Alternate wetting and drying irrigation combined with the proportion of polymer-coated urea and conventional urea rates increases grain yield, water and nitrogen use efficiencies in rice

Interaction between water and nitrogen (N) plays important roles in regulating crop yields and resource use efficiencies. Little is known, however, if and how irrigation regimes could synergistically interact with proportions of polymer-coated urea (PCU) and conventional urea (CU) rates to increase grain yield, water use efficiency (WUE) and N use efficiency (NUE) in rice. This study investigated the question. Field experiments were conducted with three N treatments, 100 % CU (N1), 100 % PCU (N2), and 70 % PCU + 30 % CU (N3), and two irrigation regimes, continuously flooded (CF) and alternate wetting and moderate drying irrigation (AWMD). The results showed that grain yield, internal N use efficiency, N partial factor productivity, and WUE exhibited small differences among the three N treatments in the CF regime, whereas they were the highest under N3, and the lowest under N1 in the AWMD regime. The above parameters were the highest under the N3 + AWMD among the all treatment combinations. Enhanced root and shoot growth, especially increases in root oxidation activity, leaf area duration, crop growth rate, and photosynthetic NUE, and increased N uptake, pre-stored carbon remobilization from stems during grain filling, and harvest index at maturity, and higher nitrate-N content in the soil accounted for a better synergistic interaction under the N3 + AWMD treatment. Collectively, adoption of an AWMD regime with an appropriate proportion of PCU and CU rates (70 % PCU + 30 % CU) can synergistically increase grain yield and resource use efficiency by improving biological process in rice.