Humus cation exchange capacity

The acidity of the soil may conveniently be characterized by the content of metal ions, relative to the total cation exchange capacity of the soil. In the acid types of soil considered here, this base saturation degree is usually below 10%. The degree of base saturation will be reduced when (1) the roots take up exchangeable cations from the soil, and (2) when accumulation of dead plant material increases the amount of humus, and thereby the cation exchange capacity. To a certain degree, both of these processes are reversible, but if plant products are removed from the area without application of fertilizers, manure or lime, this represents an acidification by reducing the available supply of cations. 

In the preceding chapter frequent reference was made to the role played by soil organic matter as a cation exchange material, and to its ability to chelate nutrients. It is also an excellent buffer. Since thes properties account for many of the most important benefits derived from its presence in soil it is well to consider at some length just what is meant by these terms, and how and to what extent humus functions in these processes. Since plant roots also possess cation exchange capacities that in many respects resemble those of soil organic matter, reference will also be made to this phase of ion exchange. 

Soils vary widely in their ability to retain cations. Soils with a high clay/humus content have a high cation exchange capacity/ because they have an abundance of exchange sites. 

Lignin plays an important role in the carbon cycle by sequestering atmospheric carbon into living vegetation. It is one of the components of dead vegetation that will decompose last. The resulting soil humus provides increased cation exchange capacity and expands moisture retention. 

Lignin, one of the most slowly decomposing components of dead vegetation, plays an important role in the carbon cycle by contributing to the production of humus, which increases cation exchange capacity in the soil. 

Cation exchange Total acidities of isolated fractions of humus range from 3000 to 14 000 mmole kg-1 Increases the cadon exchange capacity (CEC) of the soil from 20 to 70% of the CEC of many soils is caused by organic matter... 

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