Modelling the Effects of Deficit Irrigation on Soil Salinity, Depth to Water Table and Transpiration in Semi-arid Zones with Monsoonal Rains

Abstract

A soil water and solute transport model, calibrated for a dominant soil series in the Punjab of Pakistan, was used to evaluate consequences of deficit irrigation in semi-arid areas with a shallow water table. Simulations were carried out to determine the influence of irrigation amounts and subsurface drainage conditions on root zone salinity, depth to water table and transpiration. Additional simulations were made to evaluate a range of irrigation practices adopted by farmers under field conditions. The simulation results show that provision of 80% of the cumulative evapotranspiration requirements as irrigation will result in acceptable limits of root zone salinity and depth to water table, without significantly affecting transpiration of wheat and cotton crops. Under such circumstances, subsurface drainage will not be necessary. Results also show that current irrigation practices in the Punjab are resulting in yield reductions in general, due to either water shortage or waterlogging.