Effect Of Biochar Slow-release Nitrogen Fertilizer On Nitrogen Utilization Efficiency Of Brassica Napus L.and Mechanism

Biochar-based nitrogen fertilizers have received increasing attention from researchers;however,the majority of research has focused on their mechanisms of action.Therefore,the effects of this type of fertilizer on soil fertility,plant growth,nitrogen use efficiency（NUE）,and the underlying mechanisms under agricultural conditions remain to be elucidated.Pot experiments were carried out to study the effects of Urea and biochar-based controlled-release nitrogen fertilizer（BCRNF）application on soil fertility and nitrogen fertilizer use efficiency of rape in Southern China and it could provide reference for the application and dissemination of BCRNF in agriculture production.An experiment was conducted to investigate the effects of Urea and BCRNF on rape biomass and yield,soil inorganic nitrogen in different growth stages,N uptake of rapeseed,physiological characteristics of rape,soil microbial and enzyme activity.The result showed that:1.Enhanced N availability to improve NUE and grain yield by BCRNF.The concentration of NO₃^--N were significantly increased by 66.1%and 63.0%with BCRNF application at flowering stage and harvest stage and the concentration of NH₄⁺-N was obviously increased by 28.9%and harvest compared with the Urea treatment,thus ensured the constant N apply to the rape.When compared with Urea treatment,total nitrogen uptake and biomass in rape was significantly increased by BCRNF during the bolting stage and flowering stage.In eventually,the increased yield by 16.9%,NUE was increased by 66.4%and the NAE raised up to 52.9%.2.Improving microbial activity and shifting bacterial communities with high nutrient metabolic cycle ability by BCRNF.Soil microbial carbon and phosphorus was higher than urea treatment at an extremely significant level by 44.9%、181.5%with BCRNF application in the late growth stage of rape.In addition,the activity of soil urease,FDA hydrolase was significantly increased by 8.9%、35.9%.At the same time,enhanced the abundance of（Cyanobacteria,Saccharibacteria,Hyphomicrobiaceae and Sphingomonadaceae）,which contributes to soil nutrient metabolism.3.Increasing N nitrification by stimulating amoA gene expression in ammonia-oxidizing bacteria under BCRNF.BCRNF treatment significantly increased the soil nitrification potential during rapeseed and harvest,which was 41.6%and 15.0%higher than that of urea treatment.Real-time quantitative PCR analysis showed that BCRNF promoted the expression of amoA gene in AOB,increased soil nitrification potential and enhanced nitrification.It accelerates the conversion of NH₄⁺to NO₃^-;inhibits the abundance of denitrifying bacteria nirS and nirK,and reduces the loss of NO₃^-in soil,which improved soil NO₃^--N content during the growth stage of rapeseed.These results demonstrate that BCRNF mainly increased soil inorganic nitrogen at later stages,enhanced soil microbial biomass nitrogen and enzyme activity,promoted the slow release of nitrogen to increase nitrogen availability,and modulating functional microbial feedback through increased soil nitrification and reduced denitrification.thereby increased N uptake of rape,then increased NUE,NAE,promoted rape growth,and increased grain yield.