Mechanistic simulation models of nutrient uptake: A review

Abstract

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 describing changes in root geometry and size due to root growth and others describing kinetics of the nutrient uptake process. Mechanistic models generally assume that nutrient uptake occurs evenly along the roots that are uniformly distributed in homogeneous and isotropic soil having no temporal and spatial gradients in volumetric moisture content. Uptake of immobile nutrients (like P and K) is mainly determined by the soil-supply parameters and is well predicted by the simulation models. In contrast, uptake of mobile nutrients (e.g. Ca and Mg) that usually accumulate at the root surface is determined mainly by the plant-uptake parameters; prediction of uptake of those nutrients is subject to a much wider error due to uncertainties of applying kinetic parameters measured on hydroponically-grown plants to soil-grown plants. Comparison of model-predicted and experimentally-observed uptake values should be done by calculating the mean squares of deviates instead of performing regression analysis, especially if data that encompass a relatively wide range in root length are considered. Complementaryion effects occurring at the soil-root interface raise the need for developing a multi-nutrient uptake model that will simultaneously calculate uptake of several essential nutrients taking into account interactions among them.

Nutrient uptake estimates for woody species as described by the NST 3.0, SSAND, and PCATS mechanistic nutrient uptake models

“…Usually, these models consist of three basic components (Rengel 1993): (i) solute movement in the soil toward plant roots described by the continuity equation …”

“…The soil is homogeneous and isotropic (Rengel 1993). water influx at the distance r 1 α root absorbing power θ volumetric soil moisture Nutrients move to the root by a combination of mass flow and diffusion .…”

“…Two general categories of nutrient uptake models, empirical and mechanistic models have been developed to study nutrient uptake by plant roots (Rengel 1993). Empirical models are based mainly on regressions as well as statistical means, often for practical use .…”

“…Empirical models are based mainly on regressions as well as statistical means, often for practical use . Mechanistic models, on the other hand, require an understanding of the mechanisms and a quantitative description of the phenomena (Rengel 1993). Mechanistic models are therefore useful to test the correctness of our knowledge of the phenomena .…”

“…represented by a set of equations that describe (Rengel 1993 Research on several crop species has demonstrated that the predictions of these mechanistic models generally match the observed uptake under situations in which the soil and plant conditions are relatively constant . However, results with woody species have been more variable .…”