Editing Soil pH (section)

===Increasing pH of acidic soil===
Finely ground [[agricultural lime]] is often applied to acid soils to increase soil pH ([[Liming (soil)|liming]]). The amount of [[limestone]] or [[chalk]] needed to change pH is determined by the [[Mesh (scale)|mesh]] size of the lime (how finely it is ground) and the [[Soil#Buffering|buffering capacity]] of the soil. A high mesh size (60 mesh = 0.25&nbsp;mm; 100 mesh = 0.149&nbsp;mm) indicates a finely ground lime that will react quickly with soil acidity. The buffering capacity of a soil depends on the clay content of the soil, the type of clay, and the amount of organic matter present, and may be related to the soil [[cation exchange capacity]].  Soils with high clay content will have a higher buffering capacity than soils with little clay, and soils with high organic matter will have a higher buffering capacity than those with low organic matter.<ref>{{cite journal |last1=Minhal |first1=Fibrianty |last2=Ma'as |first2=Aswar |last3=Hanudin |first3=Eko |last4=Sudira |first4=Putu |title=Improvement of the chemical properties and buffering capacity of coastal sandy soil as affected by clay and organic by-product application  |journal=Soil and Water Research |date=June 2020 |volume=15 |issue=2 |pages=93–100 |doi=10.17221/55/2019-SWR |url=https://www.old-aj.cz/publicFiles/55_2019-SWR.pdf |access-date=3 September 2023}}</ref> Soils with higher buffering capacity require a greater amount of lime to achieve an equivalent change in pH.<ref name="Aitken1990">{{cite journal |last1=Aitken |first1=R.L. |last2=Moody |first2=Philip W. |last3=McKinley |first3=P.G. |title=Lime requirement of acidic Queensland soils. I. Relationships between soil properties and pH buffer capacity |journal=[[Australian Journal of Soil Research]] |date=1990 |volume=28 |issue=5 |pages=695–701 |doi=10.1071/SR9900695 |url=https://www.publish.csiro.au/SR/SR9900695}}</ref> The buffering of soil pH is often directly related to the quantity of aluminium in soil solution and taking up exchange sites as part of the [[Cation-exchange capacity|cation exchange capacity]].  This aluminium can be measured in a soil test in which it is extracted from the soil with a salt solution, and then is quantified with a laboratory analysis.  Then, using the initial soil pH and the aluminium content, the amount of lime needed to raise the pH to a desired level can be calculated.<ref>{{cite journal |last=Bartlett |first=Richmond |date=1982 |title=Reactive aluminum in the Vermont Soil Test |journal=Communications in Soil Science and Plant Analysis |volume=13 |issue=7| pages=497–506 |doi=10.1080/00103628209367289 |bibcode=1982CSSPA..13..497B |url=https://www.tandfonline.com/doi/epdf/10.1080/00103628209367289}}</ref>

Amendments other than agricultural lime that can be used to increase the pH of soil include [[wood ash]], industrial calcium oxide ([[burnt lime]]), [[magnesium oxide]], [[basic slag]] ([[calcium silicate]]), and [[oyster]] shells.  These products increase the pH of soils through various [[acid–base reaction]]s. [[Calcium silicate]] neutralizes active acidity in the soil by reacting with H<sup>+</sup>&nbsp;ions to form [[Silicic acid|monosilicic acid]] (H<sub>4</sub>SiO<sub>4</sub>), a neutral solute.<ref name="VonUexkull1986">{{cite book |last1=von Uexkull |first1=H.R. |location=Rome, Italy |title=Efficient fertilizer use in acid upland soils of the humid tropics |date=1986 |publisher=[[Food and Agriculture Organization]] |isbn=9789251023877 |pages=16–22 |url=https://edepot.wur.nl/494356 |access-date=10 September 2023 |language=en |chapter=Lime and liming}}</ref>