Ion Exchange
The process of replacing one ion that is attached to a charged surface with another. A very important type of ion exchange is the exchange of cations bound to soil particles.
Soil clay minerals and organic matter both have negative surface charges that bind cations. In a fertile soil the predominant exchangeable cations are Ca2+, Mg2+ and K+. In acid soils Al3+ and H+ are also important exchangeable ions. When materials containing cations are added to soil, cations leaching through the soil are retarded by cation exchange.
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