Editing Soil (section)

== Composition ==
[[File:Estructura-suelo.jpg|thumb|alt= This is a diagram and related photograph of soil layers from bedrock to soil.|A, B, and C represent the [[soil horizon|soil profile]], a notation firstly coined by [[Vasily Dokuchaev]] (1846–1903), the father of pedology. Here, A is the [[topsoil]]; B is a [[regolith]]; C is a [[saprolite]] (a less-weathered regolith); the bottom-most layer represents the [[bedrock]].]]
{{Pie chart
|caption = Components of a silt loam soil by percent volume
|value1 = 25
|label1 = Water
|color1 = blue
|value2 = 25
|label2 = Gases
|color2 = cyan
|value3 = 18
|label3 = Sand
|color3 = yellow
|value4 = 18
|label4 = Silt
|color4 = brown
|value5 = 9
|label5 = Clay
|color5 = grey
|value6 = 5
|label6 = Organic matter
|color6 = black
}}

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.<ref name="McClellan2017">{{cite web |last=McClellan |first=Tai |title=Soil composition |url=https://www.ctahr.hawaii.edu/mauisoil/a_comp.aspx |publisher=[[University of Hawaiʻi]] at Mānoa, College of Tropical Agriculture and Human Resources |access-date=5 January 2025 }}</ref> 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.<ref>{{cite book |last=Zhang |first=Hailin |title=Master Gardener's Manual |chapter-url=https://extension.okstate.edu/fact-sheets/print-publications/e/master-gardeners-handbook-e-1034.pdf |chapter=Soils and fertilizer |pages=54–63 |publisher=Oklahoma Cooperative Extension, Service Division of Agricultural Sciences and Natural Resources, [[Oklahoma State University]] |location=Stillwater, Oklahoma |access-date=5 January 2025 }}</ref> The [[pore space]] allows for the infiltration and movement of air and water, both of which are critical for life existing in soil.<ref name="Vannier1987">{{cite journal |last=Vannier |first=Guy |journal=Biology and Fertility of Soils |volume=3 |issue=1 |title=The porosphere as an ecological medium emphasized in Professor Ghilarov's work on soil animal adaptations |year=1987 |url=https://fr.1lib.sk/book/37554227/660688 |pages=39–44 |doi=10.1007/BF00260577 |bibcode=1987BioFS...3...39V |s2cid=297400 |access-date=5 January 2025 }}</ref> [[Soil compaction|Compaction]], a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms.<ref>{{cite journal |last1=Torbert |first1=H. Allen |last2=Wood |first2=Wes |journal=Communications in Soil Science and Plant Analysis |volume=23 |issue=11 |title=Effect of soil compaction and water-filled pore space on soil microbial activity and N losses |year=1992 |url=https://www.researchgate.net/publication/240546132 |pages=1321‒31 |doi=10.1080/00103629209368668 |bibcode=1992CSSPA..23.1321T |access-date=5 January 2025 }}</ref>

Given sufficient time, an undifferentiated soil will evolve a [[soil horizon|soil profile]] that consists of two or more layers, referred to as [[Soil horizon|soil horizons]]. These differ in one or more properties such as in their [[Soil texture|texture]], [[structure]], [[density]], [[porosity]], [[Viscosity|consistency]], temperature, color, and [[Reactivity (chemistry)|reactivity]].<ref name="Buol"/> 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|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.{{sfn|Simonson|1957|p=17}} 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).<ref>{{cite journal |last1=Zanella |first1=Augusto |last2=Katzensteiner |first2=Klaus |last3=Ponge |first3=Jean-François |last4=Jabiol |first4=Bernard |last5=Sartori |first5=Giacomo |last6=Kolb |first6=Eckart |last7=Le Bayon |first7=Renée-Claire |last8=Aubert |first8=Michaël |last9=Ascher-Jenull |first9=Judith |last10=Englisch |first10=Michael |last11=Hager |first11=Herbert |title=TerrHum: an iOS App for classifying terrestrial humipedons and some considerations about soil classification |journal=[[Soil Science Society of America Journal]] |date=June 2019 |volume=83 |issue=S1 |pages=S42–S48 |doi=10.2136/sssaj2018.07.0279 |s2cid=197555747 |url=https://www.researchgate.net/publication/332080061 |access-date=5 January 2025 }}</ref>

