Plant nutrients in soil

{{Short description|Nutrient within the soil}} Sixteen 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), and chlorine (Cl).<ref>{{cite book |last=Pandey |first=Nalini |chapter=Role of plant nutrients in plant growth and physiology |doi=10.1007/978-981-10-9044-8_2 |pages=51–93 |title=Plant nutrients and abiotic stress tolerance |editor-last1=Hasanuzzaman |editor-first1=Mirza |editor-last2=Fujita |editor-first2=Masayuki |editor-last3=Oku |editor-first3=Hirosuke |editor-last4=Nahar |editor-first4=Kamrun |editor-last5=Hawrylak-Nowak |editor-first5=Barbara |year=2018 |publisher=Springer Nature Singapore |location=Singapore, Singapore |chapter-url=https://z-library.ec/book/Jy1e0bpAyz |isbn=978-981-10-9044-8 |access-date=5 May 2026 }}</ref> 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, although some of them, such as silicon (Si), have been shown to improve nutrient availability,<ref>{{cite journal |last1=Pavlovic |first1=Jelena |last2=Kostic |first2=Ljiljana |last3=Bosnic |first3=Predrag |last4=Kirkby |first4=Ernest A. |last5=Nikolic |first5=Miroslav |year=2021 |title=Interactions of silicon with essential and beneficial elements in plants |journal=Frontiers in Plant Science |volume=12 |issue=697592 |pages=1–19 |doi=10.3389/fpls.2021.697592 |doi-access=free |pmid=34249069 |pmc=8261142 }}</ref> hence the use of stinging nettle and horsetail (both silica-rich) macerations in biodynamic agriculture.<ref>{{cite journal |last1=Pairault |first1=Liliana-Adriana |last2=Tritean |first2=Naomi |last3=Constantinescu-Aruxandei |first3=Diana |last4=Oancea |first4=Florin |year=2022 |title=Plant biostimulants based on nanoformulated biosilica recovered from silica-rich biomass |journal=Scientific Bulletin, Series F, Biotechnologies |volume=26 |issue=1 |pages=49–58 |url=https://biotechnologyjournal.usamv.ro/pdf/2022/issue_1/Art6.pdf |access-date=5 May 2026 }}</ref> 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.<ref>{{cite web |last1=Singh |first1=Balwant |last2=Schulze |first2=Darrell G. |date=23 November 2018 |title=Soil minerals and plant nutrition |website=www.thcfarmer.com |url=https://www.thcfarmer.com/threads/soil-minerals-and-plant-nutrition.101060/ |access-date=5 May 2026 }}</ref> The Liebig's 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 because of stoichiometry constraints.<ref>{{cite journal |last1=Van der Ploeg |first1=Rienk R. |last2=Böhm |first2=Wolfgang |last3=Kirkham |first3=Mary Beth |date=September 1999 |title=On the origin of the theory of mineral nutrition of plants and the Law of the Minimum |journal=Soil Science Society of America Journal |volume=63 |issue=5 |pages=1055–62 |doi=10.2136/sssaj1999.6351055x |citeseerx=10.1.1.475.7392 |bibcode=1999SSASJ..63.1055V |doi-access=free }}</ref> 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.<ref>{{cite journal |last1=Knecht |first1=Magnus F. |last2=Göransson |first2=Anders |year=2004 |title=Terrestrial plants require nutrients in similar proportions |journal=Tree Physiology |volume=24 |issue=4 |pages=447–60 |doi=10.1093/treephys/24.4.447 |pmid=14757584 |url=https://z-library.ec/book/7y3NY4Bx9J |access-date=5 May 2026 }}</ref>

Plant uptake of nutrients can only proceed when they are present in a plant-available form.<ref>{{cite book |last1=Fageria |first1=Nand Kumar |last2=Baligar |first2=V. C. |chapter=Nutrient availability |title=Encyclopedia of soils in the environment |editor-last=Hillel |editor-first=Daniel |year=2005 |publisher=Elsevier |location=Amsterdam, The Netherlands |chapter-url=https://www.academia.edu/39377592 |pages=63–71 |isbn=978-0-12-348530-4 |access-date=5 May 2026 }}</ref> In most situations, nutrients are absorbed from the soil water in an ionic form by diffusion, mass transport, and root interception.<ref name="Reichardt2020">{{cite book |last1=Reichardt |first1=Klaus |last2=Timm |first2=Luís Carlos |chapter=How plants absorb nutrients from the soil |title=Soil, plant and atmosphere: concepts, processes and applications |editor-last1=Reichardt |editor-first1=Klaus |editor-last2=Timm |editor-first2=Luís Carlos |year=2020 |publisher=Springer Nature Switzerland |location=Cham, Switzerland |chapter-url=https://archive.org/details/reichardt-timm-2020 |isbn=978-3-030-19322-5 |doi=10.1007/978-3-030-19322-5_16 |pages=313–30 |access-date=5 May 2026 }}</ref> 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.<ref>{{cite journal |last=Manning |first=David A. C. |year=2010 |title=Mineral sources of potassium for plant nutrition: a review |journal=Agronomy for Sustainable Development |volume=30 |issue=2 |pages=281–94 |doi=10.1051/agro/2009023 |url=https://z-library.ec/book/Z9kWgAva9O |access-date=5 May 2026 }}</ref> However, the association of plant roots with mycorrhizal fungal partners increases the dissolution rate of phosphorus-containing apatite.<ref>{{cite journal |last1=Smits |first1=Mark M. |last2=Bonneville |first2=Steeve |last3=Benning |first3=Liane G. |last4=Banwart |first4=Steven A. |last5=Leake |first5=Jonathan R. |date=September 2012 |title=Plant-driven weathering of apatite: the role of an ectomycorrhizal fungus |journal=Geobiology |volume=10 |issue=5 |pages=445–56 |doi=10.1111/j.1472-4669.2012.00331.x |url=https://www.researchgate.net/publication/225042941 |access-date=5 May 2026 }}</ref>

The nutrients adsorbed in an exchangeable form onto the surfaces of clay colloids and soil organic matter (the soil matrix) provide a more accessible reservoir of many plant nutrients (e.g. K, Ca, Mg, P, Zn).<ref>{{cite book |last1=Bolt |first1=G. H. |last2=Bruggenwert |first2=M. G. M. |last3=Kamphorst |first3=Arie |chapter=Adsorption of cations by soil |title=Soil chemistry. A. Basic elements |editor-last1=Bolt |editor-first1=G. H. |editor-last2=Bruggenwert |editor-first2=M. G. M. |year=1976 |series=Developments in soil science |volume=5 |publisher=Elsevier |location=Amsterdam, The Netherlands |chapter-url=https://z-library.ec/book/mX4N452b9x |isbn=978-0-444-41435-9 |doi=10.1016/S0166-2481(08)70633-0 |pages=54–90 |access-date=6 May 2026 }}</ref> As plants absorb the nutrients from the soil water, the soluble pool is replenished (exchanged) from the surface-bound pool.<ref>{{cite book |last=Jungk |first=Albrecht O. |chapter=Dynamics of nutrient movement at the soil-root interface |title=Plant roots: the hidden half |edition=3rd |editor-last1=Waisel |editor-first1=Yoav |editor-last2=Eshel |editor-first2=Amram |editor-last3=Beeckman |editor-first3=Tom |editor-last4=Kafkafi |editor-first4=Uzi |year=2002 |publisher=CRC Press |location=Boca Raton, Florida |chapter-url=https://z-library.ec/book/mLB4x6Gryz |isbn=9780429221859 |doi=10.1201/9780203909423.CH35 |pages=587–616 |access-date=6 May 2026 }}</ref> 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.<ref name="Roy2006">{{cite book |chapter-url=https://www.fao.org/fileadmin/templates/soilbiodiversity/Downloadable_files/fpnb16.pdf |title=Plant nutrition for food security: a guide for integrated nutrient management |last1=Roy |first1=R. N. |last2=Finck |first2=Arnold |last3=Blair |first3=Graeme J. |last4=Tandon |first4=Hari Lal Singh |publisher=Food and Agriculture Organization of the United Nations |location=Rome, Italy |year=2006 |isbn=978-92-5-105490-1 |pages=43–90 |chapter=Soil fertility and crop production |access-date=6 May 2026 }}</ref>

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.<ref>{{cite journal |last1=Parfitt |first1=Roger L. |last2=Giltrap |first2=Donna J. |last3=Whitton |first3=Joe S. |year=1995 |title=Contribution of organic matter and clay minerals to the cation exchange capacity of soil |journal=Communications in Soil Science and Plant Analysis |volume=26 |issue=9–10 |pages=1343–55 |url=https://www.researchgate.net/publication/249073571 |doi=10.1080/00103629509369376 |bibcode=1995CSSPA..26.1343P |access-date=6 May 2026 }}</ref> However, despite the great capacity of humus to retain water once water-soaked, its high hydrophobicity decreases its wettability.<ref>{{cite journal |last1=Hajnos |first1=Mieczyslaw |last2=Jozefaciuk |first2=Grzegorz |last3=Sokołowska |first3=Zofia |last4=Greiffenhagen |first4=Andreas |last5=Wessolek |first5=Gerd |date=October 2003 |title=Water storage, surface, and structural properties of sandy forest humus horizons |journal=Journal of Plant Nutrition and Soil Science |volume=166 |issue=5 |pages=625–34 |url=https://www.researchgate.net/publication/229970348 |doi=10.1002/jpln.200321161 |bibcode=2003JPNSS.166..625H |access-date=6 May 2026 }}</ref> All in all, small amounts of humus may remarkably increase the soil's capacity to promote plant growth.<ref>{{cite book |last1=Nardi |first1=Serenella |last2=Concheri |first2=Gianmaria |last3=Dell'Agnola |first3=Giorgio |chapter=Biological activity of humus |title=Humic substances in terrestrial ecosystems |editor-last=Piccolo |editor-first=Alessandro |year=1996 |publisher=Elsevier |location=Amsterdam, The Netherlands |chapter-url=https://z-library.ec/book/PXzwqgDdL6 |isbn=978-0-444-81516-3 |doi=10.1016/B978-044481516-3/50010-4 |pages=361–406 |access-date=6 May 2026 }}</ref><ref name="Roy2006"/>

{| class="wikitable sortable floatright" |+ Plant nutrients, their chemical symbols, and the ionic forms common in soils and available for plant uptake<ref>{{cite book |url=https://archive.org/details/soilsintroductio00dona/page/124/mode/2up |title=Soils: an introduction to soils and plant growth |edition=4th |last1=Donahue |first1=Roy Luther |last2=Miller |first2=Raymond W. |last3=Shickluna |first3=John C. |publisher=Prentice-Hall |location=Englewood Cliffs, New Jersey |year=1977 |isbn=978-0138219185 |page=125 |access-date=8 May 2026 }}</ref> |- ! Element !! Symbol !! Ion or molecule |- | Carbon || C || CO₂ (mostly through leaf and root litter) |- | 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) |}

