209 a contention which is still under debate when replaced at field scale and including stimulated plant growth 210 Geophagy is the practice of eating soil like substances Both animals and humans occasionally consume soil for medicinal recreational or religious purposes 211 It has been shown that some monkeys consume soil together with their preferred food tree foliage and fruits in order to alleviate tannin toxicity 212 Soils filter and purify water and affect its chemistry Rain water and pooled water from ponds lakes and rivers percolate through the soil horizons and the upper rock strata thus becoming groundwater Pests viruses and pollutants such as persistent organic pollutants chlorinated pesticides polychlorinated biphenyls oils hydrocarbons heavy metals lead zinc cadmium and excess nutrients nitrates sulfates phosphates are filtered out by the soil 213 Soil organisms metabolise them or immobilise them in their biomass and necromass 214 thereby incorporating them into stable humus 215 The physical integrity of soil is also a prerequisite for avoiding landslides in rugged landscapes 216 Degradation EditMain articles Soil retrogression and degradation and Soil conservation Land degradation refers to a human induced or natural process which impairs the capacity of land to function 217 Soil degradation involves acidification contamination desertification erosion or salination 218 Soil acidification is beneficial in the case of alkaline soils but it degrades land when it lowers crop productivity soil biological activity and increases soil vulnerability to contamination and erosion Soils are initially acid and remain such when their parent materials are low in basic cations calcium magnesium potassium and sodium On parent materials richer in weatherable minerals acidification occurs when basic cations are leached from the soil profile by rainfall or exported by the harvesting of forest or agricultural crops Soil acidification is accelerated by the use of acid forming nitrogenous fertilizers and by the effects of acid precipitation Deforestation is another cause of soil acidification mediated by increased leaching of soil nutrients in the absence of tree canopies 219 Soil contamination at low levels is often within a soil s capacity to treat and assimilate waste material Soil biota can treat waste by transforming it mainly through microbial enzymatic activity 220 Soil organic matter and soil minerals can adsorb the waste material and decrease its toxicity 221 although when in colloidal form they may transport the adsorbed contaminants to subsurface environments 222 Many waste treatment processes rely on this natural bioremediation capacity Exceeding treatment capacity can damage soil biota and limit soil function Derelict soils occur where industrial contamination or other development activity damages the soil to such a degree that the land cannot be used safely or productively Remediation of derelict soil uses principles of geology physics chemistry and biology to degrade attenuate isolate or remove soil contaminants to restore soil functions and values Techniques include leaching air sparging soil conditioners phytoremediation bioremediation and Monitored Natural Attenuation MNA An example of diffuse pollution with contaminants is copper accumulation in vineyards and orchards to which fungicides are repeatedly applied even in organic farming 223 Desertification Desertification is an environmental process of ecosystem degradation in arid and semi arid regions often caused by badly adapted human activities such as overgrazing or excess harvesting of firewood It is a common misconception that drought causes desertification 224 Droughts are common in arid and semiarid lands Well managed lands can recover from drought when the rains return Soil management tools include maintaining soil nutrient and organic matter levels reduced tillage and increased cover 225 These practices help to control erosion and maintain productivity during periods when moisture is available Continued land abuse during droughts however increases land degradation Increased population and livestock pressure on marginal lands accelerates desertification 226 It is now questioned whether present day climate warming will favour or disfavour desertification with contradictory reports about predicted rainfall trends associated with increased temperature and strong discrepancies among regions even in the same country 227 Erosion control Erosion of soil is caused by water wind ice and movement in response to gravity More than one kind of erosion can occur simultaneously Erosion is distinguished from weathering since erosion also transports eroded soil away from its place of origin soil in transit may be described as sediment Erosion is an intrinsic natural process but in many places it is greatly increased by human activity especially unsuitable land use practices 228 These include agricultural activities which leave the soil bare during times of heavy rain or strong winds overgrazing deforestation and improper construction activity Improved management can limit erosion Soil conservation techniques which are employed include changes of land use such as replacing erosion prone crops with grass or other soil binding plants changes to the timing or type of agricultural operations terrace building use of erosion suppressing cover materials including cover crops and other plants limiting disturbance during construction and avoiding construction during erosion prone periods and in erosion prone places such as steep slopes 229 Historically one of the best examples of large scale soil erosion due to unsuitable land use practices is wind erosion the so called dust bowl which ruined American and Canadian prairies during the 1930s when immigrant farmers encouraged by the federal government of both countries settled and converted the original shortgrass prairie to agricultural crops and cattle ranching A serious and long running water erosion problem occurs in China on the middle reaches of the Yellow River and the upper reaches of the Yangtze River From the Yellow River over 1 6 billion tons of sediment flow each year into the ocean The sediment originates primarily from water erosion gully erosion in the Loess Plateau region of northwest China 230 Soil piping is a particular form of soil erosion that occurs below the soil surface 231 It causes levee and dam failure as well as sink hole formation Turbulent flow removes soil starting at the mouth of the seep flow and the subsoil erosion advances up gradient 232 The term sand boil is used to describe the appearance of the discharging end of an active soil pipe 233 Soil salination is the accumulation of free salts to such an extent that it leads to degradation of the agricultural value of soils and vegetation Consequences include corrosion damage reduced plant growth erosion due to loss of plant cover and soil structure and water quality problems due to sedimentation Salination occurs due to a combination of natural and human caused processes Arid conditions favour salt accumulation This is especially apparent when soil parent material is saline Irrigation of arid lands is especially problematic 234 All irrigation water has some level of salinity Irrigation especially when it involves leakage from canals and overirrigation in the field often raises the underlying water table Rapid salination occurs when the land surface is within the capillary fringe of saline groundwater Soil salinity control involves watertable control and flushing with higher levels of applied water in combination with tile drainage or another form of subsurface drainage 235 236 Reclamation EditMain article Soil regeneration Soils which contain high levels of particular clays with high swelling properties such as smectites are often very fertile For example the smectite rich paddy soils of Thailand s Central Plains are among the most productive in the world However the overuse of mineral nitrogen fertilizers and pesticides in irrigated intensive rice production has endangered these soils forcing farmers to implement integrated practices based on Cost Reduction Operating Principles CROP 237 Many farmers in tropical areas however struggle to retain organic matter and clay in the soils they work In recent years for example productivity has declined and soil erosion has increased in the low clay soils of northern Thailand following the abandonment of shifting cultivation for a more permanent land use 238 Farmers initially responded by adding organic matter and clay from termite mound material but this was unsustainable in the long term because of rarefaction of termite mounds Scientists experimented with adding bentonite one of the smectite family of clays to the soil In field trials conducted by scientists from the International Water Management Institute in cooperation with Khon Kaen University and local farmers this had the effect of helping retain water and nutrients Supplementing the farmer s usual practice with a single application of 200 kg bentonite per rai 6 26 rai 1 hectare resulted in