Nitrogen Use Efficiency Of Grain Crops Under Optimized Nitrogen Application And Manure Substitution In China

Nitrogen?N?plays an important role in agricultural production,and the chemical N fertilizer is the main source of N in farmland and the basis for ensuring crop yield.However,excessive application of N fertilizer often does not further increase the yield of crops,or even decrease,which leads to the lower nitrogen use efficiency?NUE?,and the larger nitrogen surplus?Nsur?in farmland,caused degradation of soil quality and environmental pollution.In this study,based on the national fertilizer efficiency experiment data?3414 experiment?,the optimal N application rate and the corresponding yield,NUE and Nsur were estimated in all regions of China;Based on data collected from literature,the effects of manure substitution on crop yield and NUE were analyzed.The main results are as follows:1.Under the condition of high yield,the recommended N application for wheat,maize and rice were150?197,171?195 and 136?187 kg hm^-2 in China,and the average yield can reach 5993,8847 and8002 kg hm^-2,the NUE were 70%,59%and 75%,respectively.The Nsur of wheat and rice in each region is below 80 kg hm^-2,the Nsur of maize is below 80 kg hm^-2 in Northeast,and about 110 kg hm^-2 in North China Plain and Southwest,88 kg hm^-2 in Northwest.Compared with the current farmers'conventional N application,the total N reduction can reach 3×10⁶ t,harvest 1.7×10⁹$of economic benefits.2.Compared with NPK,NPKM treatment average increased the yield by 5.7%,and the yield increase rate of wheat,corn and rice was 5.6%,7.6%and 4.5%,respectively.The improvement of yield by manure application varied among regions:Northwestern China>Northeast,North China>Southern Region>Eastern China.The increment of yield by manure application was higher in the soils with lower organic matter and total nitrogen content than that in the soils with high organic matter and total nitrogen content.The increase of yield in alkaline soils?pH>7.5?with manure applied was 1.4%and 2.4%higher than those in acidic?pH?6.5?and neutral soils?6.5<pH?7.5?,respectively.The highest enhancement of yield by manure application was found at temperate continental climate zone,followed by temperate monsoon climate zone,subtropical monsoon climate zone.3.Compared with NPK,NPKM treatment increased the NUE by 3.6%.NPKM treatment significantly increased the NUE of crops in all regions except the Northeast China.The highest enhancement was found at Northwestern China,followed by Northern China,Southern Region and Eastern China.The increment of NUE by manure application was higher in the soils with lower organic matter content than that in the soils with high organic matter content.The increase of NUE in alkaline soils with manure applied was 1.3 and 1.8 times higher than those on neutral and acidic soils,respectively.The improvement of NUE by manure application varied among climate regions:temperate continental climate zone>temperate monsoon climate zone>subtropical monsoon climate zone.In summary,by optimizing the N application rate to three main food crops in China,the application of chemical N fertilizer can be reduced on the basis of ensuring crop yield,the NUE can be improved,and the Nsur can be reduced;Manure substitution could significantly increase the yield and NUE of crops,especially in northwestern areas with low organic matter content and less rainfall.