VADOSH ZONE MODELLING UNDER VARYING ENVIRONMENTAL CONDITION

Abstract

Irrigation water management can be carried out efficiently if the water demand of plants can be predicted precisely. In vadose zone modelling of cropped area, root water uptake functions are used to account for the sink term incorporated in Richards’ equation which is the governing differential equation for soil moisture movement in unsaturated porous media. In this study, a new water stress compensated nonlinear water uptake model has been proposed by incorporating water stress compensation mechanism (WCM) in an existing non-linear uptake model. Governing differential equation is solved numerically using the backward Euler finite difference approach and modified Picard’s iteration technique is used for linearization. A MATLAB code is developed to carry out the simulation. Observed data (including soil parameters and moisture data) for corn available in the literature is considered for moisture simulation. The performance of proposed model is compared with three other root water uptake models viz., non-linear uptake model and Lnrd uptake model with and without WCM. The soil moisture profiles simulated using four different uptake models are compared with the observed moisture values. The proposed model performs well in predicting the soil moisture profile with mean absolute error of 0.0167 and coefficient of variation 11.95% at 10 cm depth and mean absolute error of 0.0161 and coefficient of variation of 11.70% at 40 cm depth. In general, uptake models with WCM perform better than the original models. The performance of the proposed model is similar to the WCM incorporated Lnrd model while simulating moisture content at 10 cm depth. The proposed model simulates the soil moisture profile at 40 cm with least errors as compared to other models. This study also analyses the effect of considering water stress compensation mechanism on root water uptake patterns. A new methodology of considering diurnal variation of evapotranspiration is proposed which resembles the actual scenario. Inclusion of diurnal variation in the evapotranspiration is found to improve the model performances.