Cation Exchange and Its Role in Soil Fertility
Cation exchange is an important soil chemical property. Cation exchange is derived from negative charges on soil clay and organic matter particles that attract positively charged elements, or cations. The total capacity of the soil to hold cations, measured in units of negative charge per unit of soil, is called “cation exchange capacity”, or CEC. It influences the soils ability to hold certain nutrients like potassium (K+), calcium (Ca2+), magnesium (Mg2+), or ammonium-nitrogen (NH4+), but also takes into account soil acidity as aluminum (Al3+) and hydrogen (H+). Coarse-textured, sandy soils have relatively low CEC because they have low clay content and typically low organic matter content. High-clay or high organic-matter soils have relatively high CEC.
Cation exchange capacity can give an indication of soil texture and is often an indicator of general soil fertility. Furthermore, base saturation is the percentage of the CEC occupied by what are called “basic” cations, as opposed to cations of an acidic nature. The basic cations usually considered in soil fertility are Ca2+, Mg2+, K+, and Na+ (sodium). In some cases, the base-saturation percentage of a nutrient gives an approximation of the supply of that nutrient relative to other basic cations. The role of base saturation in crop fertilizer recommendations is often misunderstood and misused.
Listen to University of Minnesota soil scientists discuss cation exchange, base saturation, and their role in soil fertility.
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