Optimum Sowing Date and Nitrogen Rate Ensure Sustainable Production of Wet Direct-Seeded Rice under Water-saving Irrigation Technique

Selection of an appropriate sowing date in combination with optimum nitrogen (N) rate and irrigation water management is important to optimize grain yield, water productivity, and N use efficiency (NUE) of wet direct-seeded rice (Oryza sativa L.). Field experiments were conducted during the dry rice growing seasons (November to March) of 2017–2108 and 2018–2019 to evaluate the interactive effect of sowing date (10, 20, and 30 November), N rate (0, 60, and 120 kg ha−1) and irrigation water management (alternate wetting and drying irrigation maintained at 15 cm threshold level [AWD] and continuous flooding) on growth, yield, total water productivity, and NUE of wet direct-seeded rice. The results revealed that the performance of plants sown on 10 and 20 November was statistically similar, but it was better than plants sown on 30 November in terms of growth, grain yield (22% increase), total water productivity (21% increase), and NUE (113% increase in agronomic efficiency and 38% increase in partial factor productivity). Moreover, N fertilization at 120 kg ha−1 maximized grain yield and total water productivity regardless of sowing dates and irrigation management practices, while AWD saved up to 45% of irrigation water input along with an 18% increase in grain yield when plants were fertilized with 120 kg N ha−1. Sowing dry-season rice early in November and fertilized with 120 kg N ha−1 under AWD irrigation has the potential to sustain productivity in the context of decreasing irrigation water availability for irrigated rice production systems.