==Uptake processes==

Nutrients in the soil are taken up by the plant through its roots, and in particular its root hairs.<ref>{{cite journal |last=Jungk |first=Albrecht |date=April 2001 |title=Root hairs and the acquisition of plant nutrients from soil |journal=Journal of Plant Nutrition and Soil Science |volume=164 |issue=2 |pages=121–9 |url=https://z-library.ec/book/vydEY0m2XV |doi=10.1002/1522-2624(200104)164:2<121::AID-JPLN121>3.0.CO;2-6 |access-date=6 May 2026 }}</ref> To be taken up by a plant, a nutrient element must be located near the root surface; however, the supply of nutrients in contact with the root is rapidly depleted within a distance of ca. 2&nbsp;mm.<ref>{{cite journal |last1=Föhse |first1=Doris |last2=Claassen |first2=Norbert |last3=Jungk |first3=Albrecht |date=April 1991 |title=Phosphorus efficiency of plants. II. Significance of root radius, root hairs and cation-anion balance for phosphorus influx in seven plant species |journal=Plant and Soil |volume=132 |issue=2 |pages=261–72 |url=https://z-library.ec/book/YyVv8meKyp |doi=10.1007/BF00010407 |bibcode=1991PlSoi.132..261F |s2cid=28489187 |access-date=6 May 2026 }}</ref> There are three basic mechanisms whereby nutrient ions dissolved in the soil solution are brought into contact with plant roots:

# Mass flow of water # Diffusion within water # Interception by root growth<ref name="Reichardt2020"/>

All three mechanisms operate simultaneously, but one mechanism or another may be most important for a particular nutrient.<ref>{{cite book |last=Barber |first=Stanley A. |title=Limiting steps in ion uptake by plants from soil |year=1966 |publisher=International Atomic Energy Agency |location=Vienna, Austria |pages=39–45 |chapter=The role of root interception, mass flow and diffusion in regulating the uptake of ions by plants from soil |access-date=6 May 2026 |chapter-url=https://inis.iaea.org/records/25hvn-hyj66/files/25045470.pdf }}</ref> For example, in the case of calcium, which is generally plentiful in the soil solution, except when aluminium over competes calcium on cation exchange sites in very acid soils (pH less than 4),<ref>{{cite journal |last1=Lawrence |first1=Gregory B. |last2=David |first2=Mark B. |last3=Shortle |first3=Walter C. |date=9 November 1995 |title=A new mechanism for calcium loss in forest floor soils |journal=Nature |volume=378 |issue=6553 |pages=162–5 |url=https://www.researchgate.net/publication/32031384 |doi=10.1038/378162a0 |access-date=7 May 2026 |bibcode=1995Natur.378..162L |s2cid=4365594 }}</ref> mass flow alone can usually bring sufficient amounts to the root surface.<ref>{{cite journal |last=Kirkby |first=Ernest A. |year=1979 |title=Maximizing calcium uptake by plants |journal=Communications in Soil Science and Plant Analysis |volume=10 |issue=1–2 |pages=89–113 |url=https://z-library.ec/book/gyxlzBWgyo |doi=10.1080/00103627909366881 |access-date=7 May 2026 }}</ref> However, in the case of phosphorus, diffusion is needed to supplement mass flow.<ref>{{cite journal |last1=Santner |first1=Jakob |last2=Smolders |first2=Erik |last3=Wenzel |first3=Walter W. |last4=Degryse |first4=Fien |date=September 2012 |title=First observation of diffusion-limited plant root phosphorus uptake from nutrient solution |journal=Plant, Cell & Environment |volume=35 |issue=9 |pages=1558–66 |url=https://z-library.ec/book/Jy1Gap0BLz |doi=10.1111/j.1365-3040.2012.02509.x |access-date=6 May 2026 }}</ref> For the most part, nutrient ions must travel some distance in the soil solution to reach the root surface. This movement can take place by mass flow, as when dissolved nutrients are carried along with the soil water flowing toward a root that is actively drawing water from the soil. In this type of movement, the nutrient ions are somewhat analogous to leaves floating down a stream. In addition, nutrient ions continually move by diffusion from areas of greater concentration toward the nutrient-depleted areas of lower concentration around the root surface. That process is due to random motion, also called Brownian motion, of molecules within a gradient of decreasing concentration.<ref>{{cite journal |last=Brinkman |first=Henri Coenraad |year=1956 |title=Brownian motion in a field of force and the diffusion theory of chemical reactions. II |journal=Physica |volume=22 |issue=1–5 |pages=149–55 |url=https://publications.tno.nl/publication/34619749/QX63CA/brinkman-1956-brownian-2.pdf |doi=10.1016/S0031-8914(56)80019-0 |access-date=7 May 2026 }}</ref> By the mean of diffusion, plants can continue to take up nutrients even when transpiration stops following stomatal closure and thus mass flow is interrupted.<ref>{{cite journal |last=Barber |first=Stanley A. |date=January 1962 |title=A diffusion and mass-flow concept of soil nutrient availability |journal=Soil Science |volume=93 |issue=1 |pages=39–49 |url=https://z-library.ec/book/nLAnWZl69z |doi=10.1097/00010694-196201000-00007 |access-date=7 May 2026 }}</ref> Finally, root interception comes into play as roots continually grow into new, undepleted soil.<ref name="Reichardt2020"/> By this way roots are also able to absorb nanomaterials such as nanoparticulate organic matter.<ref>{{cite journal |last1=Lin |first1=Sijie |last2=Reppert |first2=Jason |last3=Hu |first3=Qian |last4=Hudson |first4=Joan S. |last5=Reid |first5=Michelle L. |last6=Ratnikova |first6=Tatsiana A. |last7=Rao |first7=Apparao M. |last8=Luo |first8=Hong |last9=Ke |first9=Pu Chun |date=18 May 2009 |title=Uptake, translocation, and transmission of carbon nanomaterials in rice plants |journal=Small |volume=5 |issue=10 |pages=1128–32 |url=https://www.academia.edu/14826006 |doi=10.1002/smll.200801556 |pmid=19235197 |access-date=7 May 2026 }}</ref>

{| class="wikitable" style="border-spacing: 5px; margin:auto;" |+ Estimated relative importance of mass flow, diffusion and root interception as mechanisms in supplying plant nutrients to corn plant roots in soils<ref>{{cite book |url=https://archive.org/details/soilsintroductio00dona/page/124/mode/2up |title=Soils: an introduction to soils and plant growth |edition=4th |last1=Donahue |first1=Roy Luther |last2=Miller |first2=Raymond W. |last3=Shickluna |first3=John C. |publisher=Prentice-Hall |location=Englewood Cliffs, New Jersey |year=1977 |isbn=978-0138219185 |page=126 |access-date=8 May 2026 }}</ref> |- ! scope="col" style="width:100px;" rowspan="2"| Nutrient ! colspan="3"| Approximate percentage supplied by: |- ! scope="col" style="width:100px;"| Mass flow ! scope="col" style="width:100px;"| Root interception ! scope="col" style="width:100px;"| Diffusion |- | Nitrogen || 98.8 || 1.2 || 0 |- | Phosphorus || 6.3 || 2.8 || 90.9 |- | Potassium || 20.0 || 2.3 || 77.7 |- | Calcium || 71.4 || 28.6 || 0 |- | Sulfur || 95.0 || 5.0 || 0 |- | Molybdenum || 95.2 || 4.8 || 0 |}

In the above table, phosphorus and potassium nutrients move more by diffusion than they do by mass flow in the soil water solution, as they are rapidly taken up by the roots creating a concentration of almost zero near the roots (the plants cannot transpire enough water to draw more of those nutrients near the roots). The very steep concentration gradient is of greater influence in the movement of those ions than is the movement of those by mass flow.<ref>{{cite web |last=Nye |first=Peter H. |url=https://inis.iaea.org/records/5tfnb-a8x79 |title=The diffusion of phosphorus and potassium through soil to a plant root |publisher=IAEA |location=Vienna, Austria |date=September 1966 |access-date=8 May 2026 }}</ref> The movement by mass flow requires the transpiration of water from the plant causing water and solution ions to also move toward the roots.<ref>{{cite journal |last1=Matimati |first1=Ignatious |last2=Verboom |first2=G. Anthony |last3=Cramer |first3=Michael D. |date=January 2014 |title=Nitrogen regulation of transpiration controls mass-flow acquisition of nutrients |journal=Journal of Experimental Botany |volume=65 |issue=1 |pages=159–68 |doi=10.1093/jxb/ert367 |pmid=24231035 |pmc=3883293 |doi-access=free }}</ref> Movement by root interception is slowest, being at the rate plants extend their roots.<ref>{{cite web |url=https://www.agry.purdue.edu/ext/pubs/AGRY-95-08.pdf |title=Roots, growth and nutrient uptake |last=Mengel |first=Dave |publisher=Purdue University, Agronomy Department |location=West Lafayette, Indiana |access-date=8 May 2026 }}</ref>

Plants move ions out of their roots in an effort to move nutrients in from the soil, an exchange process which occurs in the root apoplast.<ref>{{cite journal |last=Sattelmacher |first=Burkhard |date=February 2001 |title=The apoplast and its significance for plant mineral nutrition |journal=New Phytologist |volume=149 |issue=2 |pages=167–92 |doi=10.1046/j.1469-8137.2001.00034.x |pmid=33874640 |url=https://z-library.ec/book/r98J1GpEXD |access-date=8 May 2026 }}</ref> Hydrogen H⁺ is exchanged for other cations, and carbonate (HCO₃⁻) and hydroxide (OH⁻) anions are exchanged for nutrient anions.<ref>{{cite journal |last1=Hinsinger |first1=Philippe |last2=Plassard |first2=Claude |last3=Tang |first3=Caixian |last4=Jaillard |first4=Benoît |date=January 2003 |title=Origins of root-mediated pH changes in the rhizosphere and their responses to environmental constraints: a review |journal=Plant and Soil |volume=248 |issue=1 |pages=43–59 |url=https://www.researchgate.net/publication/226096828 |doi=10.1023/A:1022371130939 |bibcode=2003PlSoi.248...43H |s2cid=23929321 |access-date=8 May 2026 }}</ref> As plant roots remove nutrients from the soil water solution, they are replenished as other ions move off of clay and humus (by ion exchange or desorption), are added from the weathering of soil minerals, and are released by the decomposition of soil organic matter.<ref>{{cite book |last1=Mengel |first1=Konrad |last2=Kirkby |first2=Ernest A. |last3=Kosegarten |first3=Harald |last4=Appel |first4=Thomas |chapter=The soil as a plant nutrient medium |title=Principles of plant nutrition |editor-last1=Mengel |editor-first1=Konrad |editor-last2=Kirkby |editor-first2=Ernest A. |editor-last3=Kosegarten |editor-first3=Harald |editor-last4=Appel |editor-first4=Thomas |year=2001 |publisher=Kluwer Academic Publishers |location=Dordrecht, The Netherlands |chapter-url=https://z-library.ec/book/YypPpaqjyG |isbn=978-94-010-1009-2 |doi=10.1007/978-94-010-1009-2_2 |pages=15–110 |access-date=8 May 2026 }}</ref> However, the rate at which plant roots remove nutrients may not cope with the rate at which they are replenished in the soil solution, stemming in nutrient limitation to plant growth.<ref>{{cite journal |last1=Chapin |first1=F. Stuart III |last2=Vitousek |first2=Peter M. |last3=Van Cleve |first3=Keith |date=January 1986 |title=The nature of nutrient limitation in plant communities |journal=American Naturalist |volume=127 |issue=1 |pages=48–58 |doi=10.1086/284466 |jstor=2461646|s2cid=84381961 |url=https://z-library.ec/book/DLnWz7lM96 |access-date=8 May 2026 }}</ref> Plants derive a large proportion of their anion nutrients from decomposing organic matter, which typically holds 90–95% of the soil nitrogen and sulfur and 20–75% of the soil phosphorus.<ref>{{cite book |last1=Bashir |first1=Owais |last2=Ali |first2=Tahir |last3=Baba |first3=Zahoor Ahmad |last4=Rather |first4=G. H. |last5=Bangroo |first5=S. A. |last6=Mukhtar |first6=Sofi Danish |last7=Naik |first7=Nasir |last8=Mohiuddin |first8=Rehana |last9=Bharati |first9=Varsha |last10=Bhat |first10=Rouf Ahmad |chapter=Soil organic matter and its impact on soil properties and nutrient status |title=Microbiota and biofertilizers, Volume 2, Ecofriendly tools for reclamation of degraded soil environs |editor-last1=Dar |editor-first1=Gowhar Hamid |editor-last2=Bhat |editor-first2=Rouf Ahmad |editor-last3=Mehmood |editor-first3=Mohammad Aneesul |editor-last4=Hakeem |editor-first4=Khalid Rehman |year=2021 |publisher=Springer Cham |location=Cham, Switzerland |chapter-url=https://www.researchgate.net/publication/350554907 |isbn=978-3-030-61010-4 |doi=10.1007/978-3-030-61010-4_7 |pages=129–59 |access-date=8 May 2026 }}</ref> Where crops are produced, the replenishment of nutrients in the soil must usually be augmented by the addition of fertilizer or organic matter.