an average yield increase of 73 239 Other studies showed that applying bentonite to degraded sandy soils reduced the risk of crop failure during drought years 240 In 2008 three years after the initial trials IWMI scientists conducted a survey among 250 farmers in northeast Thailand half of whom had applied bentonite to their fields The average improvement for those using the clay addition was 18 higher than for non clay users Using the clay had enabled some farmers to switch to growing vegetables which need more fertile soil This helped to increase their income The researchers estimated that 200 farmers in northeast Thailand and 400 in Cambodia had adopted the use of clays and that a further 20 000 farmers were introduced to the new technique 241 If the soil is too high in clay or salts e g saline sodic soil adding gypsum washed river sand and organic matter e g municipal solid waste will balance the composition 242 Adding organic matter like ramial chipped wood or compost to soil which is depleted in nutrients and too high in sand will boost its quality and improve production 243 244 Special mention must be made of the use of charcoal and more generally biochar to improve nutrient poor tropical soils a process based on the higher fertility of anthropogenic pre Columbian Amazonian Dark Earths also called Terra Preta de Indio due to interesting physical and chemical properties of soil black carbon as a source of stable humus 245 However the uncontrolled application of charred waste products of all kinds may endanger soil life and human health 246 History of studies and research EditThe history of the study of soil is intimately tied to humans urgent need to provide food for themselves and forage for their animals Throughout history civilizations have prospered or declined as a function of the availability and productivity of their soils 247 Studies of soil fertility Edit Main article Soil fertility This section may contain an excessive amount of intricate detail that may interest only a particular audience Specifically details could be moved into main article Please help by spinning off or relocating any relevant information and removing excessive detail that may be against Wikipedia s inclusion policy April 2021 Learn how and when to remove this template message The Greek historian Xenophon 450 355 BCE is credited with being the first to expound upon the merits of green manuring crops But then whatever weeds are upon the ground being turned into earth enrich the soil as much as dung 248 Columella s Of husbandry circa 60 CE advocated the use of lime and that clover and alfalfa green manure should be turned under 249 and was used by 15 generations 450 years under the Roman Empire until its collapse 248 250 From the fall of Rome to the French Revolution knowledge of soil and agriculture was passed on from parent to child and as a result crop yields were low During the European Middle Ages Yahya Ibn al Awwam s handbook 251 with its emphasis on irrigation guided the people of North Africa Spain and the Middle East a translation of this work was finally carried to the southwest of the United States when under Spanish influence 252 Olivier de Serres considered as the father of French agronomy was the first to suggest the abandonment of fallowing and its replacement by hay meadows within crop rotations and he highlighted the importance of soil the French terroir in the management of vineyards His famous book Le Theatre d Agriculture et mesnage des champs 253 contributed to the rise of modern sustainable agriculture and to the collapse of old agricultural practices such as soil amendment for crops by the lifting of forest litter and assarting which ruined the soils of western Europe during the Middle Ages and even later on according to regions 254 Experiments into what made plants grow first led to the idea that the ash left behind when plant matter was burned was the essential element but overlooked the role of nitrogen which is not left on the ground after combustion a belief which prevailed until the 19th century 255 In about 1635 the Flemish chemist Jan Baptist van Helmont thought he had proved water to be the essential element from his famous five years experiment with a willow tree grown with only the addition of rainwater His conclusion came from the fact that the increase in the plant s weight had apparently been produced only by the addition of water with no reduction in the soil s weight 256 257 258 John Woodward d 1728 experimented with various types of water ranging from clean to muddy and found muddy water the best and so he concluded that earthy matter was the essential element Others concluded it was humus in the soil that passed some essence to the growing plant Still others held that the vital growth principal was something passed from dead plants or animals to the new plants At the start of the 18th century Jethro Tull demonstrated that it was beneficial to cultivate stir the soil but his opinion that the stirring made the fine parts of soil available for plant absorption was erroneous 257 259 As chemistry developed it was applied to the investigation of soil fertility The French chemist Antoine Lavoisier showed in about 1778 that plants and animals must combust oxygen internally to live and was able to deduce that most of the 165 pound weight of van Helmont s willow tree derived from air 260 It was the French agriculturalist Jean Baptiste Boussingault who by means of experimentation obtained evidence showing that the main sources of carbon hydrogen and oxygen for plants were air and water while nitrogen was taken from soil 261 Justus von Liebig in his book Organic chemistry in its applications to agriculture and physiology published 1840 asserted that the chemicals in plants must have come from the soil and air and that to maintain soil fertility the used minerals must be replaced 262 Liebig nevertheless believed the nitrogen was supplied from the air The enrichment of soil with guano by the Incas was rediscovered in 1802 by Alexander von Humboldt This led to its mining and that of Chilean nitrate and to its application to soil in the United States and Europe after 1840 263 The work of Liebig was a revolution for agriculture and so other investigators started experimentation based on it In England John Bennet Lawes and Joseph Henry Gilbert worked in the Rothamsted Experimental Station founded by the former and re discovered that plants took nitrogen from the soil and that salts needed to be in an available state to be absorbed by plants Their investigations also produced the superphosphate consisting in the acid treatment of phosphate rock 264 This led to the invention and use of salts of potassium K and nitrogen N as fertilizers Ammonia generated by the production of coke was recovered and used as fertiliser 265 Finally the chemical basis of nutrients delivered to the soil in manure was understood and in the mid 19th century chemical fertilisers were applied However the dynamic interaction of soil and its life forms still awaited discovery In 1856 J Thomas Way discovered that ammonia contained in fertilisers was transformed into nitrates 266 and twenty years later Robert Warington proved that this transformation was done by living organisms 267 In 1890 Sergei Winogradsky announced he had found the bacteria responsible for this transformation 268 It was known that certain legumes could take up nitrogen from the air and fix it to the soil but it took the development of bacteriology towards the end of the 19th century to lead to an understanding of the role played in nitrogen fixation by bacteria The symbiosis of bacteria and leguminous roots and the fixation of nitrogen by the bacteria were simultaneously discovered by the German agronomist Hermann Hellriegel and the Dutch microbiologist Martinus Beijerinck 264 Crop rotation mechanisation chemical and natural fertilisers led to a doubling of wheat yields in western Europe between 1800 and 1900 269 Studies of soil formation Edit See also Pedogenesis The scientists who studied the soil in connection with agricultural practices had considered it mainly as a static substrate However soil is the result of evolution from more ancient geological materials under the action of biotic and abiotic processes After studies of the improvement of the soil commenced other researchers began to study soil genesis and as a result also soil types and classifications In 1860 in Mississippi Eugene W Hilgard 1833 1916 studied the relationship between rock material climate vegetation and the type of soils that were developed He realised that the soils were dynamic and considered the classification of soil types 270 Unfortunately his work was not continued At about the same time Friedrich Albert Fallou was describing soil profiles and relating soil characteristics to their formation as part of his professional work evaluating forest and farm land for the principality of Saxony His 1857 book Anfangsgrunde der Bodenkunde First principles of soil science established modern soil science 271 Contemporary with Fallou s work and