Potential Of Returning Corn Straw To Replace Nitrogen Fertilizer And The Effect Of Reducing Fertilizer Application In Guanzhong Plain

In order to explore the potential of long-term straw returning mode to organically replace chemical nitrogen fertilizer and verify the application effect of monitoring fertilization method in wheat-maize rotation system,two field experiments were arranged in Guanzhong area.The first was a 10 consecutive years positioning experiment of straw returning and nitrogen fertilizer application in Zhouzhi County.The main treatments were corn straw returning（S+N）and without straw returning（N）,and the experiment plots were divided into five nitrogen application levels（N0,N84,N168,N252,N336 kg N/hm²）.The amount of nitrogen fertilizer that can replace the next crop of winter wheat by returning corn straw to the field was analyzed,and the effects of straw returning and different nitrogen application rates on the yield,nutrient absorption and soil fertility of winter wheat were analyzed.The second was to conduct a survey on fertilization of farmers in Wugong County（WG）,Fengxiang County（FX）and Fufeng County（FF）of Shaanxi Province.Evaluate the feasibility of monitoring fertilization according to the research results.Field comparison experiments were conducted in 3 counties to compare the wheat yield,nutrient absorption,economic and environmental benefits under the straw returning mode to monitor the fertilization mode（MF）compared with the farmer mode（CF）.The main conclusions reached are as follows:（1）Returning straw to the field increased the average yield of winter wheat by 2.1%,the interannual variation range was-0.8%～4.2%,and the variation range of different nitrogen application treatments was-3.7%～4.4%.The yield of winter wheat was reduced by straw returning without nitrogen（N0）,and the yield of winter wheat was the largest under N252treatment.Compared with N0,the treatment of straw returning with N84,N168,N252 and N336 increased the yield by 9.5%,17.3%,18.1%and 15.9%,respectively.Compared with no straw returning,the number of ears,grains per ear and 1000 grain weight of winter wheat increased by 6.1%,-0.9%and 0.5%respectively.The straw returning treatment had no significant effect on the yield and components.Nitrogen application treatment has a very significant effect on yield and 1000-grain weight,and has a significant effect on the number of ears per hectare and the number of grains per ear.The interaction between straw returning and nitrogen application did not have significant effect on yield and components.Among the three factors of yield,the number of ears per hectare had the highest correlation with yield.（2）There was no significant correlation between straw returning and grain protein content of winter wheat.Under the straw returning mode,the variation range of different nitrogen application treatments was 7.6%～18.9%.Among them,the grain protein content of N168,N252 and N336 treatment reached a significant level compared with N0 treatment.Compared with the treatment no straw returning,the nitrogen,phosphorus and potassium uptake of winter wheat were increased by 21.1%,18.1%and 10.2%respectively.With the increase of nitrogen application,the nitrogen and potassium uptake of winter wheat treated with straw returning showed an increasing trend.The variation ranges of different nitrogen application treatments were 17.1%～35.4%and 5.0%～30.1%respectively.（3）Straw returning to the field increases the residual amount of nitrate nitrogen in the soil profile of 0-200 cm,up to 87.6 kg/hm².The effect of straw returning on soil Olsen-P was low,and the average increase of Olsen-P in 0-20 cm soil layer was 2.7 mg/kg.The effect of straw returning on the content of available potassium in 0-20 cm soil reached a significant level,and the average increase of available potassium was 23.2 mg/kg.The soil organic matter of straw returning treatment increased by 5.6%,and the change of organic matter was less affected by the amount of nitrogen application,and had no correlation with the amount of straw returning in that year.（4）Calculated from the fertilizer effect curve of long-term positioning test,straw returning to the field with N168 can replace about 64.5 kg N/hm² of nitrogen fertilizer,and the average nitrogen fertilizer replacement of long-term corn straw returning to the field should be 49.4～85.6 kg N/hm².（5）In the wheat field of Guanzhong Plain,26.2%,29.0%and 11.2%of farmers apply nitrogen fertilizer,phosphorus fertilizer and potassium fertilizer reasonably,and less than one third of farmers apply chemical fertilizer reasonably.Fewer than one-third of farmers use chemical fertilizers properly.The field experiments in three counties in Shaanxi Province showed that:compared with the farmer model（CF）,Wugong County（WG）’s monitored fertilization（MF）decreased the total amount of chemical fertilizers by 17.6%,and the winter wheat yield increased by 3.8%.Compared with WG-CF,WG-MF increased the net income by866 yuan/hm²,and increased the production-to-investment ratio by 0.2,and decreased GHG emissions by 290 kg CO₂ eq Mg^-1.Fengxiang County（FX）MF decreased by 22.0%compared with the total amount of CF fertilizers,and the winter wheat yield increased by 5.0%.Compared with FX-CF,FX-MF increased the net income by 1296 yuan/hm²,increased the production-to-investment ratio by 0.3,and decreased GHG emissions by 416 kg CO₂ eq Mg^-1.Fufeng County（FX）MF decreased by 37.4%compared with the total amount of CF fertilizers,and the winter wheat yield increased by 6.8%.Compared with FX-CF,FX-MF increased the net income by 1778 yuan/hm²,increased the production-to-investment ratio by0.4,and decreased GHG emissions by 810 kg CO₂ eq Mg^-1.Monitoring fertilization reduces environmental risk compared with farmer mode.