Improving nitrogen and water use efficiencies of hybrid rice through methodical nitrogen-water distribution management

Methodical nitrogen-water (N-W) distribution management (MNWD) is a comprehensive N-W management technique designed to meet the requirements of rice production in China and specifically, the stabilization of grain yield and reduction of input resources. In this study, four split plot field experiments were conducted in two locations to examine the impact of MNWD on N use efficiency (NUE) and water use efficiency (WUE). We used high N efficiency rice varieties, Dexiang 4103 and Fyou 498, and low N efficiency varieties, Yixiang 3724 and Chuanyou 6203, and three N-W management techniques were established as subplot treatments, including farmers' usual management (FU), N-W coupling management (NWC), and MNWD. Under MNWD, N application rates were 20% lower than those under NWC and FU, whereas the amounts of irrigation water were reduced by 20%-25% and 42%-48%, respectively. Yields under MNWD were similar to those under NWC (-2.51-0.45%), and there was an average yield increase of 8.13%-13.95% over FU. Rice plants under MNWD had larger amounts of roots, particularly in soil depth > 10 cm There were significant positive correlations between root dry mass in the various soil depths and WUE and irrigation WUE (IWUE), with the impact of roots in soil depth > 10 cm on rice plant WUE (IWUE) pronounced. MNWD's IWUE was higher than that of NWC and FU by 22.95%-38.79% and 86.49%-126.69%, respectively, and its WUE was higher by 6.75%-20.74% and 37.05%-71.80%, respectively. Correlation analysis showed that the N absorption and accumulation capacities of rice plants under MNWD increased along with increases in soil fertility. The MNWD's NUE advantage was apparent in soil depth > 10 cm where its root dry mass was especially large, with an average biomass productivity of N higher than that of NWC and FU by 4.16%-10.78% and 7.49%-18.01%, respectively and an N internal efficiency higher by 0.33%-8.29% and 5.32%-10.04%, respectively. Overall, MNWD effectively improved WUE and NUE of rice without significant grain yield reduction.