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Soil Test Interpretation Reference

What is Cation Exchange Capacity (CEC)?

Remember, the soil particles have a negative charge. Cations are positively charged. The CEC of a soil is the amount of free negative charge a soil has to hold in potential availability the positively charge cations. The positively charged cations are Calcium (Ca++), Magnesium (Mg++), Potassium (K=), Sodium (Na+), Hydrogen (H+), and Ammonia (NH4+). The higher the CEC, the heavier the soil will be, and the greater the ability to hold the cations in potential in potential availability. It is measured using the exchangeable or chemical testing procedure.

What are cations so important?

Cations carry a positive (+) charge. The soil carries a negative (-) charge. Cations are important in the soil for the following reason.

The positive charge (+) or the cation is attracted to the negative (-) charge of the soil particle. This electrical attraction allows for the soil particles to be held in close proximity to each other, thus giving the soil structure.

Is there an amount or ration of Cations that is desirable in the soil?

Each caton has a specific size or diameter. In order to create the proper distance between the soil particles, there needs to be a proper ratio of the cations. The ratios and levels of the cations have a profound impact on air and water movement, and nutrient availability. This level is measure by the exchangeable or chemical extracted soil test.

Where should the total soil levels (% of soil cations – both soluble and insoluble) be?

Calcium (Ca++) 73%
Higher percentages mean that the soil has a high reserve of calcium. Lower percentages mean that the soil has a low reserve of calcium.

Magnesium (Mg++) 15%
Higher magnesium does not mean that the turf will have good magnesium nutrition.
Higher magnesium soils (20% + range) tend to have water and air movement problems.

Potassium (K+) 5-8%
Higher or lower than this does not necessarily mean that K will be more or less available, it’s just a measure of the potential (reserve) potassium (K+) in the soil.