Effects Of Long-term Optimal Fertilization On Soil Fertility And Nutrients In Dryland

Fertilization is one of the important measures to maintain high crop yields.However,blind fertilization is not only hard to maintain high crop yields,but also affects soil nutrient balance,reduces economic benefits,and poses a threat to the environment.Scientific optimization of fertilization must not only maintain high crop yields and increase nutrient use efficiency,but also ensure soil nutrient balance or without pose a threat to the environment.During 2014-2017,four field experiments were conducted in four counties of Weibei dryland in Shaanxi Province to determine the effects of different fertilization metods on wheat grain yield,nutrient use efficiency and soil fertility.The field treatments included:1)conventional fertilization（CFA）,2)optimized fertilization based on the soil nitrate-N,available P and K tests,crop nutrient requirements and the safety threshold of nitrate during harvest（OFA_N）,and3)optimized fertilization based on soil organic matter,available P and K content and crop nutrient requirements(OFA_OM).The main results are as follows:（1）Optimized fertilization(OFA_N and OFA_OM)not only decreased fertilizer application rates but also increased the grain yield,fertilizer partial productivity and economic benefit.According to the survey in 2017,96%of farmers overused nitrogen fertilizer,64%of farmers overused phosphorus fertilizer and 85%of farmers applied insufficient potassium fertilizer.Compared with conventional fertilization（CFA）,optimized fertilization OFA_N saved 27.3%of nitrogen and 40.8%of phosphorus fertilizers,and increased winter wheat grain yield by2.6%.Optimize fertilization OFA_OM saved 11.4%of nitrogen and 40.8%of phosphorus fertilizers.Compared with CFA,the partial productivity of nitrogen and phosphorus fertilizer increased by 15 kg/kg and 33 kg/kg,respectively.The economic benefits of two optimized fertilization methods were also increased by 514 yuan/hm²（OFA_N）and 1169 yuan/hm²(OFA_OM).（2）Optimized fertilization(OFA_N and OFA_OM)reduced the soil nitrate nitrogen residues in the soils,and thus reduced the environmental risks.Compared with CFA,the optimum fertilization of OFA_N and OFA_OM both reduced the amount of nitrogen fertilizer,and thus decreased the nitrate nitrogen accumulatation in the 1m soil layer,with the derease of 123kg/hm²（by 63.8%）and 86 kg/hm²（by 44.3%）respectively.The content of available phosphorus in 0-40 cm soil was 11.6-13.6 mg/kg while the available potassium was147.2-152.0 mg/kg in the two optimized fertilization treatments.In conclusion,the optimization of fertilization based on the nitrate-nitrogen test and soil organic matter can increase economic efficiency,reduce the nitrate-nitrogen residues in the soil and maintain the soil nutrient balance in dryland farming areas.Taking into account the environmental risk and economic benifits,the optimization of fertilization based on the nitrate-nitrogen test（OFA_N）should be recommended in the dryland of Shaanxi Province.