driven by the same need to accurately assess land for equitable taxation Vasily Dokuchaev led a team of soil scientists in Russia who conducted an extensive survey of soils observing that similar basic rocks climate and vegetation types lead to similar soil layering and types and established the concepts for soil classifications Due to language barriers the work of this team was not communicated to western Europe until 1914 through a publication in German by Konstantin Glinka a member of the Russian team 272 Curtis F Marbut influenced by the work of the Russian team translated Glinka s publication into English 273 and as he was placed in charge of the U S National Cooperative Soil Survey applied it to a national soil classification system 257 See also EditWikimedia Commons has media related to Soils Wikiquote has quotations related to SoilAcid sulfate soil Agrophysics Crust Agricultural science Factors affecting permeability of soils Index of soil related articles Mycorrhizal fungi and soil carbon storage Shrink swell capacity Soil biodiversity Soil liquefaction Soil moisture velocity equation Soil zoology Tillage erosion World Soil Museum Red soilReferences Edit Chesworth Ward ed 2008 Encyclopedia of soil science PDF Dordrecht The Netherlands Springer ISBN 978 1 4020 3994 2 Archived from the original PDF on 5 September 2018 Voroney R Paul Heck Richard J 2007 The soil habitat PDF In Paul Eldor A ed Soil microbiology ecology and biochemistry 3rd ed Amsterdam the Netherlands Elsevier pp 25 49 doi 10 1016 B978 0 08 047514 1 50006 8 ISBN 978 0 12 546807 7 Archived from the original PDF on 10 July 2018 Taylor Sterling A Ashcroft Gaylen L 1972 Physical edaphology the physics of irrigated and nonirrigated soils San Francisco California W H Freeman ISBN 978 0 7167 0818 6 McCarthy David F 2006 Essentials of soil mechanics and foundations basic geotechnics PDF 7th ed Upper Saddle River New Jersey Prentice Hall ISBN 978 0 13 114560 3 Retrieved 17 January 2021 Gilluly James Waters Aaron Clement Woodford Alfred Oswald 1975 Principles of geology 4th ed San Francisco California W H Freeman ISBN 978 0 7167 0269 6 Ponge Jean Francois 2015 The soil as an ecosystem Biology and Fertility of Soils 51 6 645 48 doi 10 1007 s00374 015 1016 1 S2CID 18251180 Retrieved 24 January 2021 Yu Charley Kamboj Sunita Wang Cheng Cheng Jing Jy 2015 Data collection handbook to support modeling impacts of radioactive material in soil and building structures PDF Argonne National Laboratory pp 13 21 Archived PDF from the original on 4 August 2018 Retrieved 24 January 2021 a b Buol Stanley W Southard Randal J Graham Robert C McDaniel Paul A 2011 Soil genesis and classification 7th ed Ames Iowa Wiley Blackwell ISBN 978 0 470 96060 8 Retallack Gregory J Krinsley David H Fischer Robert Razink Joshua J Langworthy Kurt A 2016 Archean coastal plain paleosols and life on land PDF Gondwana Research 40 1 20 Bibcode 2016GondR 40 1R doi 10 1016 j gr 2016 08 003 Archived PDF from the original on 13 November 2018 Retrieved 24 January 2021 Glossary of terms in soil science Agriculture and Agri Food Canada 13 December 2013 Archived from the original on 27 October 2018 Retrieved 24 January 2021 Amundson Ronald Soil preservation and the future of pedology PDF Faculty of Natural Resources Songkhla Thailand Prince of Songkla University Archived PDF from the original on 12 June 2018 Retrieved 24 January 2021 Kuppers Michael Vincent Jean Baptiste Impacts and formation of regolith Max Planck Institute for Solar System Research Archived from the original on 4 August 2018 Retrieved 24 January 2021 Amelung Wulf Bossio Deborah De Vries Wim Kogel Knabner Ingrid Lehmann Johannes Amundson Ronald Bol Roland Collins Chris Lal Rattan Leifeld Jens Minasny Buniman Pan Gen Xing Paustian Keith Rumpel Cornelia Sanderman Jonathan Van Groeningen Jan Willem Mooney Sian Van Wesemael Bas Wander Michelle Chabbi Abad 27 October 2020 Towards a global scale soil climate mitigation strategy Nature Communications 11 1 5427 Bibcode 2020NatCo 11 5427A doi 10 1038 s41467 020 18887 7 ISSN 2041 1723 PMC 7591914 PMID 33110065 Pouyat Richard Groffman Peter Yesilonis Ian Hernandez Luis 2002 Soil carbon pools and fluxes in urban ecosystems Environmental Pollution 116 Supplement 1 S107 S118 doi 10 1016 S0269 7491 01 00263 9 PMID 11833898 Retrieved 7 February 2021 Our analysis of pedon data from several disturbed soil profiles suggests that physical disturbances and anthropogenic inputs of various materials direct effects can greatly alter the amount of C stored in these human made soils Davidson Eric A Janssens Ivan A 2006 Temperature sensitivity of soil carbon decomposition and feedbacks to climate change PDF Nature 440 9 March 2006 165 73 Bibcode 2006Natur 440 165D doi 10 1038 nature04514 PMID 16525463 S2CID 4404915 Retrieved 7 February 2021 Powlson David 2005 Will soil amplify climate change PDF Nature 433 20 January 2005 204 05 Bibcode 2005Natur 433 204P doi 10 1038 433204a PMID 15662396 S2CID 35007042 Retrieved 7 February 2021 Bradford Mark A Wieder William R Bonan Gordon B Fierer Noah Raymond Peter A Crowther Thomas W 2016 Managing uncertainty in soil carbon feedbacks to climate change PDF Nature Climate Change 6 27 July 2016 751 58 Bibcode 2016NatCC 6 751B doi 10 1038 nclimate3071 hdl 20 500 11755 c1792dbf ce96 4dc7 8851 1ca50a35e5e0 Retrieved 7 February 2021 Dominati Estelle Patterson Murray Mackay Alec 2010 A framework for classifying and quantifying the natural capital and ecosystem services of soils Ecological Economics 69 9 1858 68 doi 10 1016 j ecolecon 2010 05 002 Archived PDF from the original on 8 August 2017 Retrieved 14 February 2021 Dykhuizen Daniel E 1998 Santa Rosalia revisited why are there so many species of bacteria Antonie van Leeuwenhoek 73 1 25 33 doi 10 1023 A 1000665216662 PMID 9602276 S2CID 17779069 Retrieved 14 February 2021 Torsvik Vigdis Ovreas Lise 2002 Microbial diversity and function in soil from genes to ecosystems Current Opinion in Microbiology 5 3 240 45 doi 10 1016 S1369 5274 02 00324 7 PMID 12057676 Retrieved 14 February 2021 Raynaud Xavier Nunan Naoise 2014 Spatial ecology of bacteria at the microscale in soil PLOS ONE 9 1 e87217 Bibcode 2014PLoSO 987217R doi 10 1371 journal pone 0087217 PMC 3905020 PMID 24489873 Whitman William B Coleman David C Wiebe William J 1998 Prokaryotes the unseen majority Proceedings of the National Academy of Sciences of the USA 95 12 6578 83 Bibcode 1998PNAS 95 6578W doi 10 1073 pnas 95 12 6578 PMC 33863 PMID 9618454 Schlesinger William H Andrews Jeffrey A 2000 Soil respiration and the global carbon cycle Biogeochemistry 48 1 7 20 doi 10 1023 A 1006247623877 S2CID 94252768 Retrieved 14 February 2021 Denmead Owen Thomas Shaw Robert Harold 1962 Availability of soil water to plants as affected by soil moisture content and meteorological conditions Agronomy Journal 54 5 385 90 doi 10 2134 agronj1962 00021962005400050005x Retrieved 14 February 2021 House Christopher H Bergmann Ben A Stomp Anne Marie Frederick Douglas J 1999 Combining constructed wetlands and aquatic and soil filters for reclamation and reuse of water Ecological Engineering 12 1 2 27 38 doi 10 1016 S0925 8574 98 00052 4 Retrieved 14 February 2021 Van Bruggen Ariena H C Semenov Alexander M 2000 In search of biological indicators for soil health and disease suppression Applied Soil Ecology 15 1 13 24 doi 10 1016 S0929 1393 00 00068 8 Retrieved 14 February 2021 A citizen s guide to monitored natural attenuation PDF Retrieved 14 February 2021 Linn Daniel Myron Doran John W 1984 Effect of water filled pore space on carbon dioxide and nitrous oxide production in tilled and nontilled soils Soil Science Society of America Journal 48 6 1267 72 Bibcode 1984SSASJ 48 1267L doi 10 2136 sssaj1984 03615995004800060013x Retrieved 14 February 2021 Miller Raymond W Donahue Roy Luther 1990 Soils an introduction to soils and plant growth Upper Saddle River New Jersey Prentice Hall ISBN 978 0 13 820226 2 Bot Alexandra Benites Jose 2005 The importance of soil organic matter key to drought resistant soil and sustained food and production PDF Rome Food and Agriculture Organization of the United Nations ISBN 978 92 5 105366 9 Retrieved 14 February 2021 McClellan Tai Soil composition University of Hawai i at Manoa College of Tropical Agriculture and Human Resources Retrieved 21 February 2021 Arizona Master Gardener Manual Cooperative Extension College of Agriculture University of Arizona 9 November 2017 Archived from the original on 29 May 2016 Retrieved 17 December 2017 a b Vannier Guy 1987 The porosphere as an ecological medium emphasized in Professor Ghilarov s work on soil animal adaptations PDF Biology and Fertility of Soils 3 1 39 44 doi 10 1007 BF00260577 S2CID 297400 Retrieved 21 February 2021 Torbert H Allen Wood Wes 1992 Effect of soil compaction and water filled pore space on soil microbial activity and N losses Communications in Soil Science and Plant Analysis 23 11 1321 31 doi 10 1080 00103629209368668 Retrieved 21 February 2021 Simonson 1957 p 17 Zanella Augusto Katzensteiner Klaus Ponge Jean Francois Jabiol Bernard Sartori Giacomo Kolb