Effects of irrigation and nitrogen management on nitrogen use efficiency and yield of hybrid rice cultivated in ditches under no-tillage

【Objectives】 Rice planting in ditches under no-tillage are widely extended in Sichuan Province. Studying the effects of different water and nitrogen managements on the dry matter accumulation, transport and nitrogen use efficiency could provide a basis for efficient water and fertilizer use in rice production. 【Methods】A two-factor split-plot design field experiment was conducted with hybrid rice cultivar F-you 498 as material. The main plot was two irrigation modes: floodingirrigarion (W1) and alternating wet-dry irrigation (W2); The subplot was three N application ratios in total amount of 150 kg/hm2, the ratio of basal ∶ tillering ∶ panicle were 6 ∶2 ∶2, 4 ∶2 ∶4 and 2 ∶2 ∶6, no N application (N0) was set as control. Biomass and nitrogen accumulation, biomass transportation in stems and sheaths, and N utilization on full heading stage, after full heading stage 20 days and maturation stage were studied. 【Results】 Alternating wet-dry irrigation benefits the formation of expanded “reservoir” and “source”, which in turn ensure adequate spikes and high biomass accumulation. Flooding irrigation resultes in more ineffective tillers and poor population quality, thus adversely affects biomass accumulation, N uptake and yield formation. Postponing nitrogen fertilization provides more balanced N supply in the whole growing period, which promotes the total absorption and accumulation of nitrogen. The highest apparent N use efficiency rate is 69% in N2 treatment, in which the partial actor productivity of nitrogen, the N agronomic efficiency, the N apparent use efficiency and the yield are 4.50%-36.85%, 8.09%-28.54% and 7.47%-15.76% higher than those of N1(6 ∶2 ∶2) and N3(2 ∶2 ∶6). Rational management of water and nitrogen increase the nitrogen accumulated at each growth stage significantly. 【Conclusions】 Alternating wet-dry irrigation in combination with N application ratio of 4 ∶2 ∶4 in basal ∶tillering ∶panicle is the optimal water and nitrogen management in the tested cultivation condition. The water and nitrogen management has significant coupling effect in promoting the formation of large nutrient source and effective transfer to the “reservoir” after full heading stage, which is in favor of buildup of high yield, and N use efficiency.