Because nutrient uptake is an active metabolic process, conditions that inhibit root metabolism may also inhibit nutrient uptake.<ref>{{cite book |last=Alam |first=Syed Manzoor |year=1999 |chapter=Nutrient uptake by plants under stress conditions |title=Handbook of plant and crop stress |edition=2nd |editor-first=Mohammad |editor-last=Pessarakli |publisher=Marcel Dekker |location=New York, New York |pages=285–313 |isbn=978-0824719487 |chapter-url=https://www.academia.edu/3409537 |access-date=8 May 2026 }}</ref> Examples of such conditions include waterlogging or soil compaction resulting in poor soil aeration, excessively high or low soil temperatures, and all above-ground conditions that result in low translocation of sugars to plant roots.<ref>{{cite journal |last=Lichtenthaler |first=Hartmut |date=June 1998 |title=The stress concept in plants: an introduction |journal=Annals of the New York Academy of Sciences |volume=851 |pages=187–98 |doi=10.1111/j.1749-6632.1998.tb08993.x |url=https://z-library.ec/book/eXqkk4JN9K |access-date=8 May 2026 }}</ref>

==Carbon== thumb|Measuring soil respiration in the field using an SRS2000 system. Plants obtain their carbon from atmospheric carbon dioxide through photosynthetic carboxylation, to which must be added the uptake of dissolved carbon from the soil solution<ref>{{cite journal |last1=Rasmussen |first1=Jim |last2=Kuzyakov |first2=Yakov |author-link2=Yakov Kuzyakov |date=July 2009 |title=Carbon isotopes as proof for plant uptake of organic nitrogen: relevance of inorganic carbon uptake |url=https://www.academia.edu/16567630 |journal=Soil Biology and Biochemistry |volume=41 |issue=7 |pages=1586–87 |doi=10.1016/j.soilbio.2009.03.006 |bibcode=2009SBiBi..41.1586R |access-date=8 May 2026 }}</ref> and carbon transfer through mycorrhizal networks.<ref>{{cite journal |last1=Fitter |first1=Alastair H. |last2=Graves |first2=Jonathan D. |last3=Watkins |first3=N. K. |last4=Robinson |first4=David |last5=Scrimgeour |first5=Charlie |date=June 1998 |title=Carbon transfer between plants and its control in networks of arbuscular mycorrhizas |journal=Functional Ecology |volume=12 |issue=3 |pages=406–12 |doi=10.1046/j.1365-2435.1998.00206.x |url=https://z-library.ec/book/aXjpZZOA9Y |bibcode=1998FuEco..12..406F |access-date=8 May 2026 }}</ref> About 45% of a plant's dry mass is carbon; plant residues typically have a carbon to nitrogen ratio (C/N) of between 13:1 and 100:1. As the soil organic material is digested by micro-organisms and saprophagous soil fauna, the C/N decreases as the carbonaceous material is metabolized and carbon dioxide (CO₂) is released as a byproduct which then finds its way out of the soil and into the atmosphere. Nitrogen turnover (mostly involved in protein turnover) is lesser than that of carbon (mostly involved in respiration) in the living, then dead matter of decomposers, which are always richer in nitrogen than plant litter, and so it builds up in the soil.<ref>{{cite journal |last1=Manzoni |first1=Stefano |last2=Trofymow |first2=John A. |last3=Jackson |first3=Robert B. |last4=Porporato |first4=Amilcare |date=February 2010 |title=Stoichiometric controls on carbon, nitrogen, and phosphorus dynamics in decomposing litter |journal=Ecological Monographs |volume=80 |issue=1 |pages=89–106 |url=https://jacksonlab.stanford.edu/sites/g/files/sbiybj20871/files/media/file/em10.pdf |doi=10.1890/09-0179.1 |bibcode=2010EcoM...80...89M |access-date=8 May 2026 }}</ref> Normal CO₂ concentration in the atmosphere is 0.03%, this can be the factor limiting plant growth when no other factor like water or nutrient scarcity is involved.<ref>{{cite journal |last1=Boretti |first1=Albert |last2=Florentine |first2=Singarayer |date=4 April 2019 |title=Atmospheric CO2 concentration and other limiting factors in the growth of C3 and C4 plants |journal=Plants |volume=8 |issue=4 |article-number=92 |doi=10.3390/plants8040092 |doi-access=free |pmc=6524366 }}</ref> The respiration of CO₂ by soil microorganisms decomposing soil organic matter and the CO₂ respired by roots contribute an important amount of CO₂ to the photosynthesising plants, to which must be added the CO₂ respired by aboveground plant tissues.<ref>{{cite journal |last1=Teskey |first1=Robert O. |last2=Saveyn |first2=An |last3=Steppe |first3=Kathy |last4=McGuire |first4=Mary Ann |year=2007 |title=Origin, fate and significance of CO2 in tree stems |journal=New Phytologist |volume=177 |issue=1 |pages=17–32 |doi=10.1111/j.1469-8137.2007.02286.x |pmid=18028298 |url=https://z-library.ec/book/YyVzDKmwyp |access-date=11 May 2026 }}</ref> Root-respired CO₂ can be accumulated overnight within hollow stems of plants, to be further used for photosynthesis during the day.<ref>{{cite journal |last1=Billings |first1=William Dwight |last2=Godfrey |first2=Paul Joseph |year=1967 |title=Photosynthetic utilization of internal carbon dioxide by hollow-stemmed plants |journal=Science |volume=158 |issue=3797 |pages=121–23 |doi=10.1126/science.158.3797.121 |pmid=6054809 |jstor=1722393|bibcode=1967Sci...158..121B |s2cid=13237417 |url=https://fr.zlib-articles.se/book/22613832/23b161 |access-date=5 November 2023 }}</ref> Within the soil, CO₂ concentration is 10 to 100 times that of atmospheric levels<ref>{{cite journal |last1=Brook |first1=George A. |last2=Folkoff |first2=Michael E. |last3=Box |first3=Elgene O. |date=January–February 1983 |title=A world model of soil carbon dioxide |journal=Earth Surface Processes and Landforms |volume=8 |issue=1 |pages=79–88 |doi=10.1002/esp.3290080108 |url=https://z-library.ec/book/Z9knRQraLO |access-date=11 May 2026 }}</ref> but may rise to toxic levels if the soil porosity is low or if diffusion is impeded by flooding.<ref>{{cite journal |last=Kozlowski |first=Theodore Thomas |date=March 1985 |title=Soil aeration, flooding, and tree growth |journal=Arboriculture & Urban Forestry |volume=11 |issue=3 |pages=85–95 |doi=10.48044/jauf.1985.022 |doi-access=free }}</ref>

