Simulation and optimization of ponding water and nutrient management in rice irrigated with alternate wetting and drying practice under a humid subtropical region in India

Alternate wetting and drying (AWD) irrigation practice requires an appropriate threshold value for which, maximum water savings and minimum water and nutrient loss can be achieved without affecting the grain yield significantly. Determining the appropriate AWD threshold value experimentally is a challenging task. Mathematical models with optimization can be substitute tools for determining appropriate AWD threshold value. In this study, field studies were carried out using the non-weighing lysimeters with three levels of irrigation treatment (no soil water stress: NS, mild soil water stress/400 cm: MS and severe soil water stress/750 cm: SS) along with three levels of nitrogen application rate (high nitrogen: HN/150 kg/ha; medium nitrogen: MN/120 kg N/ha; low nitrogen: LN/60 kg N/ha). Each treatment was replicated three times. The field experimental data were used to determine the crop production function and simulate water flow and nutrient transport with the help of the Hydrus-1D model. Finally, the simulated results were optimized with the help of Design Expert software and appropriate irrigation (ponding water depth, soil matric potential head) and nutrient management (nutrient application rate) practice determined. The simulated results indicate that, the change in ponding water depth, soil matric potential head and nutrient application rates affect the water flow, nutrient transport and grain yield significantly. Overall, the 4.5 cm ponding water depth with the recommended dose of fertilizer (N: P: K-120: 50:60 kg/ha) and soil matric potential head of 400 cm was considered as an appropriate irrigation and nutrient management practice, which resulted a maximum grain yield of 5 t/ha and net profit of approx. Rs.20595.