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Understanding the Cation Exchange Capacity (CEC) of your Soil

Cation Exchange Capacity (CEC) is a measure of your soil’s ability to hold onto nutrients –  It is influenced by the presence of negatively charged clay and organic matter, which attract positively charged ions (cations) like Calcium, Potassium, Hydrogen, Sodium, and Magnesium.

Think of CEC as a parking lot, where a high CEC soil has many parking spots for cations, and a low CEC soil has only a few. A soil with high CEC can hold and exchange more nutrients than soil with low CEC.

CEC is a starting point for determining base saturation. While CEC refers to the soil’s ability to hold nutrients, base saturation indicates how many of those parking spots are currently occupied. Soil tests often measure CEC first, as it provides a quick assessment of the soil’s nutrient-holding capacity and texture (sandy vs. clay). 

CEC is especially important when applying nutrients like Nitrogen and Sulfur, because it can be used to estimate how much should be applied at once. The CEC also impacts the timing of nutrient applications. In some regions, Nitrogen can be applied in the fall for use in the spring, but in areas with sandy soils and low CEC, Nitrogen may need to be split-applied to reduce the risk of environmental loss.