Eckart Le Bayon Renee Claire Aubert Michael Ascher Jenull Judith Englisch Michael Hager Herbert June 2019 TerrHum an iOS App for classifying terrestrial humipedons and some considerations about soil classification Soil Science Society of America Journal 83 S1 S42 S48 doi 10 2136 sssaj2018 07 0279 S2CID 197555747 Retrieved 28 February 2021 Bronick Carol J Lal Ratan January 2005 Soil structure and management a review PDF Geoderma 124 1 2 3 22 Bibcode 2005Geode 124 3B doi 10 1016 j geoderma 2004 03 005 Retrieved 21 February 2021 Soil and water Food and Agriculture Organization of the United Nations Retrieved 21 February 2021 Valentin Christian d Herbes Jean Marc Poesen Jean 1999 Soil and water components of banded vegetation patterns Catena 37 1 1 24 doi 10 1016 S0341 8162 99 00053 3 Retrieved 21 February 2021 Brady Nyle C Weil Ray R 2007 The colloidal fraction seat of soil chemical and physical activity In Brady Nyle C Weil Ray R eds The nature and properties of soils 14th ed London United Kingdom Pearson pp 310 57 ISBN 978 0132279383 Retrieved 21 February 2021 Soil colloids properties nature types and significance PDF Tamil Nadu Agricultural University Retrieved 7 March 2021 a b Cation exchange capacity in soils simplified Retrieved 7 March 2021 Miller Jarrod O Soil pH affects nutrient availability PDF University of Maryland Retrieved 7 March 2021 Goulding Keith W T Bailey Neal J Bradbury Nicola J Hargreaves Patrick Howe M T Murphy Daniel V Poulton Paul R Willison Toby W 1998 Nitrogen deposition and its contribution to nitrogen cycling and associated soil processes New Phytologist 139 1 49 58 doi 10 1046 j 1469 8137 1998 00182 x Kononova M M 2013 Soil organic matter its nature its role in soil formation and in soil fertility 2nd ed Amsterdam The Netherlands Elsevier ISBN 978 1 4831 8568 2 Burns Richards G DeForest Jared L Marxsen Jurgen Sinsabaugh Robert L Stromberger Mary E Wallenstein Matthew D Weintraub Michael N Zoppini Annamaria 2013 Soil enzymes in a changing environment current knowledge and future directions Soil Biology and Biochemistry 58 216 34 doi 10 1016 j soilbio 2012 11 009 Sengupta Aditi Kushwaha Priyanka Jim Antonia Troch Peter A Maier Raina 2020 New soil old plants and ubiquitous microbes evaluating the potential of incipient basaltic soil to support native plant growth and influence belowground soil microbial community composition Sustainability 12 10 4209 doi 10 3390 su12104209 Bishop Janice L Murchie Scott L Pieters Carle L Zent Aaron P 2002 A model for formation of dust soil and rock coatings on Mars physical and chemical processes on the Martian surface Journal of Geophysical Research 107 E11 7 1 7 17 Bibcode 2002JGRE 107 5097B doi 10 1029 2001JE001581 Navarro Gonzalez Rafael Rainey Fred A Molina Paola Bagaley Danielle R Hollen Becky J de la Rosa Jose Small Alanna M Quinn Richard C Grunthaner Frank J Caceres Luis Gomez Silva Benito McKay Christopher P 2003 Mars like soils in the Atacama desert Chile and the dry limit of microbial life Science 302 5647 1018 21 Bibcode 2003Sci 302 1018N doi 10 1126 science 1089143 PMID 14605363 S2CID 18220447 Retrieved 14 March 2021 Guo Yong Fujimura Reiko Sato Yoshinori Suda Wataru Kim Seok won Oshima Kenshiro Hattori Masahira Kamijo Takashi Narisawa Kazuhiko Ohta Hiroyuki 2014 Characterization of early microbial communities on volcanic deposits along a vegetation gradient on the island of Miyake Japan Microbes and Environments 29 1 38 49 doi 10 1264 jsme2 ME13142 PMC 4041228 PMID 24463576 Goldich Samuel S 1938 A study in tock weathering The Journal of Geology 46 1 17 58 Bibcode 1938JG 46 17G doi 10 1086 624619 ISSN 0022 1376 S2CID 128498195 Retrieved 29 September 2021 Van Scholl Laura Smits Mark M Hoffland Ellis 2006 Ectomycorrhizal weathering of the soil minerals muscovite and hornblende New Phytologist 171 4 805 14 doi 10 1111 j 1469 8137 2006 01790 x PMID 16918551 Stretch Rachelle C Viles Heather A 2002 The nature and rate of weathering by lichens on lava flows on Lanzarote Geomorphology 47 1 87 94 Bibcode 2002Geomo 47 87S doi 10 1016 S0169 555X 02 00143 5 Retrieved 21 March 2021 Dojani Stephanie Lakatos Michael Rascher Uwe Waneck Wolfgang Luettge Ulrich Budel Burkhard 2007 Nitrogen input by cyanobacterial biofilms of an inselberg into a tropical rainforest in French Guiana Flora 202 7 521 29 doi 10 1016 j flora 2006 12 001 Retrieved 21 March 2021 Kabala Cesary Kubicz Justyna 2012 Initial soil development and carbon accumulation on moraines of the rapidly retreating Werenskiold Glacier SW Spitsbergen Svalbard archipelago Geoderma 175 176 9 20 Bibcode 2012Geode 175 9K doi 10 1016 j geoderma 2012 01 025 Retrieved 26 May 2019 Jenny Hans 1941 Factors of soil formation a system of qunatitative pedology PDF New York McGraw Hill Archived PDF from the original on 8 August 2017 Retrieved 21 March 2021 Ritter Michael E The physical environment an introduction to physical geography PDF Retrieved 21 March 2021 Gardner Catriona M K Laryea Kofi Buna Unger Paul W 1999 Soil physical constraints to plant growth and crop production PDF 1st ed Rome Food and Agriculture Organization of the United Nations Archived from the original PDF on 8 August 2017 Retrieved 24 December 2017 Six Johan Paustian Keith Elliott Edward T Combrink Clay 2000 Soil structure and organic matter I Distribution of aggregate size classes and aggregate associated carbon Soil Science Society of America Journal 64 2 681 89 Bibcode 2000SSASJ 64 681S doi 10 2136 sssaj2000 642681x Retrieved 28 March 2021 Hakansson Inge Lipiec Jerzy 2000 A review of the usefulness of relative bulk density values in studies of soil structure and compaction PDF Soil and Tillage Research 53 2 71 85 doi 10 1016 S0167 1987 99 00095 1 S2CID 30045538 Retrieved 28 March 2021 Schwerdtfeger W J 1965 Soil resistivity as related to underground corrosion and cathodic protection Journal of Research of the National Bureau of Standards 69C 1 71 77 doi 10 6028 jres 069c 012 Tamboli Prabhakar Mahadeo 1961 The influence of bulk density and aggregate size on soil moisture retention Ames Iowa Iowa State University Retrieved 28 March 2021 Qi Jingen Marshall John D Mattson Kim G 1994 High soil carbon dioxide concentrations inhibit root respiration of Douglas fir New Phytologist 128 3 435 42 doi 10 1111 j 1469 8137 1994 tb02989 x PMID 33874575 Karberg Noah J Pregitzer Kurt S King John S Friend Aaron L Wood James R 2005 Soil carbon dioxide partial pressure and dissolved inorganic carbonate chemistry under elevated carbon dioxide and ozone PDF Oecologia 142 2 296 306 Bibcode 2005Oecol 142 296K doi 10 1007 s00442 004 1665 5 PMID 15378342 S2CID 6161016 Retrieved 25 April 2021 Chang H T Loomis W E 1945 Effect of carbon dioxide on absorption of water and nutrients by roots Plant Physiology 20 2 221 32 doi 10 1104 pp 20 2 221 PMC 437214 PMID 16653979 McDowell Nate J Marshall John D Qi Jingen Mattson Kim 1999 Direct inhibition of maintenance respiration in western hemlock roots exposed to ambient soil carbon dioxide concentrations Tree Physiology 19 9 599 605 doi 10 1093 treephys 19 9 599 PMID 12651534 Xu Xia Nieber John L Gupta Satish C 1992 Compaction effect on the gas diffusion coefficient in soils Soil Science Society of America Journal 56 6 1743 50 Bibcode 1992SSASJ 56 1743X doi 10 2136 sssaj1992 03615995005600060014x Retrieved 25 April 2021 a b Smith Keith A Ball Tom Conen Franz Dobbie Karen E Massheder Jonathan Rey Ana 2003 Exchange of greenhouse gases between soil and atmosphere interactions of soil physical factors and biological processes European Journal of Soil Science 54 4 779 91 doi 10 1046 j 1351 0754 2003 0567 x S2CID 18442559 Retrieved 25 April 2021 Russell 1957 pp 35 36 Ruser Reiner Flessa Heiner Russow Rolf Schmidt G Buegger Franz Munch J C 2006 Emission of N2O N2 and CO2 from soil fertilized with nitrate effect of compaction soil moisture and rewetting Soil Biology and Biochemistry 38 2 263 74 doi 10 1016 j soilbio 2005 05 005 Retrieved 25 April 2021 Hartmann Adrian A Buchmann Nina Niklaus Pascal A 2011 A study of soil methane sink regulation in two grasslands exposed to drought and N fertilization Plant and Soil 342 1 2 265 75 doi 10 1007 s11104 010 0690 x hdl 20 500 11850 34759 S2CID 25691034 Moore Tim R Dalva Moshe 1993 The influence of temperature and water table position on carbon dioxide and methane emissions from laboratory columns of peatland soils Journal of Soil Science 44 4 651 64 doi 10 1111 j 1365 2389 1993 tb02330 x Retrieved 25 April 2021 Hiltpold Ivan Toepfer Stefan Kuhlmann Ulrich Turlings Ted C J 2010 How maize root volatiles affect the efficacy of entomopathogenic nematodes in controlling the western corn rootworm Chemoecology 20 2 155 62 doi 10 1007 s00049 009 0034 6 S2CID 30214059 Retrieved 2 May 2021 Ryu Choong Min Farag Mohamed A Hu Chia Hui Reddy Munagala S Wei Han Xun Pare Paul W Kloepper Joseph W 2003 Bacterial volatiles promote growth in Arabidopsis PDF Proceedings of the National Academy of Sciences of the United States of America 100 8 4927 32 Bibcode 2003PNAS 100 4927R doi 10 1073 pnas 0730845100 PMC 153657 PMID 12684534 Retrieved 2 May 2021 Hung Richard