A Steady‐State Model of Nutrient Uptake Accounting for Newly Grown Roots

Abstract A model of solute uptake that accepts root growth, water uptake, and soil solution concentration as time‐varying input is required to interactively link plant and soil processes. The advantage of the steady‐state approach to solute uptake over more exact numerical solutions lies in the independence of the mathematical solution to previous conditions. Uptake thus calculated can accommodate unpredictable changes in root growth and mortality, root density, water uptake rates, and sources and sinks of nutrients such as decomposition and leaching, as required in simulating plant growth for multiple seasons in a dynamic soil environment. Previous steady‐state models were improved by including nonlinear uptake kinetics and the contribution of new root growth to uptake. The correction for new root growth is most important for relatively fast‐growing plants and immobile nutrients. The importance of each model parameter, as indicated by sensitivity analysis, depends on the values of other parameters. For example, root surface area and uptake kinetics are important when solution concentrations at the root surface are high, while root length, water uptake rate, and diffusion become important when delivery of solute to the root surface is limiting. Because the limiting factors can vary with environmental and plant conditions, it is important to represent these aspects of nutrient uptake in modeling plant‐soil interactions. A consistent derivation of the improvements and the original model is appended.