The soil texture is determined by the relative proportions of the individual particles of [[sand]], [[silt]], and [[clay]] that make up the soil. [[File:SoilTextureTriangle.svg|thumb|A [[Soil triangle|soil texture triangle]] plot is a visual representation of the proportions of sand, silt, and clay in a soil sample.]] The interaction of the individual mineral particles with organic matter, water, gases via [[Biotic component|biotic]] and [[abiotic]] processes causes those particles to [[flocculate]] (stick together) to form [[soil structure|aggregates]] or [[ped]]s.<ref name="Bronick2005">{{cite journal |last1=Bronick |first1=Carol J. |last2=Lal |first2=Ratan |title=Soil structure and management: a review |journal=Geoderma |date=January 2005 |volume=124 |issue=1–2 |pages=3–22 |doi=10.1016/j.geoderma.2004.03.005 |url=https://www.academia.edu/72307009 |access-date=5 January 2025 |bibcode=2005Geode.124....3B }}</ref> 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.<ref>{{cite web |url=https://www.fao.org/3/r4082e/r4082e03.htm |title=Soil and water |website=[[Food and Agriculture Organization of the United Nations]] |access-date=12 January 2025 }}</ref> 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 (chemistry)|dissolution]], [[Precipitation (chemistry)|precipitation]] and [[Leaching (agriculture)|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.<ref>{{cite journal |last1=Valentin |first1=Christian |last2=d'Herbès |first2=Jean-Marc |last3=Poesen |first3=Jean |journal=Catena |volume=37 |issue=1 |title=Soil and water components of banded vegetation patterns |year=1999 |url=https://www.academia.edu/35300713 |pages=1‒24 |doi=10.1016/S0341-8162(99)00053-3 |bibcode=1999Caten..37....1V |access-date=12 January 2025 }}</ref>

Soils supply [[plant]]s with [[nutrient]]s, most of which are held in place by particles of [[Soil texture#Soil separates|clay]] and organic matter ([[colloid]]s)<ref>{{cite book |last1=Brady |first1=Nyle C. |last2=Weil |first2=Ray R. |date=2007 |chapter=The colloidal fraction: seat of soil chemical and physical activity |title=The nature and properties of soils |pages=310–357 |edition=14th |editor-last1=Brady |editor-first1=Nyle C. |editor-last2=Weil |editor-first2=Ray R. |publisher=[[Pearson Education|Pearson]] |location=London, United Kingdom |isbn=978-0132279383 |chapter-url=https://www.researchgate.net/publication/309630422 |access-date=12 January 2025 }}</ref> The nutrients may be [[Adsorption|adsorbed]] on clay mineral surfaces, bound within clay minerals ([[Absorption (chemistry)|absorbed]]), or bound within organic compounds as part of the living [[Soil organism|organisms]] or dead soil organic matter. These bound nutrients interact with soil water to [[Buffer solution|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.<ref>{{cite web |url=http://eagri.org/eagri50/SSAC121/lec14.pdf |title=Soil colloids: properties, nature, types and significance |website=[[Tamil Nadu Agricultural University]] |access-date=12 January 2025 }}</ref>

Plant nutrient availability is affected by [[soil pH]], which is a measure of the [[hydrogen]] [[Thermodynamic activity|ion activity]] in the soil solution. Soil pH is a function of many soil forming factors, and is generally lower (more acidic) where weathering is more advanced.<ref>{{cite web |url=https://www.researchgate.net/publication/305775103 |last=Miller |first=Jarrod Ottis |title=Soil pH affects nutrient availability |access-date=12 January 2025 }}</ref>

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]],<ref>{{cite journal |last1=Goulding |first1=Keith W.T. |last2=Bailey |first2=Neal J. |last3=Bradbury |first3=Nicola J. |last4=Hargreaves |first4=Patrick |last5=Howe |first5=M.T. |last6=Murphy |first6=Daniel V. |last7=Poulton |first7=Paul R. |last8=Willison |first8=Toby W. |journal=[[New Phytologist]] |volume=139 |issue=1 |title=Nitrogen deposition and its contribution to nitrogen cycling and associated soil processes |year=1998 |pages=49‒58 |doi=10.1046/j.1469-8137.1998.00182.x |doi-access=free |bibcode=1998NewPh.139...49G }}</ref> 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]].<ref>{{cite book |last=Kononova |first=M.M. |date=1966 |title=Soil organic matter: its nature, its role in soil formation and in soil fertility |edition=2nd |publisher=[[Elsevier]] |location=Amsterdam, the Netherlands |isbn=978-1-4831-8568-2 |url=https://fr.1lib.sk/book/2275488/56c210 |access-date=19 January 2025 |archive-date=22 March 2023 |archive-url=https://web.archive.org/web/20230322091500/https://fr1lib.org/book/2275488/ea4395 |url-status=live }}</ref> Microbial [[soil enzyme]]s 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.<ref>{{cite journal |last1=Burns |first1=Richards G. |last2=DeForest |first2=Jared L. |last3=Marxsen |first3=Jürgen |last4=Sinsabaugh |first4=Robert L. |last5=Stromberger |first5=Mary E. |last6=Wallenstein |first6=Matthew D. |last7=Weintraub |first7=Michael N. |last8=Zoppini |first8=Annamaria |journal=[[Soil Biology and Biochemistry]] |volume=58 |title=Soil enzymes in a changing environment: current knowledge and future directions |year=2013 |pages=216‒34 |doi=10.1016/j.soilbio.2012.11.009 |bibcode=2013SBiBi..58..216B |url=https://www.academia.edu/25235991 |access-date=19 January 2025 }}</ref>