Effects Of Nitrogen Fertilizer And Biochar Application On Yield-scaled NO And N₂O Emissions From An Intensive Vegetable Ecosystem

Agro-ecosystem plays an important role in the land ecosystem,which is considered as a major source of NO and N2O emission.Intensive vegetable field as a special agro-ecosystem,with the characteristics of the high level of fertilizer inputs.Excessive application of nitrogen fertilizer will cause a large amount of NO and N2O emissions,causing a series of environmental problems such as the global greenhouse effect.However,a lot of studies have been done on NO and N2O emissions from staple crops,few researches have focused on simultaneously measuring NO and N2O from field vegetable systems.Meanwhile,due to its large surface area and high stability,biochar can slow soil acidification,reduce soil mineral nitrogen leaching,maintaining soil fertility for a long time and promote crop growth.There is growing interesting in using biochar as an effective method to reduce NO and N2O emissions from agricultural soils in recent years.However,the long-term effects of biochar on NO and N2O emissions and crop yield still pay more attention.Thus it is necessary to continuously monitor the long-term efficacy of biochar in agro-ecosystems,which can provide theoretical bais for the rational applications of biochar in agriculture ecosystem.This study was started in 2016,with two factors including biochar application and nitrogen fertilization,there were six treatments in total and each treatment was replicated three times.Crop yield,NO and N2O were monitored from 2016 to 2018,Soil properties were analyzed to evaluation of long-term effects of biochar on GHGs and yield increase.The main findings are as follows:1.N application significantly increased the total nitrogen(TN)by 6.2-12.0%,while significantly increased the electrical conductivity(EC)and soil bulk density 4-66.7%and 5.5-10.52%,respectively,and significantly decreased soil pH.The soil organic carbon(SOC)is affected by the interaction between N and biochar.Biochar amendment significantly increased soil TN,SOC,pH,by 2.1-9.0%,7.1-34.0%and 1.1-2.9%,respectively,while significantly decreased the soil bulk density.The soil EC is affected by the interaction between biochar and N.Compared with aged biochar treatment,fresh biochar resulted in an increase in soil pH,while decreased soil organic carbon(SOC).In addition,N application significantly increased the inorganic nitrogen concentrations(NH4+-N,NO3--N,NO2--N),while biochar amendment significantly decreased the NO2--N concentrations.2.Biochar amendment significantly increased the yield of vegetables.Compared with fresh biochar treatment,aged biochar obviously increased crop yield.3.Soil temperature and the inorganic nitrogen concentrations had significant positive correlation with NO emission(P<0.01).In addition the soil WFPS had a significant positive correlation with NO emission(P<0.05).During the observation period,N application significantly increased the cumulative NO emission,NO emission factors and the yield-scaled NO.On the contrary,biochar amendment significantly decreased the cumulative NO emission,NO emission factors and and the yield-scaled NO.In addition,since field-aged biochar showed obvious effects on GHGs mitigation after 4 years,biochar incorporations had long-term effect on NO mitigation in the intensive vegetable system.No significant difference between the fresh biochar and aged biochar in the NO mitigation.4.Soil temperature,WFPS and the inorganic nitrogen concentrations(NH4+-N and NO2--N)had significant positive correlation with N2O emission(P<0.01).In addition the NO3--N concentrations had a significant positive correlation with N2O emission(P<0.05).During the observation period,N application significantly increased the cumulative N2O emission,N2O emission factors and the yield-scaled N2O.On the contrary,biochar amendment significantly decreased the cumulative N2O emission,N2O emission factors and the yield-scaled N2O.In addition,since field-aged biochar showed obvious effects on GHGs mitigation after 4 years,biochar incorporations had long-term effect on GHGs mitigation in the intensive vegetable system.However,no significant difference between the fresh biochar and aged biochar existed in the GHGs mitigation.Therefore,this study indicated that high N fertilizer application resulted in soil degeneration,high NO and N2O emissions during the intensive vegetable production.Biochar could improve the soil quality.In addition,biochar incorporations had long-term effect on NO and N2O mitigation and crop improvement in the intensive vegetable system.