Simulating nitrogen transport in paddy crop irrigated with alternate wetting and drying practice

Alternate wetting and drying (AWD) practice in rice cultivation can save a significant amount of irrigation water compared to conventional practice. This practice involves a soil moisture stress-based irrigation scheduling and possibly affects the nitrogen transport in the farm fields. In this study, non-weighing lysimeter plots were used to understand the nitrogen transformation, transport and balance of rice soil under AWD practice. The lysimeter data sets were used to simulate the nitrogen transport for no soil moisture stress (NS: 0 cm), mild soil moisture stress (MS: 450 cm) and severe soil moisture stress (SS: 700 cm)-based irrigation scheduling by using Hydrus-1D model. The Hydrus-1D model was able to simulate N transport (NH4+-N and NO3--N) from the ponding water to the soil-plant system for both calibration and validation datasets. The simulation results indicated that the applied N was mostly concentrated within the puddled (top) layer but slightly decreased with the increase in the soil moisture stress. The N crop uptake and leaching loss were decreased by 6% and 38%, in MS and by 15% and 52% in SS, respectively, when compared to NS (flooded rice). Both volatilization and denitrification losses were increased by 14 and 7% in MS, and by 17 and 7% in SS, respectively, when compared to NS. The Hydrus model can be used as a management tool to determine the appropriate soil moisture stress in the puddled layer for which the required N nutrients are sufficiently available to the rice crop and the N loss to the environment can be controlled.