Lee Samantha Bennett Joan W 2015 Fungal volatile organic compounds and their role in ecosystems Applied Microbiology and Biotechnology 99 8 3395 405 doi 10 1007 s00253 015 6494 4 PMID 25773975 S2CID 14509047 Retrieved 2 May 2021 Purrington Foster Forbes Kendall Paricia A Bater John E Stinner Benjamin R 1991 Alarm pheromone in a gregarious poduromorph collembolan Collembola Hypogastruridae Great Lakes Entomologist 24 2 75 78 Retrieved 2 May 2021 Badri Dayakar V Weir Tiffany L Van der Lelie Daniel Vivanco Jorge M 2009 Rhizosphere chemical dialogues plant microbe interactions PDF Current Opinion in Biotechnology 20 6 642 50 doi 10 1016 j copbio 2009 09 014 PMID 19875278 Salmon Sandrine Ponge Jean Francois 2001 Earthworm excreta attract soil springtails laboratory experiments on Heteromurus nitidus Collembola Entomobryidae Soil Biology and Biochemistry 33 14 1959 69 doi 10 1016 S0038 0717 01 00129 8 Retrieved 2 May 2021 Lambers Hans Mougel Christophe Jaillard Benoit Hinsinger Philipe 2009 Plant microbe soil interactions in the rhizosphere an evolutionary perspective Plant and Soil 321 1 2 83 115 doi 10 1007 s11104 009 0042 x S2CID 6840457 Retrieved 2 May 2021 Penuelas Josep Asensio Dolores Tholl Dorothea Wenke Katrin Rosenkranz Maaria Piechulla Birgit Schnitzler Jorg Petter 2014 Biogenic volatile emissions from the soil Plant Cell and Environment 37 8 1866 91 doi 10 1111 pce 12340 PMID 24689847 Buzuleciu Samuel A Crane Derek P Parker Scott L 2016 Scent of disinterred soil as an olfactory cue used by raccoons to locate nests of diamond backed terrapins Malaclemys terrapin PDF Herpetological Conservation and Biology 11 3 539 51 Retrieved 2 May 2021 Saxton Keith E Rawls Walter J 2006 Soil water characteristic estimates by texture and organic matter for hydrologic solutions PDF Soil Science Society of America Journal 70 5 1569 78 Bibcode 2006SSASJ 70 1569S CiteSeerX 10 1 1 452 9733 doi 10 2136 sssaj2005 0117 S2CID 16826314 Archived PDF from the original on 2 September 2018 Retrieved 2 May 2021 College of Tropical Agriculture and Human Resources Soil mineralogy University of Hawaiʻi at Manoa Retrieved 2 May 2021 Sposito Garrison 1984 The surface chemistry of soils New York New York Oxford University Press Retrieved 2 May 2021 Wynot Christopher Theory of diffusion in colloidal suspensions Retrieved 2 May 2021 Donahue Miller amp Shickluna 1977 p 103 06 Sposito Garrison Skipper Neal T Sutton Rebecca Park Sung Ho Soper Alan K Greathouse Jeffery A 1999 Surface geochemistry of the clay minerals Proceedings of the National Academy of Sciences of the United States of America 96 7 3358 64 Bibcode 1999PNAS 96 3358S doi 10 1073 pnas 96 7 3358 PMC 34275 PMID 10097044 Bickmore Barry R Rosso Kevin M Nagy Kathryn L Cygan Randall T Tadanier Christopher J 2003 Ab initio determination of edge surface structures for dioctahedral 2 1 phyllosilicates implications for acid base reactivity PDF Clays and Clay Minerals 51 4 359 71 Bibcode 2003CCM 51 359B doi 10 1346 CCMN 2003 0510401 S2CID 97428106 Retrieved 9 May 2021 Rajamathi Michael Thomas Grace S Kamath P Vishnu 2001 The many ways of making anionic clays Journal of Chemical Sciences 113 5 6 671 80 doi 10 1007 BF02708799 S2CID 97507578 Moayedi Hossein Kazemian Sina 2012 Zeta potentials of suspended humus in multivalent cationic saline solution and its effect on electro osomosis behavior Journal of Dispersion Science and Technology 34 2 283 94 doi 10 1080 01932691 2011 646601 S2CID 94333872 Retrieved 9 May 2021 Pettit Robert E Organic matter humus humate humic acid fulvic acid and humin their importance in soil fertility and plant health PDF Retrieved 16 May 2021 Diamond Sidney Kinter Earl B 1965 Mechanisms of soil lime stabilization an interpretive review PDF Highway Research Record 92 83 102 Retrieved 16 May 2021 Woodruff Clarence M 1955 The energies of replacement of calcium by potassium in soils PDF Soil Science Society of America Journal 19 2 167 71 Bibcode 1955SSASJ 19 167W doi 10 2136 sssaj1955 03615995001900020014x Retrieved 16 May 2021 Fronaeus Sture 1953 On the application of the mass action law to cation exchange equilibria Acta Chemica Scandinavica 7 469 80 doi 10 3891 acta chem scand 07 0469 Bolland Mike D A Posner Alan M Quirk James P 1980 pH independent and pH dependent surface charges on kaolinite Clays and Clay Minerals 28 6 412 18 Bibcode 1980CCM 28 412B CiteSeerX 10 1 1 543 8017 doi 10 1346 CCMN 1980 0280602 S2CID 12462516 Retrieved 16 May 2021 Silber Avner Levkovitch Irit Graber Ellen R 2010 pH dependent mineral release and surface properties of cornstraw biochar agronomic implications Environmental Science and Technology 44 24 9318 23 Bibcode 2010EnST 44 9318S doi 10 1021 es101283d PMID 21090742 Retrieved 16 May 2021 Dakora Felix D Phillips Donald D 2002 Root exudates as mediators of mineral acquisition in low nutrient environments Plant and Soil 245 35 47 doi 10 1023 A 1020809400075 S2CID 3330737 Archived PDF from the original on 19 August 2019 Retrieved 16 May 2021 Brown John C 1978 Mechanism of iron uptake by plants Plant Cell and Environment 1 4 249 57 doi 10 1111 j 1365 3040 1978 tb02037 x Donahue Miller amp Shickluna 1977 p 114 Singh Jamuna Sharan Raghubanshi Akhilesh Singh Singh Raj S Srivastava S C 1989 Microbial biomass acts as a source of plant nutrient in dry tropical forest and savanna Nature 338 6215 499 500 Bibcode 1989Natur 338 499S doi 10 1038 338499a0 S2CID 4301023 Retrieved 23 May 2021 Szatanik Kloc Alicja Szerement Justyna Jozefaciuk Grzegorz 2017 The role of cell walls and pectins in cation exchange and surface area of plant roots Journal of Plant Physiology 215 85 90 doi 10 1016 j jplph 2017 05 017 PMID 28600926 Retrieved 23 May 2021 a b Donahue Miller amp Shickluna 1977 pp 115 16 a b Hinsinger Philippe 2001 Bioavailability of soil inorganic P in the rhizosphere as affected by root induced chemical changes a review Plant and Soil 237 2 173 95 doi 10 1023 A 1013351617532 Gu Baohua Schulz Robert K 1991 Anion retention in soil possible application to reduce migration of buried technetium and iodine a review doi 10 2172 5980032 Cite journal requires journal help Lawrinenko Michael Jing Dapeng Banik Chumki Laird David A 2017 Aluminum and iron biomass pretreatment impacts on biochar anion exchange capacity Carbon 118 422 30 doi 10 1016 j carbon 2017 03 056 Sollins Phillip Robertson G Philip Uehara Goro 1988 Nutrient mobility in variable and permanent charge soils PDF Biogeochemistry 6 3 181 99 doi 10 1007 BF02182995 S2CID 4505438 Sanders W M H 1964 Extraction of soil phosphate by anion exchange membrane New Zealand Journal of Agricultural Research 7 3 427 31 doi 10 1080 00288233 1964 10416423 Lawrinenko Mike Laird David A 2015 Anion exchange capacity of biochar Green Chemistry 17 9 4628 36 doi 10 1039 C5GC00828J Retrieved 30 May 2021 Robertson Bryan pH requirements of freshwater aquatic life PDF Retrieved 6 June 2021 Chang Raymond ed 2010 Chemistry Chemistry Chang 12Ed 12th ed New York New York McGraw Hill p 666 ISBN 9780078021510 Retrieved 6 June 2021 Singleton Peter L Edmeades Doug C Smart R E Wheeler David M 2001 The many ways of making anionic clays Journal of Chemical Sciences 113 5 6 671 80 doi 10 1007 BF02708799 S2CID 97507578 Lauchli Andre Grattan Steve R 2012 Soil pH extremes In Shabala Sergey ed Plant stress physiology 1st ed Wallingford United Kingdom CAB International pp 194 209 doi 10 1079 9781845939953 0194 ISBN 978 1845939953 Retrieved 13 June 2021 Donahue Miller amp Shickluna 1977 pp 116 17 Calmano Wolfgang Hong Jihua Forstner Ulrich 1993 Binding and mobilization of heavy metals in contaminated sediments affected by pH and redox potential Water Science and Technology 28 8 9 223 35 doi 10 2166 wst 1993 0622 Retrieved 13 June 2021 Ren Xiaoya Zeng Guangming Tang Lin Wang Jingjing Wan Jia Liu Yani Yu Jiangfang Yi Huan Ye Shujing Deng Rui 2018 Sorption transport and biodegradation an insight into bioavailability of persistent organic pollutants in soil PDF Science of the Total Environment 610 611 1154 63 Bibcode 2018ScTEn 610 1154R doi 10 1016 j scitotenv 2017 08 089 PMID 28847136 Retrieved 13 June 2021 Ponge Jean Francois 2003 Humus forms in terrestrial ecosystems a framework to biodiversity Soil Biology and Biochemistry 35 7 935 45 CiteSeerX 10 1 1 467 4937 doi 10 1016 S0038 0717 03 00149 4 Retrieved 13 June 2021 Fujii Kazumichi 2003 Soil acidification and adaptations of plants and microorganisms in Bornean tropical forests Ecological Research 29 3 371 81 doi 10 1007 s11284 014 1144 3 Kauppi Pekka Kamari Juha Posch Maximilian Kauppi Lea 1986 Acidification of forest soils model development and application for analyzing impacts of acidic deposition in Europe PDF Ecological Modelling 33 2 4 231 53 doi 10 1016 0304 3800 86 90042 6 Retrieved 13 June 2021 Andriesse Jacobus Pieter 1969 A study of the environment and characteristics of tropical podzols in Sarawak East Malaysia Geoderma 2 3 201 27 Bibcode 1969Geode 2 201A doi 10 1016 0016 7061 69 90038 X Retrieved 13 June 2021 Rengasamy Pichu 2006 World salinization with emphasis on Australia Journal of Experimental Botany 57 5 1017 23 doi 10 1093 