Sensitivity of soil water content profiles in the root zone to extraction functions based on different root morphological parameters

Presented are results of simulations of root water uptake applying a macroscopic model of water transport in Soil - Plant - Atmosphere - Continuum. As a simulation tool is used the software package GLOBAL, based on the solution of the one-dimensional Richards equation. The main objective is to examine the contribution of root extraction functions (sink terms) based on different root morphological parameters to the changes in the soil water content profiles during the vegetation period of three crops. The root extraction functions are estimated using dry mass, length and surface area density distributions of all (total) and the fine roots (< 0.5 mm) of spring barley, winter rye and maize. It was observed that the "root mass" extraction curves slightly deviate from the "length" and "surface area" ones, especially in the topsoil and for the crops with a longer vegetation period. Nevertheless, the resulted differences in the soil water content distributions were small. The role of "fine roots" distribution was also examined. Calculating the water storage, it was found that the deviations were within the error of direct measurements. The sensitivity of the models based on the Richard's equation to the different root extraction functions was found to be low, which reflected in small differences in soil water content distributions. Hence, any of the studied root morphological parameters can be successfully applied for simulations of root uptake at macro scale.