Abstract: The effects of nitrogen topdressing rates[0 kg/ha(N150),37.5 kg/ha(N150+37.5),75 kg/ha(N150+75),112.5 kg/ha(N150+112.5) and 150 kg/ha(N150+150)]on winter wheat population dynamics,accumulation and transport of dry aboveground matter and nitrogen,grain yield and nitrogen fertilizer utilization efficiency were studied under long⁃term straw returning and sufficient basal nitrogen application(150 kg/ha)to clarify the nitrogen topdressing rate for synergistically achieving higher grain yield and nitrogen fertilizer utilization efficiency,so as to provide theoretical basis and technical support for efficient nitrogen fertilizer management of winter wheat under straw returning.The results showed that with the increase of nitrogen topdressing rate,the number of tillers before winter and effective panicles showed a trend of first increasing and then decreasing,achieving higher values under treatments of N150+75 and N150+112.5.The aboveground dry matter and nitrogen accumulation before anthesis gradually increased with the increase of nitrogen topdressing rate,while the aboveground dry matter and nitrogen accumulation after anthesis followed a pattern of first increasing and then decreasing.The aboveground dry matter transport amount and rate before anthesis of treatments with no topdressing nitrogen(N150)and low topdressing nitrogen(N150+37.5，N150+75)were generally significantly higher than those with high topdressing nitrogen(N150+112.5,N150+150)and no nitrogen application(N0);The nitrogen transport amount before anthesis gradually increased with the increase of nitrogen application rate,reaching its maximum value under N150+150 treatment,but its nitrogen transport rate before anthesis was significantly lower than the other treatments.Compared with the treatment with only basal nitrogen of 150 kg/ha,topdressing nitrogen of 37.5—150 kg/ha at the jointing stage increased grain yield by 10.45%—33.64%.With the increase of nitrogen topdressing rate，the grain yield showed a pattern of first increasing and then decreasing，reaching its maximum value under N150+112.5 treatment,which significantly increased by 30.85%—33.64%,15.04%—20.99%,6.62%—11.07% and 7.35%—7.81% compared with N150，N150+37.5,N150+70 and N150+150 treatments respectively；Partial factor productivity，agronomic efficiency and physiological efficiency of applied nitrogen decreased linearly,and the difference between N150+75 and N150+112.5 treatments was not significant as a whole.In summary,topdressing nitrogen at the jointing stage is beneficial for increasing the accumulation and transport of dry matter and nitrogen of winter wheat before and after anthesis.However,excessive topdressing nitrogen leads to a significant decrease of transport rate of dry matter and nitrogen before and after anthesis,reduce the effect of yield increase,and significantly reduce nitrogen utilization efficiency. Under the condition of long⁃term straw returning and basal nitrogen of 150 kg/ha,nitrogen topdressing rate of 112.5 kg/ha at the jointing stage is conducive to the coordination of accumulation and transport of dry matter and nitrogen before and after anthesis.According to fitting analysis,nitrogen topdressing rate of 107.81—139.50 kg/ha at jointing stage can obtain high grain yield and nitrogen utilization efficiency.

Key words: Winter wheat, Straw returning, Nitrogen topdressing rate, Yield, Nitrogen uptake, Nitrogen utilization

摘要： 在长期秸秆还田且基施足量氮肥（150 kg/hm²）条件下研究拔节期不同追氮量［0 kg/hm²（N150）、37.5 kg/hm²（N150+37.5）、75 kg/hm²（N150+75）、112.5 kg/hm²（N150+112.5）和150 kg/hm²（N150+150）］对冬小麦群体动态、地上部干物质和氮素的积累转运、籽粒产量和氮肥利用效率的影响，明确协同实现较高籽粒产量和氮肥利用效率的追氮量，以期为秸秆还田下冬小麦氮肥高效管理提供理论依据和技术支撑。结果表明，随着施氮量的增加，冬小麦冬前分蘖数和有效穗数均呈先增加后降低的趋势，在N150+75和N150+112.5处理下较高。花前地上部干物质和氮素积累量均随施氮量的增加逐渐增加，花后地上部干物质和氮素积累量均呈先增加后降低的规律。不追氮（N150）和低追氮量（N150+37.5、N150+75）处理的花前干物质转运量与转运率总体上均显著高于高追氮量（N150+112.5、N150+150）和不施氮（N0）处理；花前氮素转运量随施氮量的增加逐渐增加，在N150+150处理达到最大值，但其花前氮素转运率显著低于其他处理。与仅基施氮150 kg/hm²处理相比，拔节期追氮37.5~150 kg/hm²增加籽粒产量10.45%~33.64%。随着追氮量的增加，籽粒产量呈先增加后降低的趋势，在N150+112.5处理下达到最大值，显著高于其他处理，分别较N150、N150+37.5、N150+75、N150+150 处理提高30.85%~33.64%、15.04%~20.99%、6.62%~11.07%、7.35%~7.81%；氮肥偏生产力、氮肥农学效率和氮肥生理利用率直线下降，N150+75与N150+112.5处理间差异总体上不显著。综上，拔节期追施氮肥有利于增加冬小麦花前、花后干物质和氮素的积累转运，但过量追氮导致花前干物质和氮素转运率大幅降低，产量增加效应减小，氮肥利用效率大幅降低；在长期秸秆还田基施氮150 kg/hm²条件下，拔节期追氮112.5 kg/hm2有利于协调冬小麦花前、花后干物质和氮素的积累转运，同时拟合分析发现，拔节期追氮107.81~139.50 kg/hm²可获得较高的籽粒产量和氮肥利用效率。

关键词: 冬小麦, 秸秆还田, 追氮量, 产量, 氮素吸收, 氮素利用