Model studies on salt and water balances at Konanki pilot area, Andhra Pradesh, India

The salt and water balances at Konanki pilot area in Nagarjunasagar project right canal command in Andhra Pradesh State of India were analysed using SALTMOD. The model was calibrated by using two-year data collected in the pilot area. From the calibration, the leaching efficiencies of the root and transition zone were estimated as 65% and the out going natural sub-surface drainage was determined as 50 mm per year. The model predicts that the root zone soil water salinity will be reduced to 4, 3 and 2.5 dS/m (from an initial value of 11.5 dS/m) during the first, second and third seasons within six years after installation of the drainage system. Next, the situation prior to the installation of the drainage system was reconstructed using the model. Finally, sensitivity analyses were made to study the effects of varying drain depth, spacing and amount of irrigation water applied on root zone salinity and depth to water table. Here, the model predicted that closer than the present spacing or further deepening of the drains from the present depth of 1 m to 1.4 m will not have any better influence on the reduction of the root zone salinity than in the present situation. These simulations also suggested that by applying 80% of the present amount of irrigation water, the root zone salinity can be brought down to 5 and 4 dS/m by second and fourth years, respectively and this will in turn reduce the problem of water logging and salinity to some extent.