Effects Of Nitrogen Application Rate On Water And Nitrogen Utilization,yield And Grain Quality Of Winter Wheat In Weibei Dryland

The soil nutrient of winter wheat field is relatively poor in Weibei dryland,and the rainfall is scarce during wheat growing season and the annual difference is great,which leads to the difficulty of synchronization of soil nitrogen supply capacity and wheat growth demand.The imbalance of soil water and nitrogen supply is the main factor of low and unstable yield of dryland wheat.Therefore,it is of great significance to explore the relationship between nitrogen fertilizer effect and winter wheat yield,water and nitrogen utilization and grain quality under different rainfall conditions in Weibei dryland,which is of great significance to guide the rational nitrogen application of winter wheat.A 3-year field experiment（2017–2020）of winter wheat（Jinmai 47 and Chang 6359）was performed to evaluate the effects of nitrogen fertilization at five levels(0,60,120,180 and 240kg·hm^-2,represented as N₀,N₆₀,N₁₂₀,N₁₈₀,N₂₄₀,respectively)under different rainfall patterns on water use,growth and physiology,dry matter（nitrogen）accumulation and transportation,yield and quality of winter wheat in Heyang County,located in Weibei dryland of Shaanxi.The results show that:（1）There was a linear correlation between rainfall in fallow period（from July to September）and SWS_S,with an increment of 0.9 mm SWS_S per 1 mm rainfall.In the humid and normal years with adequate rainfall during fallow stage,the SWSs in present winter wheat growth season was not significantly influenced by the increase of nitrogen fertilization in previous growth season.However,in the dry year with less rainfall in fallow stage,the SWS_S in present winter wheat growth season decreased significantly by 15.4 mm when N fertilization in previous growth season was increased by each 100 kg·hm^-2.Compared with dry and normal year,WUE increased by 55.7%and 26.5%,respectively in humid pattern.Compared with N₀ treatment,with nitrogen fertilizer application,increased ET by 4.6—14.6%,6.0—8.6%and 2.2—9.5%,increased WUE by 20.7—39.8%,4.7—33.3%,13.1—35.4%,respectively.（2）During the whole growth period of winter wheat,each physiological index increased first and then decreased.The change trend of Jinmai 47 and Chang 6359 was consistent.The results showed that the rainfall year had significant effect on the growth and physiological index of winter wheat,and the overall performance was as follows:humid year>normal year>dry year.Leaf area index,total chlorophyll,net photosynthetic rate,transpiration rate and single leaf water use efficiency of winter wheat increased with the increase of nitrogen application under different rainfall years.In humid year,N₂₄₀ had the best performance;N₁₂₀ was the best in dry year;N₁₈₀ and N₂₄₀ performed best in normal year.（3）As the nitrogen fertilizer increasing,the dry matter transport,the transport rate and the contribution rate of transport to grain rate in pre-anthesis showed a trend of“first increase and then decrease”,and overall performance was as follows:humid year>normal year>dry year,the variation among varieties was similar.The dry matter translocation before anthesis ranged from 733 to 1488 kg·hm^-2,the translocation rate ranged from 9.5 to20.1%,and the contribution rate ranged from 21.2 to 34.6%.The response characteristics of pre-anthesis nitrogen translocation,translocation rate and contribution rate of pre-anthesis nitrogen translocation to grain nitrogen were consistent with the change trend of dry matter.The amount of nitrogen translocation before anthesis ranged from 40.5 to 73.1 kg·hm^-2,the translocation rate ranged from 43.3 to 57.1 kg·hm^-2,and the contribution rate ranged from53.1 to 67.7 kg·hm^-2.The characteristics of nitrogen utilization showed:wet year>normal year>dry year under different years.Compared with N₀ treatment,nitrogen recovery efficiency（NRE）,nitrogen agronomic efficiency（NAE）and nitrogen partial productivity（NPEP）decreased with the increase of nitrogen application rate,while nitrogen utilization efficiency（NUt E）and nitrogen requirement of 100 kg grain（NRG）showed a trend of“first increase and then decrease”.（4）The grain yield and protein yield were increased by 112.3%and 39.1%,94.4%and31.6%,protein content decreased by 8.3%and 5.2%,respectively in humid year compared with those in dry year and normal year.Compared with N₀,nitrogen application in humid,dry and normal year increased by 7.1—28.1%,1.5—34.1%and 8.5—28.9%respectively,and protein yield increased by 13.7—42.4%,12.1—55.8%and 26.0—54.2%respectively,protein content by 5.6—10.4%,10.1—17.7%and 8.5—15.6%,respectively.The net output value and the ratio of output to input increased first and then decreased with the increase of nitrogen application rate.Compared with N₀ treatment,the net output value and the ratio of output to input increased by 1.5—3.9 times and 10.1—31.2%respectively.Under the same fertility condition,the net output value of Jinmai 47 was 1073 yuan·hm^-2 higher than that of Chang 6359,and the ratio of output to input increased by 15.1%.Grain protein content,wet gluten content,bulk density,sedimentation value and other quality parameters increased with the increase of nitrogen application under different rainfall years,but the best N treatment was not consistent.Among them,N₁₈₀ was the best among the N treatments in wet and normal years,whereas N₁₂₀ was the best in dry year.（6）In this study,we established and verified the critical nitrogen dilution curves of winter wheat based on aboveground dry matter under three rainfall years in Weibei dryland(a.humid type:Nc=3.90DM^-0.459;b.dry type:Nc=3.06DM^-0.282;c.normal type:Nc=3.58DM^-0.484).The variability of model parameters was as follows,a:humid>normal>dry,b:humid=normal>dry.The results showed that the nitrogen nutrition index（NNI）of N₀ and N₆₀ were less than“1”under three rainfall conditions,indicating the existence of nitrogen deficit.The NNI of N₂₄₀ was significantly higher than“1”,which showed that there was nitrogen surplus and luxury absorption.NNI values at different growth stages were significantly positively correlated with grain yield,and negatively correlated with NAE,NRE and NPFP.Therefore,NNI can further explain the nitrogen profit and loss of dryland winter wheat at the key growth stages under different rainfall years.Comprehensive evaluation based on the above research,the optimal nitrogen application schemes for humid year,dry year and normal year are 180—200,110—120 and150—170 kg·hm^-2,respectively.And the model of“applying nitrogen according to rain”can be adopted,which can not only meet the requirements of stable yield and high quality of winter wheat in dryland,but also ensure water efficient use.