Optimized Fertilization For Cutting Down Fertilizers And Increasing Efficiency Of Wheat Production Based On Soil Test At Harvest And Regulating Fertilizer Placement In Dryland

Optimized fertilizer application is a critical way for high grain yield,high fertilizer use efficiency and friend realtion to environment and it plays a critical role in addressing the problems of over and imbalanced fertilization in wheat production systems.However,methods for optimizing fertilizer application are always complex due to variations in precipitation among years,seasons,and sites,as well as the unstable crop yields and nutrient requirements in dryland.In this study,in order to optimize fertilization for dryland wheat production,two optimized methods to determine the fertilizer rates were established based on soil test of nitrate residue?OFA_N?and organic matter(OFA_OM)at harvest of the previous crop and one optimized method to was developed to regulate fertilizer placement under plastic mulching cultivation?RFF?.Multi-site and fixed location field experiments were conducted from 2013 to 2016 with winter wheat?Triticum aestivum L.?as test crop to determine the effects of these methods on grain yield,economic return,nutrient absorption and utilization for nitrogen?N?,phosphorus?P?,and potassium?K?,soil water use and recharge,and soil nitrate residue in the typical dryland of the Loess Plateau in China.The major objectives of this study were to improve nutrient managements and facilitate sustainable crop production in dryland.The main results were as follows:?1?Optimized fertilizer application?OFA_N?mothed based on soil test of nitrate and available P and K at harvest,and crop nutrient requirements as well as the soil nitrate safety threshold decreased the fertilizer rates,and also balanced the relation of crop yield increase to high economic return,high nutrient use efficiency and environmental protection in dryland wheat production system.Compared with the conventional fertilizer application?CFA?,the OFA_N decreased the fertilizer application rates by 96 kg N hm^–2 and 43 kg P₂O₅ hm^–2,and the nitrate residues by 120 kg N hm^–2 in the 0¹00 cm soil layer,as well as increasing the wheat grain yield by 386 kg hm^–2 and the economic returns by 1472 Yuan hm^–2 averaged across three years and fifteen sites.Furthermore,the OFA_N method caused no changes in N,P and K uptake in wheat compared with CFA,but increased the harvest index,physiological efficiency for these nutrients and the partial factor productivity for the applied N,P and K fertilizer.?2?Optimized fertilizer application(OFA_OM)mothed based on testing soil organic matter and available P and K at harvest and crop nutrient requirements also decreased the fertilizer rates and facilitated the nutrient absorption and utilization in wheat plant.Therefore,the OFA_OM increased grain yield,economic returns,and nutrient use efficiency,reduced soil nitrate residue at harvest of wheat and simultaneously maintained nutrient balance in soil of dryland.Averaged across two years and twelve sites,the OFA_N decreased the N rates by16.1%,P rates by 43.5%,and the nitrate residues in the 0¹00 cm soil layer by 31.6%,as well as increasing the wheat grain yield by 698 kg hm^–2 and the economic returns by 1984 Yuan hm^–2 compared with CFA.Furthermore,the OFA_OM method increased the N,P and K uptake in wheat respectively by 3.9%,3.2%and 9.3%,compared with CFA,as well as increasing the N and P physiological efficiency by 4.1%and 3.3%,and the partial factor productivity for the applied N,P and K fertilizer by 35.6%,97.0%and 40.8%.Averaged across years and sites the recovery efficiency for N,P and K under OFA_OM were 49.8%,9.8%and 67.3%,respectively,and the corresponding agronomy efficiency were 9.2 kg kg^–1 N,10.2 kg kg^–1 P₂O₅ and 17.1kg kg^–1 K₂O.Under the straw retention conditions,the N,P and K surplus under OFA_OM were28.3 kg N hm^–2,32.5 kg P₂O₅ hm^–2 and 3.8 kg K₂O hm^–2,respectively.Compared with CFA,the N and P surplus under OFA_OM decreased,but the K surplus kept stablity.?3?Ridge mulching and furrow seeding with seed-side-fertilization?RFF?applied the fertilizer in a stripe 5 cm down away from seed row and 5 cm down under plastic film.In RFF,fertilizer was applied by a seeding-mulching-fertilizer machine under the drought-resistant and water-saving cultivation of ridge mulching and furrow seeding,the method increased not only the grain yield,economic return and water use efficiency,but also the water storage in the deeper soil layer at next sowing.Compared with the local conventional cropping pattern without plastic film mulching and uniform fertilization?CP?,averaged across the three experimental years,grain yield increasd by 8.3%under the conventional RF cutivation?ridge mulching and furrow seeding with uniform fertilization?and by 20.1%under RFF,water use efficiency increased by 8.1%under RF and by 16.1%under RFF.The economic returns increased by 23.4%under RFF,however,that under RF had no significant changes in all the three years.The RFF could adjust soil water storage and consumption better than RF with decreasing water consumption in 100²00 cm soil layer in wet year and increasing water harvest during fallow period in dry year,thereby ensuring or even increasing water storage at next wheat sowing.As a result,RFF had higher yield,economic return,and water use efficiency than RF.In dry growing seasons of 2013–2014 and 2015–2016,compared with RF,the yield under RFF was increased by 8.4%and 15.5%,the economic return increased by23.2%and 30.1%,and water use efficiency increased by 7.0%and 10.0%,respectively.In the wet growing season of 2014–2015,the water use efficiency under RFF was 8.0%higher than that under RF,although there was no significant increase of yield under RFF.?4?RFF not only incresased the grain yield of wheat in dryland,but also improved the crop nutrient absorption and its utilization of N,P and K,and significantly increased the uptake efficiency for these nutrients.Therefore,averaged across the three experimental years,RFF significantly increased the grain N and P concentration respectively by 8.2%and 4.1%,and overcomed the problem of grain N concentration decrease caused by RF.Compared with CP,grain N concentration under RF decreased significantly.Compared with RF,RFF increased the nitrate accumulation in 0⁴0 cm soil layer at anthesis and nitrate in 0²00 cm soil layer at harvest,N,P and K accumulation in vegetative organs after jointing stage and these nutrients translocation to grain during the grain filling stage,and thereby increasing N,P and K accumulation in grain.As a result,RFF had significantly higher yield,economic return,grain N and P concentration,and N,P and K uptake efficiency than RF averaged across the three experimental years.Particularly in the dry growing seasons of 2013–2014 and2015–2016,compared with RF,the grain N concentration under RFF was increased by 9.9%and 8.7%,N uptake efficiency increased by 7.0%and 10.0%,and P uptake efficicency increased by 9.0%and 23.5%,respectively.In the wet growing season of 2014–2015,RFF increased the grain N concentration,N and P uptake efficiency by 6.0%,23.3%and 23.5%compared with RF,respectively.In conclusion,optimized fertilization can promote crop nutrient absorption and utilization,enhance the grain yield,economic return and nutrient use efficiency,and reduce the soil nitrate residue at harvest of wheat in dryland.Therefore,the optimized fertilization based on soil test at harvest and regulating fertilizer placement in the drought-resistant and water-saving cultivation is of remarkable significance for cutting down fertilizers,enhancing nutrient use efficiency,increasing grain yield,economic return,and ensuring environmental friendly crop production in dryland with over-high soil nitrate residue due to over-application of chemical fertilizers.