Effects of irrigation method and straw mulch-nitrogen management pattern on straw decomposition characteristics and nitrogen utilization of hybrid rice

Irrigation methods have both direct effect and remote effect (through straw decomposition and nitrogen release especially when integrated with nitrogen management) on rice growth. A field experiment was conducted to evaluate the effect of irrigation methods and optimal straw mulch-nitrogen management pattern on root growth, nitrogen accumulation at main growth stages and grain yield of hybrid rice. Also straw decomposition and nitrogen release mechanisms were probed to clarify the effects of the interaction of straw decomposition and nitrogen release on rice growth. The results showed that flooding irrigation (W₀) and alternate wetting and drying irrigation (W₁) methods generally coordinated aboveground growth with underground growth, promoted nitrogen accumulation and increased grain yield compared with drought farming (W₂).However, the water productivity in W₂ treatment was the highest among all treatments, ollowed by W₁. For wheat and rape straw decomposition and nitrogen release, the peak values occurred 30 days after transplanting (30 DAT). However, the degree of decomposition and nitrogen release were influenced by both irrigation methods and straw types. The rape straw under W₂ treatment had larger degree of decomposition, while wheat straw under W₁ led to more nitrogen release. For straw mulch-nitrogen management patterns, wheat straw combined with optimal nitrogen management (S₁N₁) under W₀ and W₁ treatments efficiently coordinated the growth, promoted nitrogen absorption and eventually increased grain yield. However,rape straw combined with optimal nitrogen management (S₂N₁) had a slight inhibitory effect on the whole growth. Under drought irrigation, S1N1 and S2N1 had positive and remarkable effects on growth. Correlation coefficients showed that the effect of the degree of straw decomposition on the 30DAT was significantly negatively correlated with yield and nitrogen accumulation (r=-0.27^*to -0.29^*). Also the effect of the degree of nitrogen release at heading and ripening stages was strongly positively correlated with yield and nitrogen absorption (r=0.31^*to -0.59^**). Also the effects of the degrees of straw decomposition and nitrogen release on root and shoot growth was strong, especially for the heading stage (r=-0.27^*to -0.42^**). The results suggested that it was important for high grain yield and high efficiency of rice production to coordinate the straw decomposition and nitrogen release at different growth stages of rice, especially at 30 days after transplanting.