Tutorial:Soil Leaching

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Leaching
Leaching is the loss of soluble material from the soil profile in percolating water. The effects of leaching are most noticeable on coarse grained, free-draining soils and in areas where rainfall exceeds evapotranspiration.



Leaching leads to the progressive acidification (lowering of soil pH) of topsoils as bases are lost. Many of the salts lost are important plant nutrients so excessive leaching can reduce soil fertility. However, a proportion of soil nutrients are bound to the surface of clays and organic matter and are available for plants to use, but are bound too tightly to be leached. This is known as the cation exchange capacity of a soil.

Leaching and acidification of soils and sediments has implications for the preservation of bone, shell and other calcareous materials as these materials are degraded in acid soil conditions. See table of favourable preservation conditions for different materials.

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