jxb erj108 PMID 16510516 Arnon Daniel I Johnson Clarence M 1942 Influence of hydrogen ion concentration on the growth of higher plants under controlled conditions Plant Physiology 17 4 525 39 doi 10 1104 pp 17 4 525 PMC 438054 PMID 16653803 Chaney Rufus L Brown John C Tiffin Lee O 1972 Obligatory reduction of ferric chelates in iron uptake by soybeans Plant Physiology 50 2 208 13 doi 10 1104 pp 50 2 208 PMC 366111 PMID 16658143 Donahue Miller amp Shickluna 1977 pp 116 19 Ahmad Sagheer Ghafoor Abdul Qadir Manzoor Aziz M Abbas 2006 Amelioration of a calcareous saline sodic soil by gypsum application and different crop rotations International Journal of Agriculture and Biology 8 2 142 46 Retrieved 13 June 2021 McFee William W Kelly J Michael Beck Robert H 1977 Acid precipitation effects on soil pH and base saturation of exchange sites Water Air and Soil Pollution 7 3 401 08 Bibcode 1977WASP 7 401M doi 10 1007 BF00284134 Farina Martin Patrick W Sumner Malcolm E Plank C Owen Letzsch W Stephen 1980 Exchangeable aluminum and pH as indicators of lime requirement for corn Soil Science Society of America Journal 44 5 1036 41 Bibcode 1980SSASJ 44 1036F doi 10 2136 sssaj1980 03615995004400050033x Retrieved 20 June 2021 Donahue Miller amp Shickluna 1977 pp 119 20 Sposito Garrison Skipper Neal T Sutton Rebecca Park Sun Ho Soper Alan K Greathouse Jeffery A 1999 Surface geochemistry of the clay minerals Proceedings of the National Academy of Sciences of the United States of America 96 7 3358 64 Bibcode 1999PNAS 96 3358S doi 10 1073 pnas 96 7 3358 PMC 34275 PMID 10097044 Sparks Donald L Acidic and basic soils buffering PDF Davis California University of California Davis Department of Land Air and Water Resources Retrieved 20 June 2021 Ulrich Bernhard 1983 Soil acidity and its relations to acid deposition PDF In Ulrich Bernhard Pankrath Jurgen eds Effects of accumulation of air pollutants in forest ecosystems 1st ed Dordrecht The Netherlands D Reidel Publishing Company pp 127 46 doi 10 1007 978 94 009 6983 4 10 ISBN 978 94 009 6985 8 Retrieved 21 June 2021 Donahue Miller amp Shickluna 1977 pp 120 21 Donahue Miller amp Shickluna 1977 p 125 Dean 1957 p 80 Russel 1957 pp 123 25 a b Brady Nyle C Weil Ray R 2008 The nature and properties of soils 15th ed Upper Saddle River New Jersey Pearson ISBN 978 0 13 325448 8 Retrieved 27 June 2021 Van der Ploeg Rienk R Bohm Wolfgang Kirkham Mary Beth 1999 On the origin of the theory of mineral nutrition of plants and the Law of the Minimum Soil Science Society of America Journal 63 5 1055 62 Bibcode 1999SSASJ 63 1055V CiteSeerX 10 1 1 475 7392 doi 10 2136 sssaj1999 6351055x Knecht Magnus F Goransson Anders 2004 Terrestrial plants require nutrients in similar proportions Tree Physiology 24 4 447 60 doi 10 1093 treephys 24 4 447 PMID 14757584 Dean 1957 pp 80 81 a b Roy R N Finck Arnold Blair Graeme J Tandon Hari Lal Singh 2006 Soil fertility and crop production PDF Plant nutrition for food security a guide for integrated nutrient management Rome Italy Food and Agriculture Organization of the United Nations pp 43 90 ISBN 978 92 5 105490 1 Retrieved 27 June 2021 Parfitt Roger L Giltrap Donna J Whitton Joe S 1995 Contribution of organic matter and clay minerals to the cation exchange capacity of soil Communications in Soil Science and Plant Analysis 26 9 10 1343 55 doi 10 1080 00103629509369376 Retrieved 27 June 2021 Hajnos Mieczyslaw Jozefaciuk Grzegorz Sokolowska Zofia Greiffenhagen Andreas Wessolek Gerd 2003 Water storage surface and structural properties of sandy forest humus horizons Journal of Plant Nutrition and Soil Science 166 5 625 34 doi 10 1002 jpln 200321161 Retrieved 27 June 2021 Donahue Miller amp Shickluna 1977 pp 123 31 Pimentel David Harvey Celia Resosudarmo Pradnja Sinclair K Kurz D McNair M Crist S Shpritz L Fitton L Saffouri R Blair R 1995 Environmental and economic costs of soil erosion and conservation benefits Science 267 5201 1117 23 Bibcode 1995Sci 267 1117P doi 10 1126 science 267 5201 1117 PMID 17789193 S2CID 11936877 Archived PDF from the original on 13 December 2016 Retrieved 4 July 2021 Schnurer Johan Clarholm Marianne Rosswall Thomas 1985 Microbial biomass and activity in an agricultural soil with different organic matter contents Soil Biology and Biochemistry 17 5 611 18 doi 10 1016 0038 0717 85 90036 7 Retrieved 4 July 2021 Sparling Graham P 1992 Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter Australian Journal of Soil Research 30 2 195 207 doi 10 1071 SR9920195 Retrieved 4 July 2021 Varadachari Chandrika Ghosh Kunal 1984 On humus formation Plant and Soil 77 2 305 13 doi 10 1007 BF02182933 S2CID 45102095 Prescott Cindy E 2010 Litter decomposition what controls it and how can we alter it to sequester more carbon in forest soils Biogeochemistry 101 1 133 49 doi 10 1007 s10533 010 9439 0 S2CID 93834812 Lehmann Johannes Kleber Markus 2015 The contentious nature of soil organic matter PDF Nature 528 7580 60 68 Bibcode 2015Natur 528 60L doi 10 1038 nature16069 PMID 26595271 S2CID 205246638 Retrieved 4 July 2021 a b Piccolo Alessandro 2002 The supramolecular structure of humic substances a novel understanding of humus chemistry and implications in soil science Advances in Agronomy 75 57 134 doi 10 1016 S0065 2113 02 75003 7 ISBN 9780120007936 Retrieved 4 July 2021 Scheu Stefan 2002 The soil food web structure and perspectives European Journal of Soil Biology 38 1 11 20 doi 10 1016 S1164 5563 01 01117 7 Retrieved 4 July 2021 a b Foth Henry D 1984 Fundamentals of soil science PDF 8th ed New York New York Wiley p 139 ISBN 978 0471522799 Retrieved 4 July 2021 a b c Ponge Jean Francois 2003 Humus forms in terrestrial ecosystems a framework to biodiversity Soil Biology and Biochemistry 35 7 935 45 CiteSeerX 10 1 1 467 4937 doi 10 1016 S0038 0717 03 00149 4 Archived from the original on 29 January 2016 Pettit Robert E Organic matter humus humate humic acid fulvic acid and humin their importance in soil fertility and plant health PDF Retrieved 11 July 2021 Ji Rong Kappler Andreas Brune Andreas 2000 Transformation and mineralization of synthetic 14C labeled humic model compounds by soil feeding termites Soil Biology and Biochemistry 32 8 9 1281 91 CiteSeerX 10 1 1 476 9400 doi 10 1016 S0038 0717 00 00046 8 Retrieved 11 July 2021 Drever James I Vance George F 1994 Role of soil organic acids in mineral weathering processes PDF In Pittman Edward D Lewan Michael D eds Organic acids in geological processes Berlin Germany Springer pp 138 61 doi 10 1007 978 3 642 78356 2 6 ISBN 978 3 642 78356 2 Retrieved 11 July 2021 a b Piccolo Alessandro 1996 Humus and soil conservation In Piccolo Alessandro ed Humic substances in terrestrial ecosystems Amsterdam The Netherlands Elsevier pp 225 64 doi 10 1016 B978 044481516 3 50006 2 ISBN 978 0 444 81516 3 Retrieved 11 July 2021 Varadachari Chandrika Ghosh Kunal 1984 On humus formation Plant and Soil 77 2 305 13 doi 10 1007 BF02182933 S2CID 45102095 Retrieved 11 July 2021 Mendonca Eduardo S Rowell David L 1996 Mineral and organic fractions of two oxisols and their influence on effective cation exchange capacity Soil Science Society of America Journal 60 6 1888 92 Bibcode 1996SSASJ 60 1888M doi 10 2136 sssaj1996 03615995006000060038x Retrieved 11 July 2021 Heck Tobias Faccio Greta Richter Michael Thony Meyer Linda 2013 Enzyme catalyzed protein crosslinking Applied Microbiology and Biotechnology 97 2 461 75 doi 10 1007 s00253 012 4569 z PMC 3546294 PMID 23179622 Retrieved 11 July 2021 Lynch D L Lynch C C 1958 Resistance of protein lignin complexes lignins and humic acids to microbial attack PDF Nature 181 4621 1478 79 Bibcode 1958Natur 181 1478L doi 10 1038 1811478a0 PMID 13552710 S2CID 4193782 Retrieved 11 July 2021 Dawson Lorna A Hillier Stephen 2010 Measurement of soil characteristics for forensic applications PDF Surface and Interface Analysis 42 5 363 77 doi 10 1002 sia 3315 Retrieved 18 July 2021 Manjaiah K M Kumar Sarvendra Sachdev M S Sachdev P Datta S C 2010 Study of clay organic complexes Current Science 98 7 915 21 Retrieved 18 July 2021 Theng Benny K G 1982 Clay polymer interactions summary and perspectives Clays and Clay Minerals 30 1 1 10 Bibcode 1982CCM 30 1T CiteSeerX 10 1 1 608 2942 doi 10 1346 CCMN 1982 0300101 S2CID 98176725 Retrieved 18 July 2021 Tietjen Todd Wetzel Robert G 2003 Extracellular enzyme clay mineral complexes enzyme adsorption alteration of enzyme activity and protection from photodegradation PDF Aquatic Ecology 37 4 331 39 doi 10 1023 B AECO 0000007044 52801 6b S2CID 6930871 Retrieved 18 July 2021 Tahir Shermeen Marschner Petra 2017 Clay addition to sandy soil influence of clay type and size on nutrient availability in sandy soils amended with residues differing in C N ratio Pedosphere 27 2 293 305 doi 10 1016 S1002 0160 17 60317 5 Retrieved 18 July 2021 Melero Sebastiana Madejon Engracia Ruiz Juan Carlos Herencia Juan Francisco 2007 Chemical and biochemical properties of a clay soil under dryland agriculture system as affected by organic fertilization European Journal of Agronomy 26 3 327 34 doi 10 1016 j eja 2006 11 004 Retrieved 18 July 2021 Joanisse