==Nitrogen== {{Further|Nitrogen cycle}} thumb|upright=0.9|{{center|Generalization of percent soil nitrogen by soil order}} Nitrogen is the most critical element obtained by plants from the soil, to the exception of moist tropical forests (tropical rainforests) where phosphorus is the limiting soil nutrient,<ref>{{cite journal |last=Vitousek |first=Peter M. |year=1984 |title=Litterfall, nutrient cycling, and nutrient limitation in tropical forests |journal=Ecology |volume=65 |issue=1 |pages=285–98 |url=https://www.academia.edu/7519799 |doi=10.2307/1939481 |access-date=12 May 2026 |jstor=1939481 |bibcode=1984Ecol...65..285V }}</ref> and nitrogen deficiency often limits plant growth through decreased photosynthetic rate.<ref>{{cite journal |last1=Mu |first1=Xiaohuan |last2=Chen |first2=Yanling |date=January 2021 |title=The physiological response of photosynthesis to nitrogen deficiency |journal=Plant Physiology and Biochemistry |volume=158 |pages=76–82 |doi=10.1016/j.plaphy.2020.11.019 |url=https://z-library.ec/book/09Q51EKE9p |access-date=12 May 2026 }}</ref> Plants can use nitrogen as either the ammonium cation (NH₄⁺) or the anion nitrate (NO₃⁻). Plants are commonly classified as ammonium or nitrate plants according to their preferential nitrogen nutrition.<ref>{{cite journal |last1=Forde |first1=Bryan G. |last2=Clarkson |first2=David T. |year=1999 |title=Nitrate and ammonium nutrition of plants: physiological and molecular perspectives |journal=Advances in Botanical Research |volume=30 |issue=C |pages=1–90 |url=https://www.researchgate.net/publication/223786872 |doi=10.1016/S0065-2296(08)60226-8 |access-date=12 May 2026 }}</ref> Usually, most of the nitrogen in soil is bound within organic compounds that make up the soil organic matter, and must be mineralized to the ammonium or nitrate form before it can be taken up by most plants.<ref>{{cite journal |last1=Xu |first1=Guohua |last2=Fan |first2=Xiaorong |last3=Miller |first3=Anthony J. |date=June 2012 |title=Plant nitrogen assimilation and use efficiency |journal=Annual Review of Plant Biology |volume=63 |pages=153–82 |doi=10.1146/annurev-arplant-042811-105532 |url=https://www.researchgate.net/publication/221728687 |access-date=12 May 2026 }}</ref> However, symbiosis with mycorrhizal fungi allow plants to get access to the organic nitrogen pool where and when mineral forms of nitrogen are poorly available.<ref>{{cite journal |last1=Hodge |first1=Angela |last2=Campbell |first2=Colin D. |last3=Fitter |first3=Alastair H. |year=2001 |title=An arbuscular mycorrhizal fungus accelerates decomposition and acquires nitrogen directly from organic material |journal=Nature |volume=413 |issue=6853 |pages=297–99 |url=https://eprints.whiterose.ac.uk/id/eprint/141/1/hodgea1.pdf |doi=10.1038/35095041 |pmid=11565029 |access-date=12 May 2026 |bibcode=2001Natur.413..297H |s2cid=4423745 }}</ref> The total nitrogen content depends largely on the soil organic matter content, which in turn depends on texture, climate, vegetation, topography, age and soil management.<ref>{{cite journal |last1=Burke |first1=Ingrid C. |author-link1=Ingrid Burke |last2=Yonker |first2=Caroline M. |last3=Parton |first3=William J. |last4=Cole |first4=C. Vernon |last5=Flach |first5=Klaus |last6=Schimel |first6=David S. |date=May–June 1989 |title=Texture, climate, and cultivation effects on soil organic matter content in U.S. grassland soils |journal=Soil Science Society of America Journal |volume=53 |issue=3 |pages=800–05 |url=https://www.researchgate.net/publication/233209856 |doi=10.2136/sssaj1989.03615995005300030029x |access-date=12 May 2026 |bibcode=1989SSASJ..53..800B }}</ref> Soil nitrogen typically decreases by 0.2 to 0.3% for every temperature increase by 10&nbsp;°C.<ref>{{cite journal |last=Jenny |first=Hans |date=March 1929 |title=Relation of temperature to the amount of nitrogen in soils |journal=Soil Science |volume=27 |issue=3 |pages=169–88 |url=https://z-library.ec/book/PXzYOgNRy6 |doi=10.1097/00010694-192903000-00001 |access-date=12 May 2026 }}</ref> Usually, grassland soils contain more soil nitrogen than forest soils, because of a higher turnover rate of grassland organic matter.<ref>{{cite journal |last1=Enríquez |first1=Susana |last2=Duarte |first2=Carlos M. |last3=Sand-Jensen |first3=Kaj |date=July 1993 |title=Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C:N:P content |journal=Oecologia |volume=94 |issue=4 |pages=457–71 |url=https://www.researchgate.net/publication/227157788 |doi=10.1007/BF00566960 |pmid=28313985 |access-date=12 May 2026 |bibcode=1993Oecol..94..457E |s2cid=22732277 }}</ref> Cultivation decreases soil nitrogen by exposing soil organic matter to decomposition by microorganisms,<ref>{{cite journal |last1=Tiessen |first1=Holm |last2=Stewart |first2=John W. B. |last3=Bettany |first3=Jeff R. |year=1982 |title=Cultivation effects on the amounts and concentration of carbon, nitrogen, and phosphorus in grassland soils |journal=Agronomy Journal |volume=74 |issue=5 |pages=831–35 |url=https://z-library.ec/book/WyreKRm39J |doi=10.2134/agronj1982.00021962007400050015x |bibcode=1982AgrJ...74..831T |access-date=12 May 2026 }}</ref> most losses being caused by denitrification,<ref>{{cite book |last1=Philippot |first1=Laurent |last2=Hallin |first2=Sara |last3=Schloter |first3=Michael |year=2007 |chapter=Ecology of denitrifying prokaryotes in agricultural soil |title=Advances in Agronomy |volume=96 |pages=249–305 |editor-last=Sparks |editor-first=Donald L. |publisher=Elsevier |location=Amsterdam, the Netherlands |isbn=978-0-12-374206-3 |citeseerx=10.1.1.663.4557 |chapter-url=https://www.academia.edu/96597816 |access-date=12 May 2026 }}</ref> and soils under no-tillage maintain more soil nitrogen than tilled soils.<ref>{{cite journal |last=Doran |first=John W. |year=1987 |title=Microbial biomass and mineralizable nitrogen distributions in no-tillage and plowed soils |journal=Biology and Fertility of Soils |volume=5 |issue=1 |pages=68–75 |url=https://z-library.ec/book/Jy1pPRgB9z |doi=10.1007/BF00264349 |bibcode=1987BioFS...5...68D |s2cid=44201431 |access-date=12 May 2026 }}</ref>

Some micro-organisms are able to metabolise organic matter and release ammonium in a process called mineralisation. Others, called nitrifiers, take free ammonium or nitrite as an intermediary step in the process of nitrification, and oxidise it to nitrate. Nitrogen-fixing bacteria are capable of metabolising N₂ into the form of ammonia or related nitrogenous compounds in a process called nitrogen fixation. Both ammonium and nitrate can be immobilized by their incorporation into microbial living cells, where it is temporarily sequestered in the form of amino acids and proteins.<ref>{{cite book |last1=Myrold |first1=David D. |last2=Bottomley |first2=Peter J. |date=15 June 2008 |chapter=Nitrogen mineralization and immobilization |title=Nitrogen in agricultural systems |volume=49 |pages=157–72 |editor-last1=Schepers |editor-first1=James S. |editor-last2=Raun |editor-first2=William R. |publisher=American Society of Agronomy |location=Madison, Wisconsin |isbn=9780891181910 |doi=10.2134/agronmonogr49.c5 |chapter-url=https://z-library.ec/book/Yypmp2W8XG |access-date=12 May 2026 }}</ref> Nitrate may be lost from the soil to the atmosphere when bacteria metabolise it to the gases NH₃, N₂ and N₂O, a process called denitrification. Nitrogen may also be leached from the vadose zone if in the form of nitrate, acting as a pollutant if it reaches the water table or flows over land, more especially in agricultural soils under high use of nutrient fertilizers.<ref>{{cite journal |last1=Mahvi |first1=Amir H. |last2=Nouri |first2=Jafar |last3=Babaei |first3=Ali A. |last4=Nabizadeh |first4=Ramin |year=2005 |title=Agricultural activities impact on groundwater nitrate pollution |journal=International Journal of Environmental Science and Technology |volume=2 |issue=1 |pages=41–47 |url=https://www.researchgate.net/publication/43562804 |doi=10.1007/BF03325856 |bibcode=2005JEST....2...41M |s2cid=94640003 |access-date=12 May 2026 |hdl=1807/9114 |hdl-access=free }}</ref> Ammonium may also be sequestered in 2:1 clay minerals.<ref>{{cite journal |last1=Scherer |first1=Heinrich W. |last2=Feils |first2=E. |last3=Beuters |first3=Patrick |date=31 July 2014 |title=Ammonium fixation and release by clay minerals as influenced by potassium |journal=Plant, Soil and Environment |volume=60 |issue=7 |pages=325–31 |doi=10.17221/202/2014-PSE |s2cid=55200516 |doi-access=free }}</ref> A small amount of nitrogen is added to soil by rainfall, to the exception of wide areas of North America and West Europe where the excess use of nitrogen fertilizers and manure has caused atmospheric pollution by ammonia emission, stemming in soil acidification and eutrophication of soils and aquatic ecosystems.<ref>{{cite journal |last1=Barak |first1=Phillip |last2=Jobe |first2=Babou O. |last3=Krueger |first3=Armand R. |last4=Peterson |first4=Lloyd A. |last5=Laird |first5=David A. |date=November 1997 |title=Effects of long-term soil acidification due to nitrogen fertilizer inputs in Wisconsin |journal=Plant and Soil |volume=197 |issue=1 |pages=61–69 |url=https://www.academia.edu/15240998 |doi=10.1023/A:1004297607070 |bibcode=1997PlSoi.197...61B |s2cid=2410167 |access-date=12 May 2026 }}</ref><ref>{{cite journal |last1=Van Egmond |first1=Klaas |last2=Bresser |first2=Ton |last3=Bouwman |first3=Lex |date=March 2002 |title=The European nitrogen case |journal=Ambio |volume=31 |issue=2 |pages=72–78 |url=https://www.klaasvanegmond.nl/wp-content/uploads/2017/05/European-Nitrogen-case.pdf |doi=10.1579/0044-7447-31.2.72 |pmid=12078012 |bibcode=2002Ambio..31...72V |s2cid=1114679 |access-date=12 May 2026 }}</ref><ref name="Roy2006"/>

===Gains===

In the process of mineralisation, microbes feed on organic matter, releasing ammonia (NH₃), ammonium (NH₄⁺), nitrate (NO₃⁻) and other nutrients. As long as the carbon to nitrogen ratio (C/N) of fresh residues in the soil is above 30:1, nitrogen will be in short supply for the nitrogen-rich microbal biomass (nitrogen deficiency), and other bacteria will uptake ammonium and to a lesser extent nitrate and incorporate them into their cells in the immobilization process.<ref>{{cite journal |last1=Recous |first1=Sylvie |last2=Mary |first2=Bruno |year=1990 |title=Microbial immobilization of ammonium and nitrate in cultivated soils |journal=Soil Biology and Biochemistry |volume=22 |issue=7 |pages=913–22 |url=https://www.academia.edu/20027179 |doi=10.1016/0038-0717(90)90129-N |bibcode=1990SBiBi..22..913R |access-date=12 May 2026 }}</ref> In that form the nitrogen is said to be ''immobilised''. Later, when such bacteria die and decay, they too are ''mineralised'' and some of the nitrogen is released as ammonium and nitrate.<ref>{{cite journal |last=Mengel |first=Konrad |date=April 1996 |title=Turnover of organic nitrogen in soils and its availability to crops |journal=Plant and Soil |volume=181 |pages=83–93 |url=https://z-library.ec/book/4LYo5NB3y2 |doi=10.1007/BF00011295 |access-date=12 May 2026 }}</ref> Predation of bacteria by soil fauna, in particular protozoa and nematodes, play a decisive role in the return of immobilized nitrogen to mineral forms.<ref>{{cite journal |last1=Verhoef |first1=Herman A. |last2=Brussaard |first2=Lijbert |date=December 1990 |title=Decomposition and nitrogen mineralization in natural and agro-ecosystems: the contribution of soil animals |journal=Biogeochemistry |volume=11 |issue=3 |pages=175–211 |url=https://www.researchgate.net/publication/226533290 |doi=10.1007/BF00004496 |bibcode=1990Biogc..11..175V |s2cid=96922131 |access-date=12 May 2026 }}</ref> If the C/N of fresh residues is less than 15, mineral nitrogen is freed to the soil and directly available to plants.<ref>{{cite journal |last1=Chen |first1=Baoqing |last2=Liu |first2=EnKe |last3=Tian |first3=Qizhuo |last4=Yan |first4=Changrong |last5=Zhang |first5=Yanqing |date=28 February 2014 |title=Soil nitrogen dynamics and crop residues: a review |journal=Agronomy for Sustainable Development |volume=34 |issue=2 |pages=429–42 |url=https://hal.archives-ouvertes.fr/hal-01234828/document |doi=10.1007/s13593-014-0207-8 |s2cid=18024074 |access-date=12 May 2026 }}</ref> Bacteria may on average add 50&nbsp;kg nitrogen per hectare (net mineralization rate), and in an unfertilised field this is the most important source of usable nitrogen, corresponding roughly to 2% total soil nitrogen.<ref>{{cite journal |last1=Stenger |first1=Roland |last2=Priesack |first2=Eckart |last3=Beese |first3=Friedrich |date=April 1995 |title=Rates of net nitrogen mineralization in disturbed and undisturbed soils |journal=Plant and Soil |volume=171 |pages=323–32 |url=https://www.academia.edu/115811709 |doi=10.1007/BF00010288 |access-date=12 May 2026 }}</ref> It occurs fastest in warm, moist, well aerated soil.<ref>{{cite journal |last1=Griffin |first1=Timothy S. |last2=Honeycutt |first2=Charles W. |last3=He |first3=Zhijun |date=December 2002 |title=Effects of temperature, soil water status, and soil type on swine slurry nitrogen transformations |journal=Biology and Fertility of Soils |volume=36 |issue=6 |pages=442–46 |url=https://www.academia.edu/33923015 |doi=10.1007/s00374-002-0557-2 |bibcode=2002BioFS..36..442T |s2cid=19377528 |access-date=13 May 2026 }}</ref>

