Editing Soil pH (section)

== Effect of soil pH on plant growth ==

=== Acid soils ===
High levels of aluminium occur near mining sites; small amounts of aluminium are released to the environment at the coal-fired power plants or [[Incineration|incinerators]].<ref name="ATSDR Public Health">{{cite web |url=https://www.atsdr.cdc.gov/ToxProfiles/tp22-c1-b.pdf |title=Public health statement for aluminum |website=www.atsdr.cdc.gov |language=en |date=September 2008 |access-date=12 March 2023 |archive-date=12 December 2016 |archive-url=https://web.archive.org/web/20161212212014/https://www.atsdr.cdc.gov/phs/phs.asp?id=1076&tid=34 |url-status=live}}</ref> Aluminium in the air is washed out by the rain or normally settles down but small particles of aluminium remain in the air for a long time.<ref name="ATSDR Public Health" />

Acidic [[precipitation]] is the main natural factor to mobilize aluminium from natural sources<ref name="Piero3">{{cite journal |last=Dolara |first=Piero |date=21 July 2014 |title=Occurrence, exposure, effects, recommended intake and possible dietary use of selected trace compounds (aluminium, bismuth, cobalt, gold, lithium, nickel, silver) |journal=[[International Journal of Food Sciences and Nutrition]] |volume=65 |issue=8 |pages=911–24 |doi=10.3109/09637486.2014.937801 |issn=1465-3478 |pmid=25045935 |s2cid=43779869 |url=https://lib-nhwjx7zkiyjoeipfyn7m37ed.late.re/book/35772390/5dc19c |access-date=12 March 2023}}</ref> and the main reason for the environmental effects of aluminium;<ref name="RosselandEldhuset1990">{{cite journal |last1=Rosseland |first1=Bjorn Olav |last2=Eldhuset |first2=Toril Drabløs |last3=Staurnes |first3=Magne |year=1990 |title=Environmental effects of aluminium |journal=Environmental Geochemistry and Health |volume=12 |issue=1–2 |pages=17–27 |doi=10.1007/BF01734045 |pmid=24202562 |bibcode=1990EnvGH..12...17R |s2cid=23714684 |issn=0269-4042 |url=https://www.researchgate.net/publication/258348898 |access-date=12 March 2023}}</ref> however, the main factor of presence of aluminium in salt and freshwater are the industrial processes that also release aluminium into air.<ref name="Piero3" /> Plants grown in acid soils can experience a variety of stresses including [[aluminium]]&nbsp;(Al), [[hydrogen]]&nbsp;(H), and/or [[manganese]]&nbsp;(Mn) toxicity, as well as nutrient deficiencies of [[calcium]]&nbsp;(Ca) and [[magnesium]]&nbsp;(Mg).<ref>{{cite book |title=The nature and properties of soils, global edition |edition=15th |year=2016 |last1=Weil |first1=Raymond R. |last2=Brady |first2=Nyle C. |isbn=9781292162232 |url=https://lib-nhwjx7zkiyjoeipfyn7m37ed.late.re/book/3515307/f40531 |access-date=19 March 2023 |publisher=[[Pearson Education]] |location=London, United Kingdom}}</ref>

