Effects Of Nitrogen Reduction And Biochar Application On Wheat Productivity And Soil Quality In Dryland

Water resource shortage and nutrient deficiency are the main limiting factors for crop growth in dryland area of the Loess Plateau.Rational application of nitrogen fertilizer is an important measure to improve the yield and water use efficiency of dryland winter wheat.Biochar application can change soil physical and chemical properties and improve crop yield and water and fertilizer utilization efficiency,which is one of the main focuses of agricultural production at present.Due to different types of biochar,soil types and study area conditions,there are still many controversies about the regulation effects of biochar and its combined application with nitrogen fertilizer on soil quality in dryland farmland.Therefore,based on the field location experiment,this study investigates the regulation effects of different nitrogen application amounts,different biochar application amounts,and nitrogen reduction combined with biochar application on the growth,dry matter accumulation,nutrient absorption and distribution of wheat,soil nitrate nitrogen accumulation,water use efficiency,soil microbial community and soil fertility quality in dryland.The main results obtained are as follows:1.Nitrogen application significantly increased the yield of winter wheat.With the increase of nitrogen application rate,the amount of nitrogen accumulation and transfer before anthesis and the absorption of nitrogen,phosphorus and potassium by grains increased.The effect of biochar on wheat yield was related to rainfall year type.The addition of biochar increased nitrogen accumulation after anthesis,and 30 t ha^-1 biochar application significantly increased dry matter accumulation in aboveground,nitrogen and phosphorus accumulation in grain and aboveground,and potassium accumulation in stem and aboveground at mature stage.Compared with conventional N application,reduced N application did not significantly affect wheat yield under 20 t ha^-1 biochar treatment,but significantly reduced the total nitrogen and potassium accumulation in shoot and nitrogen accumulation before anther.2.Fertilization increased the nitrate accumulation in 0-100 cm soil layer.Compared with conventional nitrogen application,soil apparent N loss decreased by 21.3 kg ha^-1 and N use efficiency increased by 10.9 kg kg^-1.Compared with the untreated treatment,biochar application reduced the apparent N loss by 9.3-24.6 kg ha^-1 and increased the residual nitrate N in 0-100 cm and 100-200 cm soil layers by 30 t ha^-1biochar application.Nitrogen reduction combined with biochar reduced apparent N loss and increased N partial productivity.3.Nitrogen application,biochar and rainfall year patterns significantly affected soil water consumption and wheat water use efficiency in dryland feild.In 2019-2020（with little rainfall in March and April）,soil water consumption was mainly concentrated in the 100-200cm layer from flowering stage to maturity stage,while in 2020-2021（with sufficient rainfall in March and April）,soil water consumption was mainly concentrated in the 0-100 cm layer.The application of nitrogen fertilizer reduced the soil water content of 0-200 cm layer at flowering stage and maturity stage,and increased the consumption of available water storage from jointing stage to flowering stage.The maximum water use efficiency（WUE）under conventional fertilization treatment was 1.34 kg m^-3.The application of 10 and 30 t ha^-1biochar increased the consumption of soil available water storage from pre-sowing stage to jointing stage,and decreased the consumption of soil available water storage from jointing stage to flowering stage.Compared with conventional N application,reduced N application significantly increased soil water storage in 0-20 cm soil layer under 20 t ha^-1 biochar treatment and soil available water storage consumption from pre-sowing stage to jointing stage.4.Different N application rates,biochar application rates and nitrogen reduction combined with biochar application rates did not change the main phyla of soil microorganisms in wheat fields,but changed the relative abundance of different phyla.The dominant phyla of soil microorganisms were Ascomycota,Arthropoda,Streptophyta,Mucoromycota and Basidiomycota.N application did not significantly affect soil microbialαdiversity.Compared with low biochar（B1）treatment,high biochar（B5）application significantly increased Coverage index and decreased Chao1 index and ACE index.Nitrogen application reduction combined with biochar application did not significantly affect soil microbialαdiversity in wheat field.5.Nitrogen application significantly increased the content of soil dissolved organic carbon（DOC）and decreased the content of soil available phosphorus（AP）,but did not significantly affect the quality of soil fertility in dryland wheat field.High biochar application(30 t ha^-1 and 50 t ha^-1)significantly increased the contents of soil organic carbon（SOM）,soil total nitrogen（TN）,soil total phosphorus,（TP）,DOC,soil ammonium nitrogen（NH4+-N）,soil available phosphorus（AP）,soil microbial biomass nitrogen（MBN）,and improved soil fertility quality.Compared with conventional N application,reduced n application had no significant effect on soil fertility under 20 t ha^-1 biochar treatment.In conclusion,nitrogen application increased wheat yield and nitrogen accumulation before anthesis.Proper amount of biochar application could increase postanthesis N accumulation,decrease apparent N loss and increase soil fertility.Nitrogen reduction combined with biochar application had no significant effect on wheat yield and soil fertility.Therefore,biochar application is one of the key technologies to regulate soil fertility quality,reduce chemical nitrogen fertilizer application and improve nitrogen use efficiency in dryland.This study can provide important technical reference for applying biochar to fertilize soil,improving cultivated land quality,reducing nitrogen application rationally and ensuring stable wheat yield in dryland of the Loess Plateau.