{| class="wikitable sortable floatright" |+ Carbon/Nitrogen Ratio of Various Organic Materials<ref>{{cite book |url=https://archive.org/details/soilsintroductio00dona/page/144/mode/2up |title=Soils: an introduction to soils and plant growth |edition=4th |last1=Donahue |first1=Roy Luther |last2=Miller |first2=Raymond W. |last3=Shickluna |first3=John C. |publisher=Prentice-Hall |location=Englewood Cliffs, New Jersey |year=1977 |isbn=978-0138219185 |page=145 |access-date=13 May 2026 }}</ref> |- ! scope="col" | Organic Material ! scope="col" | C:N Ratio |- | Alfalfa || 13 |- | Bacteria || 4 |- | Clover, green sweet || 16 |- | Clover, mature sweet || 23 |- | Fungi || 9 |- | Forest litter || 30 |- | Humus in warm cultivated soils || 11 |- | Legume-grass hay || 25 |- | Legumes (alfalfa or clover), mature || 20 |- | Manure, cow || 18 |- | Manure, horse || 16–45 |- | Manure, human || 10 |- | Oat straw || 80 |- | Straw, cornstalks || 90 |- | Sawdust || 250 |}

In nitrogen fixation, rhizobium bacteria convert N₂ to ammonia (NH₃), which is rapidly converted to amino acids, parts of which are used by the rhizobia for the synthesis of their own biomass proteins, while other parts are transported to the xylem of the host plant.<ref>{{cite journal |last1=Lodwig |first1=Emma |last2=Hosie |first2=Arthur H. F. |last3=Bourdès |first3=Alexandre |last4=Findlay |first4=Kim |last5=Allaway |first5=David |last6=Karunakaran |first6=Ramakrishnan |last7=Downie |first7=J. Allan |last8=Poole |first8=Philip S. |year=2003 |title=Amino-acid cycling drives nitrogen fixation in the legume–Rhizobium symbiosis |journal=Nature |volume=422 |issue=6933 |pages=722–6 |url=https://www.researchgate.net/publication/10799601 |doi=10.1038/nature01527 |pmid=12700763 |bibcode=2003Natur.422..722L |s2cid=4429613 |access-date=13 May 2026 }}</ref> Rhizobia share a symbiotic relationship with host plants, since rhizobia supply the host with nitrogen and the host provides rhizobia with other nutrients and a safe environment. It is estimated that such symbiotic bacteria in the root nodules of legumes add potentially 200 to 300 kilograms of nitrogen per hectare per year, which may be sufficient for the crop.<ref>{{cite journal |last1=Peoples |first1=Matt B. |last2=Herridge |first2=David F. |last3=Ladha |first3=Jagdish K. |date=July 1995 |title=Biological nitrogen fixation: an efficient source of nitrogen for sustainable agricultural production? |journal=Plant and Soil |volume=174 |pages=3–28 |url=https://www.academia.edu/23113142 |doi=10.1007/BF00032239 |access-date=13 May 2026 }}</ref> Other, free-living nitrogen-fixing diazotroph bacteria and archaea live independently in the soil and release mineral forms of nitrogen when their dead bodies are converted by way of mineralization, free-living nitrogen fixation being the dominant source of N availability in temperate forests, temperate grasslands, and shrublands.<ref>{{cite journal |last1=Khan |first1=Sehroon |last2=Nadir |first2=Sadia |last3=Iqbal |first3=Shahid |last4=Xu |first4=Jianshu |last5=Gui |first5=Heng |last6=Khan |first6=Afsar |last7=Ye |first7=Lei |date=30 November 2021 |title=Towards a comprehensive understanding of free-living nitrogen fixation |journal=Circular Agricultural Systems |volume=1 |article-number=13 |doi=10.48130/CAS-2021-0013 |doi-access=free }}</ref>

Some amount of atmospheric nitrogen is transformed by lightnings in gaseous nitric oxide (NO) and nitrogen dioxide (NO₂⁻).<ref>{{cite journal |last1=Hill |first1=Robert D. |last2=Rinker |first2=Robert G. |last3=Wilson |first3=H. Dale |year=1980 |title=Atmospheric nitrogen fixation by lightning |journal=Journal of the Atmospheric Sciences |volume=37 |issue=1 |pages=179–92 |doi=10.1175/1520-0469(1980)037<0179:ANFBL>2.0.CO;2 |bibcode=1980JAtS...37..179H |url=https://z-library.ec/book/PXzb2xQRX6 |access-date=14 May 2026 }}</ref> Nitrogen dioxide is soluble in water to form nitric acid (HNO₃) dissociating in H⁺ and NO₃⁻.<ref>{{cite journal |last1=Lee |first1=Y. N. |last2=Schwartz |first2=Stephen E. |date=April 1981 |title=Reaction kinetics of nitrogen dioxide with liquid water at low partial pressure |journal=The Journal of Physical Chemistry |volume=85 |issue=7 |pages=840–8 |doi=10.1021/j150607a022 |url=https://z-library.ec/book/gyxlxRdnyo |access-date=14 May 2026 }}</ref> Ammonia, NH₃, previously emitted from the soil, may fall with precipitation up to a rate of about 40 and 50&nbsp;kg ha−1 yr−1 then be taken up by vegetation foliage and roots, fixed in the soil by clay minerals and humus or transformed by nitrification as nitric acid, becoming a prominent agent of soil acidification.<ref>{{cite journal |last1=Pearson |first1=John |last2=Stewart |first2=George R. |date=October 1993 |title=The deposition of atmospheric ammonia and its effects on plants |journal=New Phytologist |volume=125 |issue=2 |pages=225–431 |doi=10.1111/j.1469-8137.1993.tb03882.x |url=https://z-library.ec/book/5X0J5VG29r |access-date=14 May 2026 }}</ref>

===Sequestration===

When bacteria feed on soluble forms of nitrogen (ammonium and nitrate), they temporarily sequester that nitrogen in their bodies in a process called immobilization. At a later time when those bacteria die, their nitrogen may be released as ammonium by the process of mineralization, sped up by predatory fauna.<ref>{{cite journal |last1=Ferris |first1=Howard |last2=Venette |first2=Robert C. |last3=Van der Meulen |first3=Hans R. |last4=Lau |first4=Serrine S. |date=June 1998 |title=Nitrogen mineralization by bacterial-feeding nematodes: verification and measurement |journal=Plant and Soil |volume=203 |issue=2 |pages=159–71 |url=https://www.academia.edu/13798247 |doi=10.1023/A:1004318318307 |bibcode=1998PlSoi.203..159F |s2cid=20632698 |access-date=14 May 2026 }}</ref>

Protein material is easily broken down, but the rate of its decomposition is slowed by its attachment to the crystalline structure of clay and when trapped between the clay layers<ref>{{cite journal |last1=Violante |first1=Antonio |last2=de Cristofaro |first2=Annunziata |last3=Rao |first3=Maria A. |last4=Gianfreda |first4=Liliana |date=December 1995 |title=Physicochemical properties of protein-smectite and protein-Al(OH)x-smectite complexes |journal=Clay Minerals |volume=30 |issue=4 |pages=325–36 |url=https://www.researchgate.net/publication/249852957 |doi=10.1180/claymin.1995.030.4.06 |bibcode=1995ClMin..30..325V |s2cid=94630893 |access-date=14 May 2026 }}</ref> or attached to rough clay surfaces.<ref>{{cite journal |last1=Vogel |first1=Cordula |last2=Mueller |first2=Carsten W. |last3=Höschen |first3=Carmen |last4=Buegger |first4=Franz |last5=Heister |first5=Katja |last6=Schulz |first6=Stefanie |last7=Schloter |first7=Michael |last8=Kögel-Knabner |first8=Ingrid|author8-link=Ingrid Kögel-Knabner |year=2014 |title=Submicron structures provide preferential spots for carbon and nitrogen sequestration in soils |journal=Nature Communications |volume=5 |issue=2947 |pages=1–7 |doi=10.1038/ncomms3947 |pmid=24399306 |pmc=3896754|bibcode=2014NatCo...5.2947V |doi-access=free }}</ref> The layers are small enough that bacteria cannot enter.<ref>{{cite journal |last1=Ruamps |first1=Léo Simon |last2=Nunan |first2=Naoise |last3=Chenu |first3=Claire |date=February 2011 |title=Microbial biogeography at the soil pore scale |journal=Soil Biology and Biochemistry |volume=43 |issue=2 |pages=280–6 |url=https://www.academia.edu/23734881 |doi=10.1016/j.soilbio.2010.10.010 |bibcode=2011SBiBi..43..280R |access-date=14 May 2026 }}</ref> Some organisms exude extracellular enzymes that can act on the sequestered proteins. However, those enzymes too may be trapped on the clay crystals, resulting in a complex interaction between proteins, microbial enzymes and mineral surfaces.<ref>{{cite journal |last1=Quiquampoix |first1=Hervé |last2=Burns |first2=Richard G. |date=December 2007 |title=Interactions between proteins and soil mineral surfaces: environmental and health consequences |journal=Elements |volume=3 |issue=6 |pages=401–6 |url=https://www.academia.edu/6441123 |doi=10.2113/GSELEMENTS.3.6.401 |bibcode=2007Eleme...3..401Q |access-date=14 May 2026 }}</ref>

Ammonium fixation occurs mainly between the layers of 2:1 type clay minerals such as illite, vermiculite or montmorillonite, together with ions of similar ionic radius and low hydration energy such as potassium, but a small proportion of ammonium is also fixed in the silt fraction.<ref>{{cite journal |last1=Nieder |first1=Rolf |last2=Benbi |first2=Dinesh K. |last3=Scherer |first3=Heinrich W. |year=2011 |title=Fixation and defixation of ammonium in soils: a review |journal=Biology and Fertility of Soils |volume=47 |issue=1 |pages=1–14 |doi=10.1007/s00374-010-0506-4 |s2cid=7284269 |doi-access=free |bibcode=2011BioFS..47....1N }}</ref>

