Grain yield, water and nitrogen use efficiencies of rice as influenced by irrigation regimes and their interaction with nitrogen rates

A major challenge in rice production is to achieve the goal of increasing both food production and resource use efficiency. This study investigated if and how irrigation regimes could synergisticly interact with nitrogen (N) rates to increse grain yield, water use effciency (WUE) and N use effciency (NUE) in rice. A field experiment was conducted with three N rates, 100 (low amount, LN), 200 (normal amount, NN) and 300 kg ha⁻¹ (high amount, HN), and three irrigation regimes, alternate wetting and moderate drying (AWMD), alternate wetting and severe drying (AWSD) and continuously flooded (CF). Among the three N rates, both grain yield and WUE were the lowest at LN in all the irrigation regimes, were the highest at NN in the CF regime and at HN in the AWSD regime, and showed no significant difference between NN and HN in the AWMD regime. Either internal N use efficiency or N partial factor productivity (PFP_N) decreased with the increase of N rates. At the same N rate, the AWMD regime showed the highest grain yield, WUE and PFP_N among the three irrigation regimes. Reduced unproductive tillers, enhanced root growth and increased harvest index contributed to a higher grain yield and higher resource use efficiency in the AWMD regime, especially at NN. The results indicate that adoption of an AWMD regime with an appropriate N rate can achieve a higher grian yield, WUE and NUE, and an increase in N rate can reduce the yield loss in an AWSD regime.