[[Aluminium#Environmental effects|Aluminium toxicity]] is the most widespread problem in acid soils.  Aluminium is present in all soils to varying degrees, but dissolved Al<sup>3+</sup> is toxic to plants; Al<sup>3+</sup> is most soluble at low pH; above pH&nbsp;5.0, there is little Al in soluble form in most soils.<ref name="Kopittke2016">{{cite journal |last1=Kopittke |first1=Peter M. |last2=Menzies |first2=Neal W. |last3=Wang |first3=Peng |last4=Blamey |first4=F. Pax C. |title=Kinetics and nature of aluminium rhizotoxic effects: a review |journal=[[Journal of Experimental Botany]] |date=August 2016 |volume=67 |issue=15 |pages=4451–67 |doi=10.1093/jxb/erw233 |pmid=27302129 |url=https://articles-pdjrj4ripo5k3r4j2r4mhmo5.late.re/book/55935402/d61ab1 |access-date=19 March 2023}}</ref><ref>{{cite journal |last1=Hansson |first1=Karna |last2=Olsson |first2=Bengt A. |last3=Olsson |first3=Mats |last4=Johansson |first4=Ulf |last5=Kleja |first5=Dan Berggren |title=Differences in soil properties in adjacent stands of Scots pine, Norway spruce and silver birch in SW Sweden |journal=[[Forest Ecology and Management]] |date=August 2011 |volume=262 |issue=3 |pages=522–30 |doi=10.1016/j.foreco.2011.04.021 |url=https://www.academia.edu/16589041 |access-date=19 March 2023}}</ref> Aluminium is not a plant nutrient, and as such, is not actively taken up by the plants, but enters plant roots passively through [[osmosis]]. Aluminium can exist in many different forms and is a responsible agent for limiting growth in various parts of the world. Aluminium tolerance studies have been conducted in different plant species to see viable thresholds and concentrations exposed along with function upon exposure.<ref>{{cite journal |last1=Wright |first1=Robert J. |title=Soil aluminum toxicity and plant growth |journal=Communications in Soil Science and Plant Analysis |date=September 1989 |volume=20 |issue=15–16 |pages=1479–97 |doi=10.1080/00103628909368163 |bibcode=1989CSSPA..20.1479W |url=https://articles-pdjrj4ripo5k3r4j2r4mhmo5.late.re/book/21233659/9e6a73 |access-date=19 March 2023}}</ref> Aluminium inhibits root growth; lateral roots and root tips become thickened and roots lack fine branching; root tips may turn brown. In the root, the initial effect of Al<sup>3+</sup> is the inhibition of the expansion of the cells of the [[rhizodermis]], leading to their rupture; thereafter it is known to interfere with many physiological processes including the uptake and transport of calcium and other essential nutrients, cell division, cell wall formation, and enzyme activity.<ref name="Kopittke2016"/><ref>{{cite journal |last1=Rout |first1=Gyana Ranjan |last2=Samantaray |first2=Sanghamitra |last3=Das |first3=Premananda |title=Aluminium toxicity in plants: a review |journal=Agronomie |date=January 2001 |volume=21 |issue=1 |pages=3–21 |doi=10.1051/agro:2001105 |bibcode=2001AgSD...21....3R |url=https://hal.science/hal-00886101/document |access-date=19 March 2023}}</ref>

Proton (H<sup>+</sup> ion) stress can also limit plant growth. The [[proton pump]], H<sup>+</sup>-ATPase, of the [[plasmalemma]] of root cells works to maintain the near-neutral pH of their [[cytoplasm]]. A high proton activity (pH within the range 3.0–4.0 for most plant species) in the external growth medium overcomes the capacity of the cell to maintain the cytoplasmic pH and growth shuts down.<ref name="Shavrukov2016">{{cite journal |last1=Shavrukov |first1=Yuri |last2=Hirai |first2=Yoshihiko |title=Good and bad protons: genetic aspects of acidity stress responses in plants |journal=[[Journal of Experimental Botany]] |date=January 2016 |volume=67 |issue=1 |pages=15–30 |doi=10.1093/jxb/erv437 |pmid=26417020 |doi-access=free}}</ref>

In soils with a high content of [[manganese]]-containing minerals, Mn toxicity can become a problem at pH 5.6 and lower.  Manganese, like aluminium, becomes increasingly soluble as pH drops, and Mn toxicity symptoms can be seen at pH levels below 5.6.  Manganese is an essential plant nutrient, so plants transport Mn into leaves.  Classic symptoms of Mn toxicity are crinkling or cupping of leaves.<ref>{{cite journal |last=Ramakrishnan |first=Palayanoor Sivaswamy |title=Nutritional requirements of the edaphic ecotypes in ''Melilotus alba'' Medic. II. Aluminium and manganese |journal=[[New Phytologist]] |date=April 1968 |volume=67 |issue=2 |pages=301–08 |doi=10.1111/j.1469-8137.1968.tb06385.x |doi-access=free}}</ref>

===Nutrient availability in relation to soil pH===
[[File:Soil-pH.svg|thumb|right|Nutrient availability in relation to soil pH<ref>{{cite book |first=Arnold |last=Finck |location=Kiel, Germany |year=1976 |title=Pflanzenernährung in Stichworten |publisher=Hirt |isbn=978-3-554-80197-2 |page=80}}</ref>]]

Soil pH affects the availability of some [[Plant nutrition|plant nutrients]]:

