Understanding Soil Cation Exchange Capacity

By Marcus Williams · October 15, 2026

What Is Cation Exchange Capacity?

Cation exchange capacity (CEC) measures how many positively charged nutrient ions—calcium, magnesium, potassium, ammonium—a soil can hold and release to plant roots. It is one of the most important indicators of soil fertility.

How CEC Works

Clay particles and organic matter carry negative charges that attract and hold positive nutrient ions. Sandy soils with little clay or organic matter have low CEC (1-5 meq/100g), meaning nutrients leach quickly. Clay soils can have CEC values of 25-40 or higher.

CEC and Soil Management

Low CEC soils need more frequent, smaller fertilizer applications because they cannot store nutrients. High CEC soils hold nutrients well but may require more fertilizer initially to "fill" the exchange sites before plants benefit.

Improving CEC

Adding organic matter is the most practical way to raise CEC in home gardens. Each 1% increase in organic matter adds roughly 2 meq/100g of exchange capacity. Humus has a CEC of 150-300, far exceeding most clay minerals.

Understanding Soil Cation Exchange Capacity

What Is Cation Exchange Capacity?

How CEC Works

CEC and Soil Management

Improving CEC

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