MECHANISTIC SIMULATION-MODELS OF NUTRIENT-UPTAKE - A REVIEW

Mechanistic models of nutrient uptake consider diffusion and mass flow acting simultaneously to supply nutrients to the sorbing root surface . Plant parameters that determine nutrient uptake include those descri bing changes in root geometry and size due to root growth and others d escribing kinetics of the nutrient uptake process. Mechanistic models generally assume that nutrient uptake occurs evenly along the roots th at are uniformly distributed in homogeneous and isotropic soil having no temporal and spatial gradients in volumetric moisture content. Upta ke of immobile nutrients (like P and K) is mainly determined by the so il-supply parameters and is well predicted by the simulation models. I n contrast, uptake of mobile nutrients (e.g. Ca and Mg) that usually a ccumulate at the root surface is determined mainly by the plant-uptake parameters; prediction of uptake of those nutrients is subject to a m uch wider error due to uncertainties of applying kinetic parameters me asured on hydroponically-grown plants to soil-grown plants. Comparison of model-predicted and experimentally-observed uptake values should b e done by calculating the mean squares of deviates instead of performi ng regression analysis, especially if data that encompass a relatively wide range in root length are considered. Complementary-ion effects o ccurring at the soil-root interface raise the need for developing a mu lti-nutrient uptake model that will simultaneously calculate uptake of several essential nutrients taking into account interactions among th em.