Gilles D Bradley Robert L Preston Caroline M Bending Gary D 2009 Sequestration of soil nitrogen as tannin protein complexes may improve the competitive ability of sheep laurel Kalmia angustifolia relative to black spruce Picea mariana New Phytologist 181 1 187 98 doi 10 1111 j 1469 8137 2008 02622 x PMID 18811620 Fierer Noah Schimel Joshua P Cates Rex G Zou Jiping 2001 Influence of balsam poplar tannin fractions on carbon and nitrogen dynamics in Alaskan taiga floodplain soils Soil Biology and Biochemistry 33 12 13 1827 39 doi 10 1016 S0038 0717 01 00111 0 Retrieved 18 July 2021 Peng Xinhua Horn Rainer 2007 Anisotropic shrinkage and swelling of some organic and inorganic soils European Journal of Soil Science 58 1 98 107 doi 10 1111 j 1365 2389 2006 00808 x Wang Yang Amundson Ronald Trumbmore Susan 1996 Radiocarbon dating of soil organic matter PDF Quaternary Research 45 3 282 88 Bibcode 1996QuRes 45 282W doi 10 1006 qres 1996 0029 Retrieved 18 July 2021 Brodowski Sonja Amelung Wulf Haumaier Ludwig Zech Wolfgang 2007 Black carbon contribution to stable humus in German arable soils Geoderma 139 1 2 220 28 Bibcode 2007Geode 139 220B doi 10 1016 j geoderma 2007 02 004 Retrieved 18 July 2021 Criscuoli Irene Alberti Giorgio Baronti Silvia Favilli Filippo Martinez Cristina Calzolari Costanza Pusceddu Emanuela Rumpel Cornelia Viola Roberto Miglietta Franco 2014 Carbon sequestration and fertility after centennial time scale incorporation of charcoal into soil PLOS ONE 9 3 e91114 Bibcode 2014PLoSO 991114C doi 10 1371 journal pone 0091114 PMC 3948733 PMID 24614647 Kim Dong Jim Vargas Rodrigo Bond Lamberty Ben Turetsky Merritt R 2012 Effects of soil rewetting and thawing on soil gas fluxes a review of current literature and suggestions for future research Biogeosciences 9 7 2459 83 Bibcode 2012BGeo 9 2459K doi 10 5194 bg 9 2459 2012 Retrieved 3 October 2021 Wagai Rota Mayer Lawrence M Kitayama Kanehiro Knicker Heike 2008 Climate and parent material controls on organic matter storage in surface soils a three pool density separation approach Geoderma 147 1 2 23 33 Bibcode 2008Geode 147 23W doi 10 1016 j geoderma 2008 07 010 hdl 10261 82461 Retrieved 25 July 2021 Minayeva Tatiana Y Trofimov Sergey Ya Chichagova Olga A Dorofeyeva E I Sirin Andrey A Glushkov Igor V Mikhailov N D Kromer Bernd 2008 Carbon accumulation in soils of forest and bog ecosystems of southern Valdai in the Holocene Biology Bulletin 35 5 524 32 doi 10 1134 S1062359008050142 S2CID 40927739 Retrieved 25 July 2021 Vitousek Peter M Sanford Robert L 1986 Nutrient cycling in moist tropical forest Annual Review of Ecology and Systematics 17 137 67 doi 10 1146 annurev es 17 110186 001033 Retrieved 25 July 2021 Rumpel Cornelia Chaplot Vincent Planchon Olivier Bernadou J Valentin Christian Mariotti Andre 2006 Preferential erosion of black carbon on steep slopes with slash and burn agriculture Catena 65 1 30 40 doi 10 1016 j catena 2005 09 005 Retrieved 25 July 2021 a b Paul Eldor A Paustian Keith H Elliott E T Cole C Vernon 1997 Soil organic matter in temperate agroecosystems long term experiments in North America Boca Raton Florida CRC Press p 80 ISBN 978 0 8493 2802 2 Horizons Soils of Canada Archived from the original on 22 September 2019 Retrieved 1 August 2021 Frouz Jan Prach Karel Pizl Vaclav Hanel Ladislav Stary Josef Tajovsky Karel Materna Jan Balik Vladimir Kalcik Jiri Rehounkova Klara 2008 Interactions between soil development vegetation and soil fauna during spontaneous succession in post mining sites European Journal of Soil Biology 44 1 109 21 doi 10 1016 j ejsobi 2007 09 002 Retrieved 1 August 2021 Kabala Cezary Zapart Justyna 2012 Initial soil development and carbon accumulation on moraines of the rapidly retreating Werenskiold Glacier SW Spitsbergen Svalbard archipelago Geoderma 175 176 9 20 Bibcode 2012Geode 175 9K doi 10 1016 j geoderma 2012 01 025 Retrieved 1 August 2021 Ugolini Fiorenzo C Dahlgren Randy A 2002 Soil development in volcanic ash PDF Global Environmental Research 6 2 69 81 Retrieved 1 August 2021 Huggett Richard J 1998 Soil chronosequences soil development and soil evolution a critical review Catena 32 3 155 72 doi 10 1016 S0341 8162 98 00053 8 Retrieved 1 August 2021 De Alba Saturnio Lindstrom Michael Schumacher Thomas E Malo Douglas D 2004 Soil landscape evolution due to soil redistribution by tillage a new conceptual model of soil catena evolution in agricultural landscapes Catena 58 1 77 100 doi 10 1016 j catena 2003 12 004 Retrieved 1 August 2021 Phillips Jonathan D Marion Daniel A 2004 Pedological memory in forest soil development PDF Forest Ecology and Management 188 1 363 80 doi 10 1016 j foreco 2003 08 007 Retrieved 1 August 2021 Mitchell Edward A D Van der Knaap Willem O Van Leeuwen Jacqueline F N Buttler Alexandre Warner Barry G Gobat Jean Michel 2001 The palaeoecological history of the Praz Rodet bog Swiss Jura based on pollen plant macrofossils and testate amoebae Protozoa The Holocene 11 1 65 80 Bibcode 2001Holoc 11 65M doi 10 1191 095968301671777798 S2CID 131032169 Retrieved 1 August 2021 Carcaillet Christopher 2001 Soil particles reworking evidences by AMS 14C dating of charcoal Comptes Rendus de l Academie des Sciences Serie IIA 332 1 21 28 doi 10 1016 S1251 8050 00 01485 3 Retrieved 1 August 2021 Retallack Gregory J 1991 Untangling the effects of burial alteration and ancient soil formation Annual Review of Earth and Planetary Sciences 19 1 183 206 Bibcode 1991AREPS 19 183R doi 10 1146 annurev ea 19 050191 001151 Retrieved 1 August 2021 Bakker Martha M Govers Gerard Jones Robert A Rounsevell Mark D A 2007 The effect of soil erosion on Europe s crop yields Ecosystems 10 7 1209 19 doi 10 1007 s10021 007 9090 3 Uselman Shauna M Qualls Robert G Lilienfein Juliane 2007 Contribution of root vs leaf litter to dissolved organic carbon leaching through soil Soil Science Society of America Journal 71 5 1555 63 Bibcode 2007SSASJ 71 1555U doi 10 2136 sssaj2006 0386 Retrieved 8 August 2021 Schulz Stefanie Brankatschk Robert Dumig Alexander Kogel Knabner Ingrid Schloter Michae Zeyer Josef 2013 The role of microorganisms at different stages of ecosystem development for soil formation Biogeosciences 10 6 3983 96 Bibcode 2013BGeo 10 3983S doi 10 5194 bg 10 3983 2013 Gillet Servane Ponge Jean Francois 2002 Humus forms and metal pollution in soil European Journal of Soil Science 53 4 529 39 doi 10 1046 j 1365 2389 2002 00479 x Retrieved 8 August 2021 Bardy Marion Fritsch Emmanuel Derenne Sylvie Allard Thierry do Nascimento Nadia Regina Bueno Guilherme 2008 Micromorphology and spectroscopic characteristics of organic matter in waterlogged podzols of the upper Amazon basin Geoderma 145 3 222 30 Bibcode 2008Geode 145 222B CiteSeerX 10 1 1 455 4179 doi 10 1016 j geoderma 2008 03 008 Retrieved 8 August 2021 Dokuchaev Vasily Vasilyevich 1967 Russian Chernozem Jerusalem Israel Israel Program for Scientific Translations Retrieved 15 August 2021 IUSS Working Group WRB 2015 World Reference Base for Soil Resources 2014 international soil classification system for naming soils and creating legends for soil maps update 2015 PDF Rome Italy Food and Agriculture Organization ISBN 978 92 5 108370 3 Retrieved 15 August 2021 AlShrouf Ali 2017 Hydroponics aeroponic and aquaponic as compared with conventional farming American Scientific Research Journal for Engineering Technology and Sciences 27 1 247 55 Retrieved 15 August 2021 Leake Simon Haege Elke 2014 Soils for landscape development selection specification and validation Clayton Victoria Australia CSIRO Publishing ISBN 978 0643109650 Pan Xian Zhang Zhao Qi Guo 2007 Measurement of urbanization process and the paddy soil loss in Yixing city China between 1949 and 2000 PDF Catena 69 1 65 73 doi 10 1016 j catena 2006 04 016 Retrieved 15 August 2021 Kopittke Peter M Menzies Neal W Wang Peng McKenna Brigid A Lombi Enzo 2019 Soil and the intensification of agriculture for global food security Environment International 132 105078 doi 10 1016 j envint 2019 105078 ISSN 0160 4120 PMID 31400601 Sturck Julia Poortinga Ate Verburg Peter H 2014 Mapping ecosystem services the supply and demand of flood regulation services in Europe PDF Ecological Indicators 38 198 211 doi 10 1016 j ecolind 2013 11 010 Retrieved 15 August 2021 Van Cuyk Sheila Siegrist Robert Logan Andrew Masson Sarah Fischer Elizabeth Figueroa Linda 2001 Hydraulic and purification behaviors and their interactions during wastewater treatment in soil infiltration systems Water Research 35 4 953 64 doi 10 1016 S0043 1354 00 00349 3 PMID 11235891 Retrieved 15 August 2021 Jeffery Simon Gardi Ciro Arwyn Jones 2010 European atlas of soil biodiversity Luxembourg Luxembourg Publications Office of the European Union doi 10 2788 94222 ISBN 978 92 79 15806 3 Retrieved 15 August 2021 De Deyn Gerlinde B Van der Putten Wim H 2005 Linking aboveground and belowground diversity Trends in Ecology and Evolution 20 11 625 33 doi 10 1016 j tree 2005 08 009 PMID 16701446 Retrieved 15 August 2021 Hansen James Sato Makiko Kharecha Pushker Beerling David Berner Robert Masson Delmotte Valerie Pagani Mark Raymo Maureen Royer