ABSTRACT
Entry of nutrient elements into plants and, therefore, into the food web of human beings, depends on the capability of the soil to release and maintain a concentration bigger than the minimum concentration (cmin) of elements in the soil solution at the root surface, and on the uptake capacity of the plant roots. Root-induced rhizosphere processes influence nutrient availability, maintenance of the nutrient concentration in the soil solution and plant uptake. The entry into plants and the associated flux of a nutrient element toward root surface may be controlled by a number of rate-limiting and/or rate-determining processes. One of the rate-limiting processes may be the flux by diffusion from the solid constituents in the soil via the soil solution to the nutrient-absorbing cell membrane in root tissue near the root surface. The goal of good agronomy is always to obtain a useful and sustainable modification of rate-limiting and/or rate-determining processes in the soil plant atmosphere system, aiming at high yields and qualities of the crops. This goal requires identification of the rate-limiting and/or rate-determining steps, an understanding of their dynamics, and knowledge of how to obtain appropriate modifications of these steps.
