Effects of Nitrogen Topdressing Rates on Yield and Nitrogen Uptake and Utilization of Winter Wheat under Long-Term Straw Returning
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.
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