Dana L Zachos James C 2008 Target atmospheric CO2 where should humanity aim PDF Open Atmospheric Science Journal 2 1 217 31 arXiv 0804 1126 Bibcode 2008OASJ 2 217H doi 10 2174 1874282300802010217 S2CID 14890013 Retrieved 22 August 2021 Lal Rattan 11 June 2004 Soil carbon sequestration impacts on global climate change and food security PDF Science 304 5677 1623 27 Bibcode 2004Sci 304 1623L doi 10 1126 science 1097396 PMID 15192216 S2CID 8574723 Retrieved 22 August 2021 Blakeslee Thomas 24 February 2010 Greening deserts for carbon credits Orlando Florida USA Renewable Energy World Archived from the original on 1 November 2012 Retrieved 22 August 2021 Mondini Claudio Contin Marco Leita Liviana De Nobili Maria 2002 Response of microbial biomass to air drying and rewetting in soils and compost Geoderma 105 1 2 111 24 Bibcode 2002Geode 105 111M doi 10 1016 S0016 7061 01 00095 7 Retrieved 22 August 2021 Peatlands and farming Stoneleigh United Kingdom National Farmers Union of England and Wales 6 July 2020 Retrieved 22 August 2021 van Winden Julia F Reichart Gert Jan McNamara Niall P Benthien Albert Sinninghe Damste Jaap S 2012 Temperature induced increase in methane release from peat bogs a mesocosm experiment PLoS ONE 7 6 e39614 Bibcode 2012PLoSO 739614V doi 10 1371 journal pone 0039614 PMC 3387254 PMID 22768100 Davidson Eric A Janssens Ivan A 2006 Temperature sensitivity of soil carbon decomposition and feedbacks to climate change PDF Nature 440 7081 165 73 Bibcode 2006Natur 440 165D doi 10 1038 nature04514 PMID 16525463 S2CID 4404915 Retrieved 22 August 2021 Abrahams Pter W 1997 Geophagy soil consumption and iron supplementation in Uganda Tropical Medicine and International Health 2 7 617 23 doi 10 1046 j 1365 3156 1997 d01 348 x PMID 9270729 S2CID 19647911 Setz Eleonore Zulnara Freire Enzweiler Jacinta Solferini Vera Nisaka Amendola Monica Pimenta Berton Ronaldo Severiano 1999 Geophagy in the golden faced saki monkey Pithecia pithecia chrysocephala in the Central Amazon Journal of Zoology 247 1 91 103 doi 10 1111 j 1469 7998 1999 tb00196 x Retrieved 22 August 2021 Kohne John Maximilian Koehne Sigrid Simunek Jirka 2009 A review of model applications for structured soils a Water flow and tracer transport PDF Journal of Contaminant Hydrology 104 1 4 4 35 Bibcode 2009JCHyd 104 4K CiteSeerX 10 1 1 468 9149 doi 10 1016 j jconhyd 2008 10 002 PMID 19012994 Archived PDF from the original on 7 November 2017 Retrieved 22 August 2021 Diplock Elizabeth E Mardlin Dave P Killham Kenneth S Paton Graeme Iain 2009 Predicting bioremediation of hydrocarbons laboratory to field scale Environmental Pollution 157 6 1831 40 doi 10 1016 j envpol 2009 01 022 PMID 19232804 Retrieved 22 August 2021 Moeckel Claudia Nizzetto Luca Di Guardo Antonio Steinnes Eiliv Freppaz Michele Filippa Gianluca Camporini Paolo Benner Jessica Jones Kevin C 2008 Persistent organic pollutants in boreal and montane soil profiles distribution evidence of processes and implications for global cycling Environmental Science and Technology 42 22 8374 80 Bibcode 2008EnST 42 8374M doi 10 1021 es801703k PMID 19068820 Retrieved 22 August 2021 Rezaei Khalil Guest Bernard Friedrich Anke Fayazi Farajollah Nakhaei Mohamad Aghda Seyed Mahmoud Fatemi Beitollahi Ali 2009 Soil and sediment quality and composition as factors in the distribution of damage at the December 26 2003 Bam area earthquake in SE Iran M s 6 6 Journal of Soils and Sediments 9 23 32 doi 10 1007 s11368 008 0046 9 S2CID 129416733 Retrieved 22 August 2021 Johnson Dan L Ambrose Stanley H Bassett Thomas J Bowen Merle L Crummey Donald E Isaacson John S Johnson David N Lamb Peter Saul Mahir Winter Nelson Alex E 1997 Meanings of environmental terms Journal of Environmental Quality 26 3 581 89 doi 10 2134 jeq1997 00472425002600030002x Retrieved 29 August 2021 Oldeman L Roel 1993 Global extent of soil degradation ISRIC Bi Annual Report 1991 1992 Wageningen The Netherlands International Soil Reference and Information Centre ISRIC pp 19 36 Retrieved 29 August 2021 Sumner Malcolm E Noble Andrew D 2003 Soil acidification the world story PDF In Rengel Zdenko ed Handbook of soil acidity New York NY USA Marcel Dekker pp 1 28 Retrieved 29 August 2021 Karam Jean Nicell James A 1997 Potential applications of enzymes in waste treatment Journal of Chemical Technology amp Biotechnology 69 2 141 53 doi 10 1002 SICI 1097 4660 199706 69 2 lt 141 AID JCTB694 gt 3 0 CO 2 U Retrieved 5 September 2021 Sheng Guangyao Johnston Cliff T Teppen Brian J Boyd Stephen A 2001 Potential contributions of smectite clays and organic matter to pesticide retention in soils Journal of Agricultural and Food Chemistry 49 6 2899 2907 doi 10 1021 jf001485d PMID 11409985 Retrieved 5 September 2021 Sprague Lori A Herman Janet S Hornberger George M Mills Aaron L 2000 Atrazine adsorption and colloid facilitated transport through the unsaturated zone PDF Journal of Environmental Quality 29 5 1632 41 doi 10 2134 jeq2000 00472425002900050034x Retrieved 5 September 2021 Ballabio Cristiano Panagos Panos Lugato Emanuele Huang Jen How Orgiazzi Alberto Jones Arwyn Fernandez Ugalde Oihane Borrelli Pasquale Montanarella Luca 15 September 2018 Copper distribution in European topsoils an assessment based on LUCAS soil survey Science of the Total Environment 636 282 98 Bibcode 2018ScTEn 636 282B doi 10 1016 j scitotenv 2018 04 268 ISSN 0048 9697 PMID 29709848 Le Houerou Henry N 1996 Climate change drought and desertification PDF Journal of Arid Environments 34 2 133 85 Bibcode 1996JArEn 34 133L doi 10 1006 jare 1996 0099 Retrieved 5 September 2021 Lyu Yanli Shi Peijun Han Guoyi Liu Lianyou Guo Lanlan Hu Xia Zhang Guoming 2020 Desertification control practices in China Sustainability 12 8 3258 doi 10 3390 su12083258 ISSN 2071 1050 Kefi Sonia Rietkerk Max Alados Concepcion L Pueyo Yolanda Papanastasis Vasilios P El Aich Ahmed de Ruiter Peter C 2007 Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems Nature 449 7159 213 217 Bibcode 2007Natur 449 213K doi 10 1038 nature06111 hdl 1874 25682 PMID 17851524 S2CID 4411922 Retrieved 5 September 2021 Wang Xunming Yang Yi Dong Zhibao Zhang Caixia 2009 Responses of dune activity and desertification in China to global warming in the twenty first century Global and Planetary Change 67 3 4 167 85 Bibcode 2009GPC 67 167W doi 10 1016 j gloplacha 2009 02 004 Retrieved 5 September 2021 Yang Dawen Kanae Shinjiro Oki Taikan Koike Toshio Musiake Katumi 2003 Global potential soil erosion with reference to land use and climate changes PDF Hydrological Processes 17 14 2913 28 Bibcode 2003HyPr 17 2913Y doi 10 1002 hyp 1441 Retrieved 5 September 2021 Sheng Jian an Liao An zhong 1997 Erosion control in South China Catena 29 2 211 21 doi 10 1016 S0341 8162 96 00057 4 ISSN 0341 8162 Retrieved 5 September 2021 Ran Lishan Lu Xi Xi Xin Zhongbao 2014 Erosion induced massive organic carbon burial and carbon emission in the Yellow River basin China PDF Biogeosciences 11 4 945 59 Bibcode 2014BGeo 11 945R doi 10 5194 bg 11 945 2014 hdl 10722 228184 Retrieved 5 September 2021 Verachtert Els Van den Eeckhaut Miet Poesen Jean Deckers Jozef 2010 Factors controlling the spatial distribution of soil piping erosion on loess derived soils a case study from central Belgium Geomorphology 118 3 339 48 Bibcode 2010Geomo 118 339V doi 10 1016 j geomorph 2010 02 001 Retrieved 5 September 2021 Jones Anthony 1976 Soil piping and stream channel initiation Water Resources Research 7 3 602 10 Bibcode 1971WRR 7 602J doi 10 1029 WR007i003p00602 Retrieved 5 September 2021 Dooley Alan June 2006 Sandboils 101 Corps has experience dealing with common flood danger Engineer Update US Army Corps of Engineers Archived from the original on 18 April 2008 Oosterbaan Roland J 1988 Effectiveness and social environmental impacts of irrigation projects a critical review PDF Annual Reports of the International Institute for Land Reclamation and Improvement ILRI Wageningen The Netherlands pp 18 34 Archived PDF from the original on 19 February 2009 Retrieved 5 September 2021 Drainage manual a guide to integrating plant soil and water relationships for drainage of irrigated lands PDF Washington D C United States Department of the Interior Bureau of Reclamation 1993 ISBN 978 0 16 061623 5 Retrieved 5 September 2021 Oosterbaan Roland J Waterlogging soil salinity field irrigation plant growth subsurface drainage groundwater modelling surface runoff land reclamation and other crop production and water management aspects Archived from the original on 16 August 2010 Retrieved 5 September 2021 Stuart Alexander M Pame Anny Ruth P Vithoonjit Duangporn Viriyangkura Ladda Pithuncharurnlap Julmanee Meesang Nisa Suksiri Prarthana Singleton Grant R Lampayan Rubenito M 2018 The application of best management practices increases the profitability and sustainability of rice farming in the central plains of Thailand Field Crops Research 220 78 87 doi 10 1016 j fcr 2017 02 005 Retrieved, wikipedia, wiki, book,

books

, library,

article

, read, download, free, free download, mp3, video, mp4, 3gp, jpg, jpeg, gif, png, picture, music, song, movie, book, game, games.