Editing Soil (section)

====Buffering====
{{Further|Soil conditioner}}
The resistance of soil to change in pH, as a result of the addition of acid or basic material, is a measure of the [[buffering capacity]] of a soil and (for a particular soil type) increases as the [[Cation-exchange capacity|CEC]] increases. Hence, pure sand has almost no buffering ability, though soils high in [[Colloid|colloids]] (whether mineral or organic) have high buffering capacity.<ref>{{cite journal |last1=Sposito |first1=Garrison |last2=Skipper |first2=Neal T. |last3=Sutton |first3=Rebecca |last4=Park |first4=Sun-Ho |last5=Soper |first5=Alan K. |last6=Greathouse |first6=Jeffery A. |year=1999 |title=Surface geochemistry of the clay minerals |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=96 |issue=7 |pages=3358–64 |doi=10.1073/pnas.96.7.3358 |pmid=10097044 |pmc=34275 |bibcode=1999PNAS...96.3358S |doi-access=free }}</ref> Buffering occurs by cation exchange and [[Neutralization (chemistry)|neutralisation]]. However, colloids are not the only regulators of soil pH. The role of [[carbonates]] should be underlined, too.<ref>{{cite web |last=Sparks |first=Donald L. |title=Acidic and basic soils: buffering |url=https://lawr.ucdavis.edu/classes/ssc102/Section8.pdf |publisher=[[University of California, Davis]], Department of Land, Air, and Water Resources |location=Davis, California |access-date=9 March 2025 }}</ref> More generally, according to pH levels, several buffer systems take precedence over each other, from [[calcium carbonate]] [[buffer range]] to iron buffer range.<ref>{{cite book |last=Ulrich |first=Bernhard |title=Effects of accumulation of air pollutants in forest ecosystems |chapter=Soil acidity and its relations to acid deposition |date=1983 |chapter-url=https://archive.org/details/ulrich-1983 |pages=127–46 |edition=1st |editor-last1=Ulrich |editor-first1=Bernhard |editor-last2=Pankrath |editor-first2=Jürgen |publisher=[[D. Reidel Publishing Company]] |location=Dordrecht, The Netherlands |isbn=978-94-009-6985-8 |doi=10.1007/978-94-009-6983-4_10 |access-date=9 March 2025 }}</ref>

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

The addition of a small amount of [[liming (soil)|lime]], Ca(OH)<sub>2</sub>, will displace hydronium ions from the soil colloids, causing the fixation of calcium to colloids and the evolution of CO<sub>2</sub> and water, with little permanent change in soil pH.

The above are examples of the buffering of soil pH. The general principal is that an increase in a particular cation in the soil water solution will cause that cation to be fixed to colloids (buffered) and a decrease in solution of that cation will cause it to be withdrawn from the colloid and moved into solution (buffered). The degree of buffering is often related to the [[Cation-exchange capacity|CEC]] of the soil; the greater the CEC, the greater the buffering capacity of the soil.{{sfn|Donahue|Miller|Shickluna|1977|pp=120–121}}