Liming

The development of soil acidity is a naturally occurring process in humid temperate climates. In humid regions where precipitation is high enough, soils become acidic because of the leaching of calcium, magnesium, potassium, and other exchangeable bases from the surface layers. This leaching leaves behind exchangeable hydrogen and aluminum, which are acids in mineral soils. Except in regions of low precipitation, where leaching of soils does not occur and where a net movement of bases is upward rather than downward, acidification of soils is a natural process or is a process associated with crop production. In cultivated land, acidity also develops from the oxidation of complex organic matter into organic acids. Some fertilizers, particularly ammonium-containing chemical or organic fertilizers and carbon-based organic fertilizers lead to acidification of soils. Cation absorption (Ca²⁺, Mg²⁺, K⁺, NH₄ ⁺) in excess of anion absorption (NO₃ ^–, SO₄ ^2–, H₂PO₄ ^–) by plants also leads to a net production of acidity by the roots. Cation absorption leads to depletion of ions from exchange sites in soil and to the development of acidity.