稻鱼共作下氮肥减量后移对水稻生长和氮肥利用效率的影响

为了探索稻鱼模式下水稻氮肥高效施用技术，实现减肥增效的生产目标，以杂交籼稻隆两优1206为试验材料，在稻鱼共作模式下设置了4个水稻施氮处理，分别为：N0不施氮肥处理、CK当地常规施氮处理(纯氮用量为 180 kg/hm²，按分蘖肥∶促花肥∶保花肥=5∶2.5∶2.5施用)、N1氮肥减量处理(纯氮用量为 120 kg/hm²，按分蘖肥∶促花肥∶保花肥=5∶2.5∶2.5施用)、N2氮肥减量后移处理(纯氮用量为 120 kg/hm²，按分蘖肥∶促花肥∶保花肥=0∶5∶5施用)，研究了不同处理下水稻生长特性、产量和氮肥利用率的变化规律。结果表明：与CK处理相比，N2处理显著降低了有效分蘖叶龄期水稻的分蘖数和倒4叶期水稻的干物质积累量，但在有效分蘖叶龄期的分蘖数达到了CK处理有效穗数的88.54%，已经够苗。施穗肥后N2处理增加了水稻的干物质积累量、有效穗数和穗粒数，同时显著降低了水稻的高峰苗，提高了成穗率，两年的水稻产量比CK处理分别增加了6.39% 和8.57%。同时，N2处理降低了水稻成熟期土壤水解氮的残留，水稻氮素收获指数、氮素干物质生产效率、氮素谷物生产效率、氮肥偏生产力和氮肥农学利用率分别比CK处理提高了5.63%、12.99 kg/kg、12.91 kg/kg、28.45 kg/kg和7.79 kg/kg，增幅分别达9.33%、15.56%、29.14%、59.57% 和120.77%，差异均达到显著水平。可见，水稻氮肥减量后移施用，能够显著降低水稻高峰苗，提高水稻成穗率、后期干物质含量、有效穗数、穗粒数和氮肥农学利用效率，从而提高产量。在西南地区烟后稻田养鱼模式下，茬口土壤全氮和水解氮分别在1.79 g/kg和160.02 mg/kg以上，水稻采用总施氮为 120 kg/hm²，按分蘖肥∶促花肥∶保花肥=0∶5∶5比例的施用，可以实现水稻减氮33.3%、增产6.39% 以上的目标。

Effects of Postponing and Decreasing Nitrogen Fertilizer on Rice Growth and Nitrogen Use Efficiency Under Rice-fish Coculture

In order to explore nitrogen (N) high-efficiency application technology of rice under rice-fish coculture and achieve the goal of N reduction and efficiency increase, a field plot experiment was conducted under rice-fish coculture with Longliangyou 1206 as planting material, in which four different N application treatments of rice were designed, 1) N0: no N application; 2) CK: local conventional N application, 180 kg/hm², 50% topdressing at 15d after transplanting, 25% and 25% topdressing at 4^th and 2^nd leaves emerged from the top, respectively; 3) N1: reducing N application, 120 kg/hm², 50% topdressing at 15d after transplanting, 25% and 25% topdressing at 4^th and 2^nd leaves emerged from the top, respectively; 4) N2: reducing and postponing N application, 120 kg/hm², 50% and 50% topdressing at 4^th and 2^nd leaves emerged from the top, respectively. Rice growth characteristics, N use efficiency, yield and yield components were measured. Results show that N2 treatment significantly reduces the number of tillers at the critical leaf age for productive tillers and the dry matter accumulation of rice at the inverse 4^th leaf stage, but the number of tillers at the critical leaf age for productive tillers reaches more than 88.54% of the effective panicles of the CK treatmenmt, which is enough for tillers. The application of panicle N fertilizer increases the dry matter accumulation, effective panicles and number of grains per panicle under N2 treatment, and significantly reduces the peak seedling of rice and improves the spike rate. The rice yields in the two years are increased by 6.39% and 8.57% respectively, compared with the CK treatment. At the same time, the N2 treatmenmt reduces the residue of hydrolysable N in soil at rice maturity stage, and N harvest index, N use efficiency for biomass production, N use efficiency for grain production, partial factor productivity of applied N and N agronomy efficiency are 5.63%, 12.99 kg/kg, 12.91 kg/kg, 28.45 kg/kg and 7.79 kg/kg higher than the CK treatment (P<0.05), increased by 9.33%, 15.56%, 29.14%, 59.57% and 120.77%, respectively. In conclusion, the postponing and decreasing N fertilizer in rice could significantly reduce the peak seedling of rice and improve the spike rate, the dry matter accumulation, effective panicles, number of grains per panicle, N agronomy efficiency and yield. Under the rice-fish coculture mode after tobacco in southwest China, the total N and hydrolyzed N in soil are more than 1.79 g/kg and 160.02 mg/kg respectively, and the total N are 120 kg/hm², and the application ratio is 50% topdressing at 4^th and 2^nd leaves emerged from the top respectively, which could achieve the goal of reducing N fertilization by 33.3% but increasing rice yield by more than 6.39%.