Abstract: 【Objective】In order to provide a scientific basis for high water-fertilizer use efficiency of rice, the objective of this experiment was to study the effects of water and nitrogen (N) management patterns on population quality and yield of hybrid rice.【Method】Gangyou 527, an elite indica threeline hybrid rice cultivar widely planted in rice production in China, was used, which has high grain yield, extensive adaptability, and pest-resistance with growth duration of 145-150 days from sowing to maturity. The experiment was conducted to optimize N application, understand how different combinations of water and N management affect population quality of hybrid rice and yield, and study the correlations of population quality index and grain yield. Three irrigation regimes including submerged irrigation (W1), controlled alternate irrigation (W2), and dry cultivation (W3) combined with four N application managements at 180 kg?hm-2 of total N conditions were designed in the study. The four N application ratios were applied on different splits: (a) 2 splits: 70% basal and 30% 7 d after transplanting (DAT) (N1), (b) 3 splits: 50% basal, 30% 7 DAT, and 20% panicle N-fertilizer according to different leaf ages when 4th leaves emerged from the top (N2), (c) 4 splits: 30% basal, 30% 7 DAT, 40% panicle N-fertilizer equally when 4th and 2nd leaves emerged from the top (N3), (d) 4 splits: 20% basal, 20% 7 DAT, 60% panicle N-fertilizer equally when 4th and 2nd leaves emerged from the top (N4), in addition, no N application (N0) was designed as control. 【Result】 The results showed that there was an obvious interaction between irrigation regime and N application on dry matter accumulation and leaf area index (LAI) at the mainly growth stages, grain-leaf ratio at heading stage, net photosynthetic rate and yield. Decomposition analysis of water and nitrogen interaction effects showed that appropriate increase of N application ratio of later stage or W2 treatment had a positive effect on yield, the N application treatments had significant differences, and ranked as N3＞N2＞N1, and N4 treatment or W3 treatment resulted in a negative effect of water-nitrogen interaction. Compared to irrigation regimes, the results of water and nitrogen interaction showed that W2 treatment promoted the efficiency of N fertilizer, and achieved the purpose of promoted fertilizer by water. W2 treatment with suitable treatment of N3 application (30% basal, 30% tillering, 40% panicle N-fertilizer equally at 4th and 2nd leaves emerged from the top) was the best model in this paper and referred as the water-nitrogen coupling model, which could control the number of rice tillering, improve the rate of tiller panicle, guarantee the appropriate LAI and grain-leaf ratio at filling stage, increase the efficient leaf area ratio and population light transmission rate, and thus improving photosynthetic capacity at filling stage and the accumulation of photosynthetic products, and on the premise of effective panicle and seed-setting rate, the yield increased significantly. However, the other combinations of irrigation regimes and N application managements resulted in weakened advantages, or even resulted in the negative effects of water-nitrogen interaction and decreased of grain yield. Especially, either W3 treatment or high N application ratio of later stage (N4 treatment) resulted in yield reduction, and aggravated negative effect of water-nitrogen interaction. According to yield performance under W3, the proper decrement of panicle N-fertilize ratios could ease the negative effect of water-nitrogen interaction to some extents, and suitable panicle N-fertilizer should account for 20%-40%. Under W1, however, on the basis of 40%-60% base tillering N fertilizer, panicle N-fertilizer should account for 40%-60%. Correlation analysis indicated that there existed significantly or highly significantly positive correlations (r=0.589*-0.978**) between index of population quality and yield under water-nitrogen interaction, especially had positive correlations between yield and increasing amount of dry matter at filling stage and decrement of population light transmission rate from full-heading stage to 20 days full-heading stage.【Conclusion】The results suggest that rice plant growth could be improved and high grain yield could be achieved through integrating and optimizing water-fertilizer regulating techniques in rice production. W2 and suitable N3 combined application was considered to be optimum under the experimental conditions, optimum N management pattern was also N3 for W1. However, under W3 treatment, the ratio of panicle N-fertilizer application should be decreased, and N management patterns (50% basal, 30% tillering, and 20% panicle N-fertilizer at 4th leaves emerged from the top) were considered to be optimum for W3.

Key words: hybrid rice, irrigation regimes, nitrogen application, population quality, yield