Cation Saturation and Nutrient Absorption by Plants
The availability of adsorbed cations is not always so easy as the above explanation might suggest. This is because, several factors operate to expedite or retard the release of nutrients. First, there is the proportion of the cation exchange capacity of the soil occupied by the nutrient cation in question. For instance, if the percentage calcium saturation of a soil is high, the displacement of this cation is easy and rapid. Thus 6 milliequivalents of exchangeable calcium in a soil whose exchange capacity probably would mean ready availability. In another case 6 milliequivalents of Ca on the exchange complex in a soil having a total exchange capacity may represent an opposite condition. This is for this reason liming for alfa alfa crop (requires abundant calcium) should exceed 90 per cent
saturation with calcium.