Three considerations are involved in determining soil needs for three major cations:

1. The Cation Exchange Capacity.

Different soils hold by absorption different total amounts of potassium, calcium, magnesium, sodium, hydrogen and other cations. This total absorbed amount, called Cation Exchange Capacity, depends on the kinds and amounts of clay, silt, sand, and organic matter in the soil.

2. The Ratio of these Elements.

Change the ratios among the elements within this total to achieve an adequate blend of the three nutritionally important cations (K, Ca, Mg).

3. The Degree of Saturation Desired.

In most instances it is not necessary nor economically desirable to completely saturate the exchange complex with the changeable base elements. Economic response ceases when the crop need for nutrient base elements is satisfied or nearly satisfied. This normally occurs well before the saturation point of the exchange capacity is reached. A 75-90% saturation of the exchange capacity with a balanced ratio of exchangeable bases will usually be completely adequate for high yields of most crops.

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