INTERACTION BETWEEN PLANT NUTRIENTS .1. THEORY AND ANALYTICAL PROCEDURES

Synergism and antagonism cause interactions between plant nutrients. The sum of equivalents of cations in a soil solution is equal to the sum of soluble anions. Therefore, the amount of cations in a soil solution is maintained by a synergetic effect of anions. The relations between cations are determined by the relation between the exchangeable cations, according to a derived Gapon equation. An over-optimal concentration of a cation acts antagonistically to the effect of other cations on plant nutrient uptake. Sometimes the soil solution reactions are complicated, and antagonism between anions becomes obvious. When describing interactions between plant nutrients by synergism and antagonism, it is valuable to develop analytical methods to determine activities and concentrations in defined extracts of soils. The theory and procedure are described in this paper.