Tailoring Fertilizer Application To Precipitation And Yield For Dryland Wheat In The Loess Palteau

Water and nutrients are the two main factors limiting wheat production in the Loess Plateau,and they have great interactions.Nutrient input may obtain a good harvest in a wet year while a poor harvest in another.“Matching fertilizer to yield predicted by water”is an effective way for improving both dryland wheat yield and nutrient use efficiency.As most methods on fertilizer to precipitation are empirical,it is so far a gap in the knowledge of quantitative relation between precipitation,yield and nutrient uptake.From 2009 to 2016,field experiment combined with on-farm survey of site and year combinations were conducted for dryland winter wheat in the Loess Plateau.Based on the innovated method“yield based evaluation on fertilizer application”,the situation of farmers'fertilizer application were clarified and its influence on soil nutrient supplying were evaluated.Then,the relationships between precipitation,yield and nutrient uptake were quantified for the method“quantitative fertilization based on precipitation for dryland wheat”,with which the potential of fertilizer reduction and yield improving associates with their economic and environmental effect were evaluated.?1?Insight into the yield variation,farmers'fertilizer application were clarified.Main problems of fertilizer application in dryland wheat production were:for N,farmers in very low and low yield groups should reduce their current high N input;for P,farmers in each group should reduce their high P input;and for K,farmers with no K input should use K fertilizer.A 7-yr on-farm survey of 1 561 farmers in 8 counties indicated the farmers'wheat yields ranged from 750 to 9000 kg/ha,with the average of 4217 kg/ha,and they were allocated into five groups as:very low?<2640 kg/ha?,low?2640-3780?,moderate?3780-4920?,high?4920-6060?and very high?>6060?,respectively,accounting for 20.7%,24.1%,20.5%,21.9%and 12.8%of the total.Farmers'N application rates ranged from 33 to454 kg N/ha with an average of 188 kg N/ha,P ranged from 0 to 435 kg P₂O₅/ha with an average of 125 kg P₂O₅/ha,and K ranged from 0 to 201 kg K₂O/ha with an average of 19 kg K₂O/ha.With the increase of grain yield levels,the proportion of N over application farmers decreased from 97.8%in the very low yield group to 18.0%in very high group,Similar to N,the proportion of P over application farmers decreased from 99.1%in very low yield group to69.0%in very high yield group.Different from N and P,K deficient application was practiced by more than 61.0%of farmers in each yield group.?2?Over application of N by local farmers significantly increased the residual nitrate N in 0-100 cm soil layers;but over application of P had no effect on soil available P;deficient application of K significantly decreased soil available K in the 0-20cm soil layer.On-farm survey of 180 farmers combined with field sampling were conducted from2015 to 2016.Comparing farmers'fertilizer rate with the corresponding wheat shoot nutrient uptake indicated:with over N application,the apparent N surplus was 91 kg N/ha,which significantly increased nitrate N accumulation in 0-100 cm soil by 33%;with over P application,the apparent soil P surplus was 91 kg P₂O₅/ha but had no effect on soil available P;with K deficient application,the apparent soil K surplus was-25 kg K₂O/ha and significantly decreased the soil available K by 30%in 0-20 cm soil layer.?3?We quantified relations between grain yield and precipitation in two periods:summer fallow,and summer fallow to jointing,and between crop nutrient requirement and grain yield.Then,the method“fertilization to the already known precipitation”were outlined and test,and adjusting fertilizer to precipitation could correct the over application for N and P,and deficient application for K fertilizer in the Loess Plateau.Based upon field experiments at 52 sites from 2009 to 2013,results indicated wheat grain yield?kg/ha?increased quadratically with summer fallow precipitation?X₁,mm?;and summer fallow to jointing precipitation?X₂,mm?,?Y₁=-0.0200X₁²+25.89X₁-2367,r²=0.59,Y₂=-0.0148X₂²+23.38X²-3179,r²=0.69?.The shoot N,P and K nutrient uptake were linearly correlated with grain yield.Basal fertilizer requirement was calculated from target grain yield estimated as a function of fallow precipitation.The need for topdressing was determined by re-estimating target grain yield as a function of precipitation during summer fallow until jointing stage.?4?Insight into the respond of wheat yield to precipitation,fertilizer rate in a rational range were suggested for dryland wheat with large yield variation,then potential of fertilizer reduction and yield improving associates with their economic and environmental effect were evaluated.Compared with the recommended N,over-,rational-and deficient N application were practiced by 56%,38%and 7%of 1561 farmers.If farmers with over N use adjusting N input to precipitation,80 kg N/ha and 374 yuan/ha will be saved with N use efficiency increasing from 17 kg/kg to 32 kg/kg,soil nitrate N accumulation decreasing from 202 kg N/ha to 96 kg N/ha,N₂O emission decreasing from 1.2kg N/ha to 0.7kg N/ha and NH₃ volatilization decreasing from 35 kg N/ha to 19 kg N/ha.In general,with the aim of“predicting yield by precipitation,quantified nutrient uptake by yield,adjusting fertilizer to nutrient required,and synergy of high efficiency of water and nutrient use”,Based on“yield based evaluation for fertilizer application”,main problems of fertilizer application were farmers in very low and low yield groups should reduce their current high N input;farmers in each group should reduce their high P input;and farmers with no K input should use K fertilizer.Over application significantly increased the residual nitrate N,deficient application of K significantly decreased soil available K.Relations between summer fallow precipitation,precipitation in summer fallow to jointing,crop nutrient requirement and grain yield were quantified.Then,the method“fertilization to the already known precipitation”were outlined and test,and adjusting fertilizer to precipitation could correct the over application for N and P,and the deficient application for K fertilizer.Fertilizer rate in a rational range were suggested for dryland wheat with large yield variation,then the potential of fertilizer reduction and yield improving associates with their economic and environmental effect were evaluated.The method and results could be helpful for researching and optimizing the theory of water and nutrient management.