Modeling Moisture Flow in Root Zone: Identification of Soil Hydraulic and Root Water Uptake Parameters

Abstract

The present study is concerned with the analysis of moisture flow in the crop root zone and estimation of soil hydraulic and root water uptake parameters from soil moisture depletion data using the inverse procedure. The parameter estimation is formulated as a least-squares minimization problem in which the parameters are estimated by minimizing the deviations between model-predicted and field-observed soil moisture data in the root zone. A parameter estimation code is developed by coupling a numerical model simulating one-dimensional vertical moisture flow (Richards equation) in the root zone with a genetic algorithm. The root water uptake is accounted for as a sink term in the Richards equation. Identifiability of soil hydraulic and root water uptake parameters from the inverse procedure are studied by generating synthetic soil moisture depletion data. It is observed that with soil moisture data alone, it is not possible to estimate both soil hydraulic and root water uptake parameters uniquely. This is evidenced by the presence of local minima in the parametric space involving root water uptake as one of the parameters. Field experiments were also conducted on two major Indian crops: wheat and berseem. The inverse procedure is applied to estimate the root water uptake parameter for these crops. Using optimized values of root water uptake parameter of the two crops, the percentage soil moisture depletion at discrete irrigation intervals are compared with observed data. The results indicate a fair agreement between the computed and observed percentage soil moisture depletion values.