===Losses===

Usable nitrogen may be lost from soils when it is in the form of nitrate, as it is easily leached, contrary to ammonium which is easily fixed.<ref name="Kramer2006">{{cite journal |last1=Kramer |first1=Sasha B. |last2=Reganold |first2=John P. |last3=Glover |first3=Jerry D. |last4=Bohannan |first4=Brendan J.M. |author-link4=Brendan Bohannan |last5=Mooney |first5= Harold A. |date=13 March 2006 |title=Reduced nitrate leaching and enhanced denitrifier activity and efficiency in organically fertilized soils |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=103 |issue=12 |pages=4522–7 |doi=10.1073/pnas.0600359103 |pmid=16537377 |pmc=1450204|bibcode=2006PNAS..103.4522K |doi-access=free }}</ref> Further losses of nitrogen occur by denitrification, the process whereby soil bacteria convert nitrate (NO₃⁻) to nitrogen gas, N₂ or N₂O. This occurs when poor soil aeration limits free oxygen, forcing bacteria to use the oxygen in nitrate for their respiratory process.<ref>{{cite journal |last1=Scott Smith |first1=M. |last2=Tiedje |first2=James M. |year=1979 |title=Phases of denitrification following oxygen depletion in soil |journal=Soil Biology and Biochemistry |volume=11 |issue=3 |pages=261–7 |url=https://z-library.ec/book/PLKrdYrmXB |doi=10.1016/0038-0717(79)90071-3 |access-date=14 May 2026 }}</ref> Denitrification increases when oxidisable organic material is available, as in organic farming<ref name="Kramer2006"/> and when soils are warm and slightly acidic, as currently happens in tropical areas.<ref>{{cite book |last=Robertson |first=G. Philip |year=1989 |chapter=Nitrification and denitrification in humid tropical ecosystems: potential controls on nitrogen retention |title=Mineral nutrients in tropical forest and savanna ecosystems |chapter-url=https://lter.kbs.msu.edu/docs/robertson/robertson+1989+mineral+nutrients.pdf |editor-last=Proctor |editor-first=John |publisher=Blackwell Scientific |location=Cambridge, Massachusetts |isbn=978-0632025596 |access-date=14 May 2026 }}</ref> Denitrification may vary throughout a soil as the aeration varies from place to place.<ref>{{cite journal |last1=Parkin |first1=Timothy B. |last2=Robinson |first2=Joseph A. |date=January 1989 |title=Stochastic models of soil denitrification |journal=Applied and Environmental Microbiology |volume=55 |issue=1 |pages=72–7 |pmid=16347838 |pmc=184056 |doi=10.1128/AEM.55.1.72-77.1989 |doi-access=free |bibcode=1989ApEnM..55...72P }}</ref> Denitrification may cause the loss of 25&nbsp;percent of the N applied on a heavy clay soil as fertilizer and manure.<ref>{{cite journal |last1=Van der Salm |first1=Caroline |last2=Dolfing |first2=Jan |last3=Heinen |first3=Marius |last4=Velthof |first4=Gerard L. |date=March 2007 |title=Estimation of nitrogen losses via denitrification from a heavy clay soil under grass |journal=Agriculture, Ecosystems & Environment |volume=119 |issue=3–4 |pages=311–9 |url=https://www.academia.edu/16633686 |doi=10.1016/j.agee.2006.07.018 |access-date=14 May 2026 }}</ref>

Ammonia volatilisation occurs when ammonium reacts chemically with an alkaline soil, converting NH₄⁺ to NH₃.<ref>{{cite journal |last1=Rao |first1=Desiraju L.N. |last2=Batra |first2=Lalit |date=June 1983 |title=Ammonia volatilization from applied nitrogen in alkali soils |journal=Plant and Soil |volume=70 |issue=2 |pages=219–28 |url=https://www.researchgate.net/publication/226710175 |doi=10.1007/BF02374782 |bibcode=1983PlSoi..70..219R |s2cid=24724207 |access-date=14 May 2026 }}</ref> The application of ammonium fertiliser to such a field can result in volatilisation losses of as much as 87 percent.<ref>{{cite journal |last=Jewitt |first=T. N. |date=December 1942 |title=Loss of ammonia from ammonium sulfate applied to alkaline soils |journal=Soil Science |volume=54 |issue=6 |pages=401–10 |url=https://z-library.ec/book/5X0dq1grXr |doi=10.1097/00010694-194212000-00002 |access-date=14 May 2026 }}</ref>

All kinds of nitrogen losses, whether by leaching or volatilization, are responsible for a large part of aquifer pollution<ref>{{cite journal |last1=Lallouette |first1=Vincent |last2=Magnier |first2=Julie |last3=Petit |first3=Katell |last4=Michon |first4=Janik |date=December 2014 |title=Agricultural practices and nitrates in aquatic environments |journal=The Brief |volume=11 |issue=December |pages=1–16 |url=https://www.oieau.fr/eaudoc/system/files/nitrates_20102011_201412_EN.pdf |access-date=14 May 2026 }}</ref> and air pollution, with concomitant effects on soil acidification and eutrophication,<ref>{{cite journal |last1=Choudhury |first1=Abu T. M. A. |last2=Kennedy |first2=Ivan R. |year=2005 |title=Nitrogen fertilizer losses from rice soils and control of environmental pollution problems |journal=Communications in Soil Science and Plant Analysis |volume=36 |issue=11–12 |pages=1625–39 |url=https://www.researchgate.net/publication/249074007 |access-date=14 May 2026 |doi=10.1081/css-200059104 |bibcode=2005CSSPA..36.1625C |s2cid=44014545 }}</ref> a novel combination of environmental threats (acidity and excess nitrogen) to which extant organisms are badly adapted, causing severe biodiversity losses in natural ecosystems.<ref>{{cite journal |last1=Roth |first1=Tobias |last2=Kohli |first2=Lukas |last3=Rihm |first3=Beat |last4=Achermann |first4=Beat |date=15 September 2013 |title=Nitrogen deposition is negatively related to species richness and species composition of vascular plants and bryophytes in Swiss mountain grassland |journal=Agriculture, Ecosystems and Environment |volume=178 |pages=121–26 |url=https://z-library.ec/book/8L77gQwxL0 |access-date=14 May 2026 |doi=10.1016/j.agee.2013.07.002 |bibcode=2013AgEE..178..121R }}</ref>

==Phosphorus==

After nitrogen, phosphorus is probably the element most likely to be deficient in soils, although it often turns to be the most deficient in tropical soils where the mineral pool is depleted under intense leaching and mineral weathering while, contrary to nitrogen, phosphorus reserves cannot be replenished from atmospheric sources.<ref>{{cite journal |last=Vitousek |first=Peter M. |date=February 1984 |title=Litterfall, nutrient cycling, and nutrient limitation in tropical forests |journal=Ecology |volume=65 |issue=1 |pages=285–98 |url=https://www.academia.edu/7519799 |doi=10.2307/1939481 |access-date=14 May 2026 |jstor=1939481 |bibcode=1984Ecol...65..285V }}</ref> The soil mineral apatite is the most common mineral source of phosphorus, from which it can be extracted by microbial and root exudates,<ref>{{cite journal |last=Kucey |first=Reg M.N. |date=November 1983 |title=Phosphate-solubilizing bacteria and fungi in various cultivated and virgin Alberta soils |journal=Canadian Journal of Soil Science |volume=63 |issue=4 |pages=671–8 |doi=10.4141/cjss83-068 |doi-access=free }}</ref><ref>{{cite journal |last1=Khorassani |first1=Reza |last2=Hettwer |first2=Ursula |last3=Ratzinger |first3=Astrid |last4=Steingrobe |first4=Bernd |last5=Karlovsky |first5=Petr |last6=Claassen |first6=Norbert |date=26 August 2011 |title=Citramalic acid and salicylic acid in sugar beet root exudates solubilize soil phosphorus |journal=BMC Plant Biology |volume=11 |issue=121 |pages=1–8 |doi=10.1186/1471-2229-11-121 |pmid=21871058 |pmc=3176199 |doi-access=free }}</ref> with an important contribution of arbuscular mycorrhizal fungi.<ref>{{cite journal |last1=Duponnois |first1=Robin |last2= Colombet |first2=Aline |last3=Hien |first3=Victor |last4=Thioulouse |first4=Jean |date=August 2005 |title=The mycorrhizal fungus ''Glomus intraradices'' and rock phosphate amendment influence plant growth and microbial activity in the rhizosphere of ''Acacia holosericea'' |journal=Soil Biology and Biochemistry |volume=37 |issue=8 |pages=1460–8 |url=https://pbil.univ-lyon1.fr/JTHome/ref/Dupo2005a.pdf |doi=10.1016/j.soilbio.2004.09.016 |bibcode=2005SBiBi..37.1460D |access-date=14 May 2026 }}</ref> The most common form of organic phosphate is phytate, the principal storage form of phosphorus in many plant tissues.<ref>{{cite journal |last1=Alkarawi |first1=Hassan Hadi |last2=Zotz |first2=Gerhard |date=July 2014 |title=Phytic acid in green leaves |journal=Plant Biology |volume=16 |issue=4 |pages=697–701 |doi=10.1111/plb.12136 |url=https://www.academia.edu/14467730 |access-date=14 May 2026 }}</ref> In the soil, phosphorus is generally in the form of orthophosphate with low solubility, except when linked to ammonium or calcium, hence the use of diammonium phosphate or monocalcium phosphate as fertilizers.<ref>{{cite book |last1=Syers |first1=John Keith |last2=Johnston |first2=A. Edward |last3=Curtin |first3=Denis |date=2008 |title=Efficiency of soil and fertilizer phosphorus use: reconciling changing concepts of soil phosphorus behaviour with agronomic information |publisher=Food and Agriculture Organization of the United Nations |location=Rome, Italy |isbn=978-92-5-105929-6 |url=https://openknowledge.fao.org/server/api/core/bitstreams/01a2006a-bb36-436a-a027-acead43dc013/content |access-date=14 May 2026 }}</ref> Total phosphorus is in average 0.06&nbsp;percent by weight of the soil, but may vary by up to three orders of magnitude across the globe,<ref>{{cite journal |last1=He |first1=Xianjin |last2=Augusto |first2=Laurent |last3=Goll |first3=Daniel S. |last4=Ringeval |first4=Bruno |last5=Wang |first5=Yingping |last6=Helfenstein |first6=Julian |last7=Huang |first7=Yuanyuan |last8=Yu |first8=Kailiang |last9=Wang |first9=Zhiqiang |last10=Yang |first10=Yongchuan |last11=Hou |first11=Enqing |date=20 December 2021 |title=Global patterns and drivers of soil total phosphorus concentration |journal=Earth System Science Data |volume=13 |pages=5831–46 |doi=10.6084/m9.figshare.14583375 |doi-access=free }}</ref> and is mainly in organic form, not directly available to plants until organic matter is mineralized or phosphorus is transferred to the host plant by arbuscular mycorrhizal fungi.<ref>{{cite journal |last1=Miyasaka |first1=Susan C. |last2=Habte |first2=Mitiku |year=2001 |title=Plant mechanisms and mycorrhizal symbioses to increase phosphorus uptake efficiency |journal=Communications in Soil Science and Plant Analysis |volume=32 |issue=7–8 |pages=1101–47 |doi=10.1081/CSS-100104105 |url=https://z-library.ec/book/Q9aKARB6X5 |access-date=14 May 2026 }}</ref> Agricultural fields may need to be fertilised to make up for the phosphorus that has been removed in the crop, but care must be taken that no surplus accumulates in soil in the long term.<ref>{{cite journal |last1=Gu |first1=Yu |last2=Ros |first2=Gerard H. |last3=Zhu |first3=Qichao |last4=Zheng |first4=Dongfang |last5=Shen |first5=Jianbo |last6=Cai |first6=Zejiang |last7=Xu |first7=Minggang |last8=De Vries |first8=Wim |date=1 November 2023 |title=Responses of total, reactive and dissolved phosphorus pools and crop yields to long-term fertilization |journal=Agriculture, Ecosystems & Environment |volume=357 |article-number=108658 |doi=10.1016/j.agee.2023.108658 |url=https://edepot.wur.nl/635338 |access-date=14 May 2026 }}</ref>

