Cation-exchange capacity (CEC) is an index of the soil's capacity to exchange cations with the soil solution. It affects the ability of the soil to adsorb and retain cations and heavy metals. Cations are held to the soil particles by adsorption and can be returned to the soil solution for plant use by the exchange process.
Soils that have high CEC and organic soils can exchange and retain large amounts of cations released by agricultural waste mineralization processes. Conversely, soils in which the CEC is low have low potential for exchanging and retaining these agricultural waste materials. The potential for agricultural waste contamination of underlying ground water and aquifers is highest for soils that have low CEC and lowest for those with high CEC.
The limitations for solid and liquid waste applications are slight for soils that have a cation-exchange capacity of more than 15, moderate for those with a capacity of 5 to 15, and severe for those for which it is less than 5. Underlying ground water supplies and aquifers can become contaminated when agricultural wastes are applied at high rates to soils that have moderate or severe limitations because of their CEC. Reducing agricultural waste application rates can reduce the hazard for ground water contamination.
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