Optimization Of Nitrogen And Phosphorus Management For Dryland Wheat Based On Long-term Location-field Experiment

Winter wheat is the main food crop,and large amounts of nitrogen?N?and phosphorus?P?have accumulated in soil due to long-term over fertilization,and this has decreased fertilizer use efficiency and led to a series of environmental problems in Loess Plateau.In order to optimize the N and P fertilizer management based on soil N and P supply capacity,and with the purpose to increase the wheat grain yield and nutritional quality,a 13-year-long location-fixed field experiment was conducted on Weibei dryland in Shaanxi Province from2004 to 2017 to clarify the relationship among N and P fertilization rates to soil N,P and K nutrients,wheat yield,and grain N,P and K nutrient contents.Based on samples collected during 2015-2017,main results are as follows:1.Long-term N fertilizer input increased the winter wheat yield by 67.1%,biomass by52.0%and harvest index by 9.5%;It also increased the spike number and grain number per spike by 32.5%and 40.0%,respectively.while the thousand-grain weight decreased by 7.1%.With the N application rate increasing,the wheat yield and aboveground biomass were increased quadratically,the highest yield was 6587 kg hm^-2 with N application rate at 215 kg N hm^-2.2.The grain N content increased with the increase of N application rate,and compared with no N input,N application increased grain N content by 56.2%,decreased grain P content by 24.9%,and had no significantly influence on grain potassium?K?content.Nitrogen harvest index,N physiological efficiency,N partial productivity,and N agronomic efficiency decreased with the increase of N application rate.For each 100 kg of N hm^-2 increment,the N requirement for grain yield formation increased by 0.5 kg 100 kg^-1,P requirement decreased by 0.03 kg 100 kg^-1,and potassium requirement showed no significant change.3.With the N application rate increasing,the soil nitrate N content increased and the available P decreased,the soil available potassium had no significantly change.When the wheat yield reached at 6300 kg hm^-2,95%of the maximum yield,the soil nitrate N content were 6.0 mg kg^-1 and 8.0 mg kg^-1,soil available P were 12.0 mg kg^-1 and 15.0 mg kg^-1,and average soil available potassium was 140 mg kg^-1 at sowing and maturity,respectively.Corresponding,the N application rate was 150 kg N hm^-2,and P application rate was 100 kg P₂O₅ hm^-2.4.Long-term P application increased wheat yield by 67.2%,aboveground biomass by58.1%,spike number by 64.1%,kernel number by 8.0%and 1000-grain weight by 7.1%.Thewheat yield and aboveground biomass were increased quadratically with the P application rate increasing,the highest grain yield was 6465 kg hm^-2 at P application rate of 144 kg P₂O₅ hm^-2.5.The grain N content decreased with the increase of P application rate,compared with no P application,P application decreased grain N content by 6.6%,the grian P and K contents increased with the increase of P application rate,which was increased by 37.1%and 8.4%,respectively.The P absorption and utilization efficiency decreased with the increasing of P application rate.For each 100 kg of P₂O₅ hm^-2 increment,the P requirement increased by 0.7g100kg^-1 for the grain yield formation,the P harvest index decreased by 2.6%,and the wheat physiological efficiency decreased by 90.2 kg kg^-1.6.The soil available P content was significantly positively correlated with the application rate of P,soil nitrate N content decreased with the rate of P increased,and the available K did not change significantly.When wheat achieve the yield of 6141 kg hm^-2,95%of the maximum yield,available P were 12.0 mg kg^-1 at sowing and 13.8 mg kg^-1 at harvest,and the nitrate N were 7.0 and 8.6 mg kg^-1,and available K were 141 and 140 mg kg^-1,correspondingly,simutaneously the P application rate was 94 kg P₂O₅ hm^-2,and the N application rate was 160 kg N hm^-2.7.In conclusion,the target grain yield should be 95%of the maximum yield,6100-6300kg hm^-2 in drylands as the south of Loess Plateau,the N application rate should be kept at150-160 kg N hm^-2,the P application rate at 95-100 kg P₂O₅ hm^-2,and no potassium fertilizer were suggested to apply,when the soil nitrate N at sowing or harvest was 6.0-9.0 mg kg^-1,available P was 12.0-15.0 mg kg^-1,and available potassium was 140 mg kg^-1 correspondingly.For the long-term and sustainable application of N and P fertilizers,we should comprehensively consider the grain yield,key nutrient content and nutrient absorption and utilization of winter wheat,and optimize the N and P fertilizers application rates based on the soil nutrient supply capacity and the nutrient requirement of high yield and high quality in the green production of dryland wheat.