As discussed above, aluminium toxicity has direct effects on plant growth; however, by limiting root growth, it also reduces the availability of plant nutrients. Because roots are damaged, nutrient uptake is reduced, and deficiencies of the [[macronutrients]] (nitrogen, phosphorus, potassium, calcium and magnesium) are frequently encountered in very strongly acidic to ultra-acidic soils (pH<5.0).<ref name="Sumner2002">{{cite journal |last1=Sumner |first1=Malcolm E. |last2=Yamada |first2=Tsuioshi |title=Farming with acidity |journal=Communications in Soil Science and Plant Analysis |date=November 2002 |volume=33 |issue=15–18 |pages=2467–96 |doi=10.1081/CSS-120014461 |bibcode=2002CSSPA..33.2467S |s2cid=93165895}}</ref> When aluminum levels increase in the soil, it decreases the pH levels. This does not allow for trees to take up water, meaning they cannot photosynthesize, leading them to die. The trees can also develop yellowish colour on their leaves and veins.<ref>{{cite journal |last1=Cape |first1=J. N. |title=Direct damage to vegetation caused by acid rain and polluted cloud: definition of critical levels for forest trees |journal=[[Environmental Pollution (journal)|Environmental Pollution]] |date=1 January 1993 |volume=82 |issue=2 |pages=167–180 |doi=10.1016/0269-7491(93)90114-4 |pmid=15091786 |url=https://articles-pdjrj4ripo5k3r4j2r4mhmo5.late.re/book/19978680/d768f2 |access-date=2 April 2023}}</ref>

[[Plant nutrition#Molybdenum|Molybdenum]] availability is increased at higher pH; this is because the molybdate ion is more strongly sorbed by clay particles at lower pH.<ref name="Huang2011">{{cite book |last1=Bolan |first1=Nanthi |last2=Brennan |first2=Ross |last3=Budianta |first3=Dedik |last4=Camberato |first4=James J. |last5=Naidu |first5=Ravi |last6=Pan |first6=William L. |last7=Sharpley |first7=Andrew |last8=Sparks |first8=Donald L. |last9=Sumner |first9=Malcolm E. |editor1-last=Huang |editor1-first=Pan Ming |editor2-last=Li |editor2-first=Yuncong |editor3-last=Sumner |editor3-first=Malcolm E. |title=Handbook of soil sciences: resource management and environmental impacts |date=2012 |publisher=[[CRC Press]] |location=Boca Raton, Florida |isbn=978-1-4398-0308-0 |pages=11–1 to 11–80 |edition=2nd |chapter=Bioavailability of N, P, K, Ca, Mg, S, Si, and micronutrients |url=https://lib-nhwjx7zkiyjoeipfyn7m37ed.late.re/book/2214335/a4c9a4 |access-date=2 April 2023}}</ref>

[[Plant nutrition#Zinc|Zinc]], [[Plant nutrition#Iron|iron]], [[Plant nutrition#Copper|copper]] and [[Plant nutrition#Manganese|manganese]] show decreased availability at higher pH (increased [[sorption]] at higher pH).<ref name="Huang2011"/>

The effect of pH on [[Plant nutrition#Phosphorus|phosphorus]] availability varies considerably, depending on soil conditions and the crop in question. The prevailing view in the 1940s and 1950s was that P availability was maximized near neutrality (soil pH 6.5–7.5), and decreased at higher and lower pH.<ref name="Truog1946">{{cite book |last1=Truog |first1=Emil |title=Science in farming, USDA Yearbook, 1941–1947 |date=1946 |pages=566–76 |chapter=The liming of soils |chapter-url=https://naldc.nal.usda.gov/download/IND43893966/PDF |access-date=9 April 2023}}</ref><ref name="Sumner1986">{{cite book |last1=Sumner |first1=Malcolm E. |last2=Farina |first2=Mart P.W. |editor1-last=Stewart |editor1-first=Bob A. |title=Advances in soil science |date=1986 |publisher=[[Springer Publishing|Springer]] |location=New York, New York |isbn=978-1-4613-8660-5 |pages=201–36 |chapter=Phosphorus interactions with other nutrients and lime in field cropping systems |doi=10.1007/978-1-4613-8660-5_5 |chapter-url=https://www.researchgate.net/publication/286120267 |access-date=9 April 2023}}</ref> Interactions of phosphorus with pH in the moderately to slightly acidic range (pH 5.5–6.5) are, however, far more complex than is suggested by this view. Laboratory tests, glasshouse trials and field trials have indicated that increases in pH within this range may increase, decrease, or have no effect on P availability to plants.<ref name="Sumner1986"/><ref name="Haynes1982">{{cite journal |last1=Haynes |first1=R. J. |title=Effects of liming on phosphate availability in acid soils: a critical review |journal=[[Plant and Soil]] |date=October 1982 |volume=68 |issue=3 |pages=289–308 |doi=10.1007/BF02197935 |s2cid=22695096 |url=https://articles-pdjrj4ripo5k3r4j2r4mhmo5.late.re/book/6871474/3b010d |access-date=9 April 2023}}</ref>