High Organic Soil v. Low Organic Soil

Credit | Spectrum Analytic Agronomic Library

Cation exchange Capacity fact sheet from Cornell University.
The capacity of the soil to hold on to positively charged ions in the soil is called the cation exchange capacity (CEC). Examples of cations include calcium (Ca2+), magnesium (Mg2+), and potassium (K+), sodium (Na+). According to the fact sheet, sandy soils low in organic matter have a very low CEC (less than 3 cmolc/kg) while heavier clay soils or soils high in organic matter generally have a much higher CEC (greater than 20 cmolc/kg). The study goes on to say, “The higher the CEC the more clay or organic matter present in the soil. This usually means that high CEC (clay) soils have a greater water holding capacity than low CEC (sandy) soils.” This implies a direct relation between high cation exchange capacity and increased moisture retention of soil. Typical estimates of CEC of different soils is given below:

General description
CEC (cmolc/kg soil)

CEC 25! Fine-textured soils developed from clayey lake sediments and medium- to fine-textured soils developed from lake sediments

CEC 20 Medium- to fine-textured soils developed from calcareous glacial
till, medium-textured to moderately fine-textured soils developed from slightly calcareous glacial till mixed with shale, and medium-textured soils developed in recent alluvium.

CEC 18 Moderately coarse textured soil developed from glacial outwash
and recent alluvium and medium textured acid soil developed on
glacial till

CEC 16 Coarse- to medium-textured soils formed from glacial till or glacial outwash.

CEC 12 Coarse- to very coarse-textured soils formed from gravelly or sandy glacial outwash or glacial lake beach ridges or deltas.

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*Elemite, a 100% montmorillonite clay based soil amendment is used by organic farmers in lieu of fertilizer to increase CEC in their soil. Elemite also promotes increase microbial activity in soil.