When phosphorus does form solubilised ions of H₂PO₄⁻, if not taken up by plant roots these ions rapidly form insoluble calcium phosphates or hydrous oxides of iron and aluminium. Phosphorus is largely immobile in the soil and is not leached but actually builds up in the organic surface layer if not cropped.<ref>{{cite journal |last1=Liu |first1=Jin |last2=Hu |first2=Yongfeng |last3=Yang |first3=Jianjun |last4=Abdi |first4=Daiel |last5=Cade-Menun |first5=Barbara J. |date=26 November 2014 |title=Investigation of soil legacy phosphorus transformation in long-term agricultural fields using sequential fractionation, P K-edge XANES and solution P NMR spectroscopy |journal=Environmental Science & Technology |volume=49 |issue=1 |pages=168–76 |doi=10.1021/es504420n |url=https://www.researchgate.net/publication/268878597 |access-date=15 May 2026 }}</ref> The application of soluble fertilizers to soils may result in zinc deficiencies as zinc phosphates form, but soil pH levels, partly depending on the form of phosphorus in the fertiliser, strongly interact with this effect, in some cases resulting in increased zinc availability.<ref>{{cite journal |last1=Lambert |first1=Raphaël |last2=Grant |first2=Cynthia |last3=Sauvé |first3=Sébastien |date=June 2007 |title=Cadmium and zinc in soil solution extracts following the application of phosphate fertilizers |journal=Science of the Total Environment |volume=378 |issue=3 |pages=293–305 |url=https://www.researchgate.net/publication/51382178 |doi=10.1016/j.scitotenv.2007.02.008 |pmid=17400282 |bibcode=2007ScTEn.378..293L |access-date=15 May 2026 }}</ref> Lack of phosphorus may interfere with the normal opening of the plant leaf stomata, decreased stomatal conductance resulting in decreased photosynthesis and respiration rates<ref>{{cite journal |last1=Terry |first1=Norman |last2=Ulrich |first2=Albert |date=January 1973 |title=Effects of phosphorus deficiency on the photosynthesis and respiration of leaves of sugar beet |journal=Plant Physiology |volume=51 |issue=1 |pages=43–7 |doi=10.1104/pp.51.1.43 |pmid=16658294 |pmc=367354 |doi-access=free }}</ref> while decreased transpiration increases plant temperature.<ref>{{cite journal |last1=Pallas |first1=James E. Jr |last2=Michel |first2=B.E. |last3=Harris |first3=D.G. |date=January 1967 |title=Photosynthesis, transpiration, leaf temperature, and stomatal activity of cotton plants under varying water potentials |journal=Plant Physiology |volume=42 |issue=1 |pages=76–88 |doi=10.1104/pp.42.1.76 |pmid=16656488 |pmc=1086491 |doi-access=free }}</ref> Phosphorus is most available when soil pH is 6.5 in mineral soils,<ref>{{cite journal |last1=Penn |first1=Chad J. |last2=Camberato |first2=James J. |date=8 June 2019 |title=A critical review on soil chemical processes that control how soil pH affects phosphorus availability to plants |journal=Agriculture |volume=9 |issue=6 |article-number=120 |doi=10.3390/agriculture9060120 |doi-access=free }}</ref> and 5.5 in organic soils.<ref>{{cite journal |last1=Lucas |first1=R. E. |last2=Davis |first2=J. F. |date=September 1961 |title=Relationships between pH values of organic soils and availabilities of 12 plant nutrients |journal=Soil Science |volume=92 |issue=3 |pages=177–82 |url=https://z-library.ec/book/r9v2QwJW90 |doi=10.1097/00010694-196109000-00005 |access-date=15 May 2026 }}</ref>

==Potassium==

The amount of potassium in a soil ranges between 3 and 100 tons per hectare in the upper 20 cm of the soil profile, of which only 2 per cent is available for plant growth.<ref>{{cite journal |last1=Mouhamad |first1=Raghad |last2=Alsaede |first2=Ameera |last3=Iqbal |first3=Munawar |date=March 2016 |title=Behavior of potassium in soil: a mini review |journal=Chemistry International |volume=2 |issue=1 |pages=58–69 |url=https://www.researchgate.net/publication/310842288 |doi=10.13140/RG.2.1.4830.7041 |access-date=15 May 2026 }}</ref> Common mineral sources of potassium are the mica biotite and potassium feldspar, KAlSi₃O₈.<ref>{{cite journal |last=Manning |first=David A. C. |date=30 July 2012 |title=Mineral sources of potassium for plant nutrition: a review |journal=Agronomy for Sustainable Development |volume=30 |issue=2 |pages=281–94 |url=https://z-library.ec/book/Z9kWgAva9O |doi=10.1051/agro/2009023 |access-date=15 May 2026 }}</ref> Rhizosphere bacteria, also called rhizobacteria, contribute through the production of organic acids to its solubilization.<ref>{{cite journal |last1=Meena |first1=Vijay Singh |last2=Maurya |first2=Bihari Ram |last3=Verma |first3=Jai Prakash |last4=Aeron |first4=Abhinav |last5=Kumar |first5=Ashok |last6=Kim |first6=Kangmin |last7=Bajpai |first7=Vivek K. |date=August 2015 |title=Potassium solubilizing rhizobacteria (KSR): isolation, identification, and K-release dynamics from waste mica |journal=Ecological Engineering |volume=81 |pages=340–7 |url=https://www.researchgate.net/publication/275045382 |doi=10.1016/j.ecoleng.2015.04.065 |bibcode=2015EcEng..81..340M |access-date=15 May 2026 }}</ref> When solubilised, half will be held as exchangeable cations on clay minerals while the other half is in the soil water solution.<ref>{{cite journal |last=Sharpley |first=Andrew N. |date=July–August 1989 |title=Relationship between soil potassium forms and mineralogy |journal=Soil Science Society of America Journal |volume=53 |issue=4 |pages=1023–8 |url=https://z-library.ec/book/jL5bdJAO9g |doi=10.2136/sssaj1989.03615995005300040006x |access-date=15 May 2026 }}</ref> Potassium fixation often occurs when soils dry and the potassium is bonded between layers of 2:1 expansive clay minerals such as illite, vermiculite or montmorillonite.<ref>{{cite journal |last=Sawhney |first=Brij L. |date=April 1972 |title=Selective sorption and fixation of cations by clay minerals: a review |journal=Clays and Clay Minerals |volume=20 |issue=2 |pages=93–100 |doi=10.1346/CCMN.1972.0200208 |bibcode=1972CCM....20...93S |s2cid=101201217 |url=https://z-library.ec/book/4yN0K71ELw |access-date=15 May 2026 }}</ref> Under certain conditions, dependent on the soil texture, intensity of drying, and initial amount of exchangeable potassium, the fixed percentage may be as much as 90&nbsp;percent within ten minutes.<ref>{{cite journal |last1=Stanford |first1=George |last2=Pierre |first2=W. H. |year=1947 |title=The relation of potassium fixation to ammonium fixation |journal=Soil Science Society of America Proceedings |volume=11 |issue=C |pages=155–60 |url=https://z-library.ec/book/nLGDQPgo9w |doi=10.2136/sssaj1947.036159950011000C0029x |access-date=15 May 2026 }}</ref> Potassium is easily leached, and thus lost for plant growth, from soils low in clay, except if manuring or liming compensates for poor cation-exchange capacity of the mineral soil.<ref>{{cite journal |last1=Yakovleva |first1=Lyudmila V. |last2=Danilov |first2=Dmitry A. |last3=Nikolaeva |first3=E. A. |year=2020 |title=Effect of mineral and organic fertilizers on potassium leaching in sandy loam soils |journal=IOP Conference Series, Materials Science and Engineering |volume=828 |article-number=012032 |doi=10.1088/1757-899X/828/1/012032 |doi-access=free }}</ref>

==Calcium==

Calcium is generally available but may be low as it is soluble and can be leached.<ref>{{cite journal |last1=Ritchey |first1=K. Dale |last2=Souza |first2=Djalma M. G. |last3=Lobato |first3=Edson |last4=Correa |first4=Osni |date=January–February 1980 |title=Calcium leaching to increase rooting depth in a Brazilian savannah Oxisol |journal=Agronomy Journal |volume=72 |issue=1 |pages=40–4 |url=https://z-library.ec/book/5X0jBVxq9r |doi=10.2134/agronj1980.00021962007200010009x |access-date=15 May 2026 }}</ref> It is thus low in sandy and heavily leached soil or strongly acidic mineral soils, resulting in excessive concentration of free hydrogen ions in the soil solution, and therefore these soils require liming.<ref>{{cite journal |last=Loide |first=Valli |year=2004 |title=About the effect of the contents and ratios of soil's available calcium, potassium and magnesium in liming of acid soils |journal=Agronomy Research |volume=2 |issue=1 |pages=71–82 |s2cid=28238101 |url=https://agronomy.emu.ee/vol021/p2109.pdf |archive-url=https://web.archive.org/web/20200807082057/https://pdfs.semanticscholar.org/8575/095acf2d519f637307d12ef3cf96d06050c3.pdf |url-status=live |archive-date=7 August 2020 |access-date=15 May 2026 }}</ref> Calcium is supplied to the plant in the form of exchangeable ions and moderately soluble minerals.<ref>{{cite journal |last=Kirkby |first=Ernest A. |year=1979 |title=Maximizing calcium uptake by plants |journal=Communications in Soil Science and Plant Analysis |volume=10 |issue=1–2 |pages=89–113 |url=https://z-library.ec/book/gyxlzBWgyo |access-date=15 May 2026 }}</ref> There are four main forms of calcium in the soil, among many others. Soil calcium can be in insoluble forms such as calcite, dolomite, in the soil solution in the form of a divalent cation or retained in exchangeable form at the surface of mineral and organic particles.<ref>{{cite journal |last=McLean |first=Eugene O. |year=1975 |title=Calcium levels and availabilities in soils |journal=Communications in Soil Science and Plant Analysis |volume=6 |issue=3 |pages=219–32 |url=https://z-library.ec/book/vyd7e5j29V |access-date=18 May 2026 }}</ref> Another main form is when calcium complexes with organic matter, forming covalent bonds between organic compounds which contribute to structural stability.<ref>{{cite journal |last1=Wuddivira |first1=Mark N. |last2=Camps-Roach |first2=Geremy |date=June 2007 |title=Effects of organic matter and calcium on soil structural stability |journal=European Journal of Soil Science |volume=58 |issue=3 |pages=722–7 |url=https://www.academia.edu/15089690 |doi=10.1111/j.1365-2389.2006.00861.x |bibcode=2007EuJSS..58..722W |s2cid=97426847 |access-date=18 May 2026 }}</ref> Calcium is more available on the soil colloids than is potassium because the common mineral calcite, CaCO₃, is more soluble than potassium-bearing minerals such as feldspar.<ref>{{cite journal |last=Albrecht |first=William Albert |date=January 1943 |title=Potassium in the soil colloid complex and plant nutrition |journal=Soil Science |volume=55 |issue=1 |pages=13–22 |url=https://z-library.ec/book/pyMOBwZlLw |access-date=18 May 2026 }}</ref>

