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Modelling the contribution of root accessible water tables towards crop water requirements

Proper utilization of shallow water tables could substantially reduce irrigation water requirements in large agricultural areas. The objective was to develop and test a computer model for predicting the contribution of shallow water tables to root water uptake. The model uses a finite difference solution of the Richards' continuity equation, based on thermodynamic principles of water flow, to determine equilibrium conditions of matric potential in the soil profile. The model was tested using data from a lysimeter trial in Bloemfontein (South Africa). The field trial was carried out for different crops (maize, wheat, groundnuts and peas) and soils (sandy and sandy loam) by artificially keeping the water table depths constant (1 and 1.5 m) in lysimeter containers. The finite difference water redistribution model predicted crop growth, volumetric soil water content as well as the contribution of water tables to crop water uptake well, provided the soil hydraulic properties used as inputs were calibrated.