| Nitrogen（N）is one of the most important factors affecting the winter wheat yield.Reasonable N fertilizer application rate is the fundamental way to achieve high yield,high fertilizer use efficiency in wheat production in drylands.The determination of soil nitrogen supply capacity is the premise of the recommended application rate of N fertilizer,and the level of soil N supply capacity mainly depends on the content of soil organic matter（SOM）.Therefore,it is possible to recommend the application N fertilizer rate based on the content of soil organic matter.This study collected literatural data on the impacts of soil organic mater mineralization and long-term fertilization on the content of soil organic matter,and did surveys in Weibei dryland of Shaanxi province.A recommended N fertilizer application method that based on the soil organic matter content was proposed.From 2014 to 2017,a field experiment was conducted to verify this recommended method in six counties of winter wheat planting area in Weibei dryland and reveal the effects of the recommended fertilization method on wheat yield,nutrient utilization efficiency,soil nitrate N residue and economic benefits,and it aimed to provide a method for rational N fertilization in dryland wheat production.The main findings are as follows:（1）A meta-analysis was used to summarize the effects of long-term localized fertilization on organic matter content and found that the content of SOM in treatment with long-term non-fertilization decreased by 4.3%while long-term fertilization treatments increased the content of SOM.Compared to the values of SOM before the experiment,SOM in M,NPKM and NPKS treatments were increased by 44.8%,44.1%and 29.2%,respectively.While,in the single application of chemical fertilizer treatment,the N,P,NP and NPK treatments significantly increased SOM by 3.6%,3.9%,6.8%and 13.0%,respectively.These results showed that organic fertilizer and balanced NPK fertilizer application can improve the content of SOM.In addition,the change of SOM in long-term investment of organic matter for 20 years is slow or close to saturation,indicating that the input of organic fertilizer can be appropriately reduced to save resources.（2）The analysis of the literature data found that the soil organic matter content was significantly and linearly related to the annual soil organic matter mineralization and soil total nitrogen content,i.e.,for every 1 g kg-1 increase in soil organic matter,the annual mineralization of soil can increase by 3.70 kg ha-1.The survey data showed that the residue of nitrate N in the 0-to 1 m soil layer at harvest increased gradually with the increase of organic matter content in the surface soil,i.e.,the residue of nitrate N increased from 92 to164 kg ha-1 when SOM increased from less 10 g kg-1 to more than 17 g kg-1,which suggeseted that the content of SOM could represent the soil N supply capacity and could be used as an index of N supply capacity for the recommended application of N fertilizer.（3）The results of the field experiment in Weibei dryland for three years showed that the average application rates of N,P and K fertilziers in farmers’fertilization（FP）treatment were 190,120 and 34 kg ha-1,respectively.However,the values in the recommended fertilization method that based on SOM（OFP）were 161,71 and 31 kg ha-1,respectively,with decreases of 15.3%,40.8%and 8.8%,respectively.Compared with thr FP treatment,the average yield and biomass of OFP treatment were 5817 and 13419 kg hm-2,respectively,which were 9.0%and 11.0%higher than those of FP treatment(5337 and 12086 kg hm-2).The average number of spikes and 1000-grain weight of OFP treatment was 5.11 million spikes ha-1 and 39.1 g,respectively,with an significant increase of 6.7%and 2.9%.These results indicated that OFP treatment can effectively reduce the amount of N fertilizer input and increase the yield of winter wheat.（4）The average productivity of N,P,K fertilizer in the OFP treatment was 37.0,84.0and 190.1 kg kg-1,respectively,which were significantly higher than those in the FP treatment,with the increase of 30.3%,84.2%and 29.0%,respectively.Compared with FP treatment,the OFP treatment increased the economic benefits by 1460 yuan ha-1 of(7498vs 8949 yuan ha-1),while significantly decreased nitrate N residue in the 0-to 1 m soil layer at harvest by 28.3%(138 vs 99 kg ha-1),which suggested that the OFP treatment not only improved fertilizer utilization efficiency and economic efficiency,but also significantly reduced nitrate N residue in soil layer.In summary,the level of SOM content can effectively characterize soil N supply capacity,and can be used as a recommendation method for nitrogen fertilizer supply.However,in order to maintain or increase SOM content,the input of N,P,K,and even organic fertilizer should be balanced.The recommended N fertilization method that based on soil organic matter can decrease N fertilizer input and increase wheat grain yield,biomass and economic benefits,and also reduce the environmental risk.Therefore,this method could be used as a method of N fertilizer application for winter wheat production in Weibei dryland. |