Calcium uptake by roots is essential for plant nutrition, contrary to an old tenet that it was luxury consumption.<ref>{{cite journal |last1=Smith |first1=Garth S. |last2=Cornforth |first2=Ian S. |year=1982 |title=Concentrations of nitrogen, phosphorus, sulphur, magnesium, and calcium in North Island pastures in relation to plant and animal nutrition |journal=New Zealand Journal of Agricultural Research |volume=25 |issue=3 |pages=373–87 |doi=10.1080/00288233.1982.10417901 |url=https://z-library.ec/book/w9JqJ3KALD |bibcode=1982NZJAR..25..373S |access-date=18 May 2026 }}</ref> Calcium is considered as an essential component of plant cell membranes, a counterion for inorganic and organic anions in the vacuole, and an intracellular messenger in the cytosol, playing a role in cellular ''learning'' and ''memory''.<ref>{{cite journal |last1=White |first1=Philip J. |last2=Broadley |first2=Martin R. |date=October 2003 |title=Calcium in plants |journal=Annals of Botany |volume=92 |issue=4 |pages=487–511 |doi=10.1093/aob/mcg164 |pmid=12933363 |pmc=4243668 |url=https://z-library.ec/book/4yNwGaovXw |access-date=18 May 2026 }}</ref>

==Magnesium==

Magnesium is one of the dominant exchangeable cations in most soils (after calcium and potassium). Magnesium is an essential element for plants, microbes and animals, being involved in many catalytic reactions and in the synthesis of chlorophyll. Primary minerals that weather to release magnesium include hornblende, biotite and vermiculite.<ref>{{cite journal |last1=Ferreira |first1=Lusiane de Sousa |last2=Oliveira |first2=Vinicius de Souza |last3=Marchiori |first3=Johnatan Jair de Paula |last4=Ferreira |first4=Tatiane Cristovam |last5=Bernabé |first5=Ana Clara Bayer |last6=Boone |first6=Gilcéa Teixeira Fontana |last7=Pereira |first7=Luan Luciano dos Santos |last8=Carriço |first8=Eduarda |date=5 April 2023 |title=The nutrient magnesium in soil and plant: a review |journal=International Journal of Plant & Soil Science |volume=35 |issue=8 |pages=136–44 |doi=10.9734/IJPSS/2023/v35i82890 |url=https://www.researchgate.net/publication/369833218 |access-date=18 May 2026 }}</ref> Soil magnesium concentrations are generally sufficient for optimal plant growth, but highly weathered and sandy soils may be magnesium deficient due to leaching by heavy precipitation.<ref name="Roy2006"/>

==Sulfur==

Most sulfur is made available to plants, like phosphorus, by its release from decomposing organic matter.<ref>{{cite journal |last1=McGill |first1=William B. |last2=Cole |first2=Cory Vernon |date=November 1981 |title=Comparative aspects of cycling of organic C, N, S and P through soil organic matter |journal=Geoderma |volume=26 |issue=4 |pages=267–86 |doi=10.1016/0016-7061(81)90024-0 |url=https://z-library.ec/book/r98VRd2EXD |access-date=18 May 2026 }}</ref> Deficiencies may exist in some soils (especially sandy soils) and if cropped, sulfur needs to be added.<ref>{{cite web |last1=Camberato |first1=Jim |last2=Casteel |first2=Shaun |date=11 July 2017 |title=Sulfur deficiency |website=Purdue University |location=West Lafayette, Indiana |url=https://ioccorp.com/wp-content/uploads/2020/04/Sulfur-Deficiency-In-Soil.pdf |access-date=18 May 2026 }}</ref> The application of large quantities of nitrogen to fields that have marginal amounts of sulfur may cause sulfur deficiency by a ''dilution effect'' when stimulation of plant growth by nitrogen increases the plant demand for sulfur.<ref>{{cite book |last1=Jarrell |first1=Wesley M. |last2=Beverly |first2=Reuben B. |year=1981 |chapter=The dilution effect in plant nutrition studies |title=Advances in agronomy |volume=34 |editor-last=Brady |editor-first=Nyle C. |pages=197–224 |doi=10.1016/S0065-2113(08)60887-1 |isbn=9780120007349 |chapter-url=https://z-library.ec/book/mX4QnlbELx |access-date=18 May 2026 }}</ref> Being mainly bonded to carbon, sulfur abundance decreases with depth according to a concomitant decrease in soil organic matter content.<ref>{{cite journal |last1=Schroth |first1=Andrew W. |last2=Bostick |first2=Benjamin C. |last3=Graham |first3=Margaret |last4=Kaste |first4=James M. |last5=Mitchell |first5=Myron J. |last6=Friedland |first6=Andrew J. |date=December 2007 |title=Sulfur species behavior in soil organic matter during decomposition |journal=Journal of Geophysical Research, Biogeosciences |volume=112 |issue=G4 |article-number=G04011 |doi=10.1029/2007JG000538 |url=https://www.academia.edu/19462013 |access-date=18 May 2026 }}</ref>

==Micronutrients==

The micronutrients essential in plant life, in their order of importance, include chlorine, iron, manganese, boron, zinc, copper, and molybdenum.<ref>{{cite book |last1=George |first1=Edwin F. |last2=Hall |first2=Michael A. |last3=De Klerk |first3=Geert-Jan |year=2008 |chapter=The components of plant tissue culture media. I. Macro- and micro-nutrients |title=Plant propagation by tissue culture, Volume 1, The background |editor-last1=George |editor-first1=Edwin F. |editor-last2=Hall |editor-first2=Michael A. |editor-last3=De Klerk |editor-first3=Geert-Jan |pages=65–113 |doi=10.1007/978-1-4020-5005-3_3 |isbn=978-1-4020-5005-3 |chapter-url=https://www.researchgate.net/publication/226836015 |access-date=18 May 2026 }}</ref> The term refers to plants' needs, not to their abundance in soil. They are required in very small amounts but are essential to plant health in that most are required parts of enzyme systems which are involved in plant metabolism.<ref>{{cite journal |last=Welsh |first=Ross M. |year=1995 |title=Micronutrient nutrition of plants |journal=Critical Reviews in Plant Sciences |volume=14 |issue=1 |pages=49–82 |url=https://www.researchgate.net/publication/273041246 |doi=10.1080/713608066 |access-date=18 May 2026 }}</ref> They are generally available in the mineral component of the soil, but the heavy application of phosphates can cause a deficiency in zinc and iron by the formation of insoluble zinc and iron phosphates.<ref>{{cite book |last1=Summer |first1=Malcolm E. |last2=Farina |first2=Mart P. W. |year=1986 |chapter=Phosphorus interactions with other nutrients and lime in field cropping systems |title=Advances in soil science |volume=5 |pages=201–36 |editor-last=Stewart |editor-first=Bobby A. |publisher=Springer |location=New York, New York |isbn=978-1-4613-8660-5 |chapter-url=https://www.researchgate.net/publication/286120267 |doi=10.1007/978-1-4613-8660-5_5 |access-date=18 May 2026 }}</ref> Iron deficiency, stemming in plant chlorosis and rhizosphere acidification, may also result from excessive amounts of heavy metals or calcium minerals (liming|lime) in the soil.<ref>{{cite journal |last1=Lešková |first1=Alexandra |last2=Giehl |first2=Ricardo F.H. |last3=Hartmann |first3=Anja |last4=Fargašová |first4=Agáta |last5=von Wirén |first5=Nicolaus |date=July 2017 |title=Heavy metals induce iron deficiency responses at different hierarchic and regulatory levels |journal=Plant Physiology |volume=174 |issue=3 |pages=1648–68 |doi=10.1104/pp.16.01916 |pmid=28500270 |pmc=5490887 |url=https://www.researchgate.net/publication/316907982 |access-date=18 May 2026 }}</ref><ref>{{cite journal |last1=M’Sehli |first1=Wissal |last2=Youssfi |first2=Sabah |last3=Donnini |first3=Silvia |last4=Dell’Orto |first4=Marta |last5=De Nisi |first5=Patricia |last6=Zocchi |first6=Graziano |last7=Abdelly |first7=Chedly |last8=Gharsalli |first8=Mohamed |date=14 June 2008 |title=Root exudation and rhizosphere acidification by two lines of ''Medicago ciliaris'' in response to lime-induced iron deficiency |journal=Plant and Soil |volume=312 |issue=151 |pages=151–62 |url=https://www.academia.edu/18062153 |doi=10.1007/s11104-008-9638-9 |bibcode=2008PlSoi.312..151M |s2cid=12585193 |access-date=18 May 2026 }}</ref> Excess amounts of soluble boron, molybdenum and chloride are toxic.<ref>{{cite journal |last1=Jackson |first1=Marcus B. |last2=Lee |first2=Chiwon W. |last3=Schumacher |first3=Matthew A. |last4=Duysen |first4=Murray E. |last5=Self |first5=James R. |last6=Smith |first6=Ronald C. |year=1995 |title=Micronutrient toxicity in buffalograss |journal=Journal of Plant Nutrition |volume=18 |issue=6 |pages=1337–49 |doi=10.1080/01904169509364984 |url=https://z-library.ec/book/WyrGavR3XJ |access-date=18 May 2026 }}</ref>

==Non-essential nutrients==

Nutrients which enhance the health but whose deficiency does not stop the life cycle of plants include: cobalt, strontium, vanadium, silicon and nickel.<ref>{{cite journal |last1=Pereira |first1=B.F. Faria |last2=He |first2=Zhenli |last3=Stoffella |first3=Peter J. |last4=Montes |first4=Celia R. |last5=Melfi |first5=Adolpho J. |last6=Baligar |first6=Virupax C. |date=May 2012 |title=Nutrients and nonessential elements in soil after 11 years of wastewater irrigation |journal=Journal of Environmental Quality |volume=41 |issue=3 |pages=920–7 |url=https://www.researchgate.net/publication/224917711 |access-date=18 May 2026 |doi=10.2134/jeq2011.0047 |pmid=22565273 |bibcode=2012JEnvQ..41..920P }}</ref> As their importance is evaluated they may be added to the list of essential plant nutrients, as is the case for silicon.<ref>{{cite journal |last1=Richmond |first1=Kathryn E. |last2=Sussman |first2=Michael |date=June 2003 |title=Got silicon? The non-essential beneficial plant nutrient |journal=Current Opinion in Plant Biology |volume=6 |issue=3 |pages=268–72 |url=https://z-library.ec/book/mX4oBPVbyx |access-date=18 May 2026 |doi=10.1016/S1369-5266(03)00041-4 |pmid=12753977 |bibcode=2003COPB....6..268R }}</ref>

==See also== * Alkali soil * Sodic soils * Cation-exchange capacity * Soil contamination * Soil fertility * Index of soil-related articles

==References== {{reflist}}

==Bibliography== {{refbegin}} * {{cite web |title=Arizona Master Gardener Manual |url=https://z-library.ec/book/JLZMOOEvX8 |publisher=Arizona Cooperative Extension, College of Agriculture, University of Arizona |access-date=18 May 2026 }} * {{cite book |title=Soil: The Yearbook of Agriculture 1957 |last=Stefferud |first=Alfred |year=1957 |publisher=United States Department of Agriculture |url=https://nmwrri.nmsu.edu/footer_pages/nm-wrri-library-database-files/wrri-library-pdfs/wrrilibrary2/002456.pdf |oclc=704186906 |access-date=18 May 2026 }} {{refend}}

Category:Soil Category:Plant nutrition