Reactive Gaseous Nitrogen Emissions Intensity In Intensive Vegetable Soils And Mitigation Strategy

Vegetable cropping aera has increased significantly in recent years.Intensive vegetable cultivation is characterized by high nitrogen(N)application rates,high cropping index and frequent farming practices,which results in soil degeneration,high reactive gaseous nitrogen emissions(GNrEs)and low nitrogen use efficiency.Biohcar has been suggested to increase soil carbon storage and crop yield by improving soil quality and affecting soil N transformation processes;Nitrification inhibitor can delay nitrification process and reduce N loss,which leads to increasing crop yield and decreasing environment pollution.Therefore,it is necessary to investigate the effects of biochar and inhibitor incorporation on soil quality,vegetable yield and GNrEs and its intensity(GNrI)in intensive vegetable soils in China,which can provide theoretical bais for the rational applications of biochar and nitrification inhibitor in agriculture ecosystem.Therefore,we used the pot experiments and field experiments simultaneously in the present study,which were divided into the following four sections:(1)To identify the GNrI and its soil driving factors in the four vegetable soils sampled from Hunan,Shanxi,Shandong and Heilongjiang Provinces in background.The GNrEs,namely,nitrous oxide(N2O),nitric oxide(NO)and ammonia(NH3)were simutaneously measured using a static opaque chamber-chromatography and NO-NO2-NOx analyzer and ventilation methods,respectively,and vegetable yileds were monitored during the consectutive five vegetable planting seasons at the Pailou greenhouse experiment station of Nanjing Agricultural University;(2)To invegstigate the effects of two different types of biochar(Bw and Bm)on soil quality,vegetable yield,GNrEs and GNrI in intensive vegetable soils during the one-year pot experiment;(3)To invegstigate the effects of two different types of nitrification inhibitors(CP and DCD)on soil quality,vegetable yield,GNrEs and GNrI in intensive vegetable soils during the one-year pot experiment;(4)The field trial was conducted by setting six treaments under three biochar amendment rates(0'20,40 t hm-1)with nitrogen fertilizer or nitrogen mixed with nitrification inhibitor to study the the combined effects of nitritrification hibitor and biochar incorporation on soil quality,vegetable yield,NUE and yield-scaled N2O emissions from an intensively managed vegetable field in Nanjing.The main fingdings are as follows:1.The GNrEs differed significantly among the different types of vegetable soil:in terms of N2O and NO emissions,the highest emissions occurred in Hunan soils,followed with Heilongjiang soils,whereas the relatively low emissions were in Shanxi and Shandong soils;Shanxi soil emitted the lowest NH3 emissions,and no significant differences exsited among other soils.Additionally,there were pronounced differeces in vegetable yields among all the vegetable soils:the highest yields for Heilongjiang were 64.64 t ha-1 and the relatively low yields for Shanxi and Shandong were 26.82 and 29.75 t ha-1,respectively,with the yields for Hunan in middle.Collectively,the highest GNrI for Hunan reached up to 0.61 kg N t-1,whereas the lowest for Heilongjia was 0.10 kg N t-1.According to the reduance analysis,we found the followings:soil N2O emissions were mainly affected by the concentrations of NH4+-N,and had negative relations with soil pH;both NH4+-N and sand contents were the two important factors regulating soil NO emissions;soi TN was the main factor driving NH3 emissions;there was a positive relationship between soil SOC contents and vegetable yield.2.Biochar amendments increased the SOC,TN,and EC by 20.4-135.0%,0.5-21.2%and 2.4-38.1%,respectively,and decreased NH4+-N concentrations to some degree,with the effects on MBC,PNR and DEA being affected by soil types.Compared with Bw,Bm amendment significantly increased PNR in Hunnan and Shanxi soils.Additionally,biochar amendments increased vegetable yields in Shandong and Heilongjiang soils by 1.7-30.5%,but had no effects in Hunan and Shanxi soils.Compared with Bw,Bm amendment enhanced vegetable yields by 11.6-20.2%across all the soils.Biochar amendments had significant influences in soil N2O and NO emissions but not for NH3 emissons.Detailly,biochar amendments significantly reduced the N2O emissions in Shanxi and Heilongjiang soils by an average of 56.5%and 47.4%,respectively,and the NO emissions in Hunan by 49.5-57.0%,but produced no influences in Shandong soil.Compared with Bm,Bw amendment decreased the emissions of soil N2O and NO more efficiently,whereas Bm was more prone to stimulate NH3 emissions than Bw.Biochar amendments had significant influences in GNrI,decreasing it in Shanxi and Heilongjiang soils by an average of 18.0%and 25.0%,respevtively,and no pronounced differences were observed betweens the two types of biochars.3.Nitrification inhibitor applications increased soil NH4+-N by 0.3-41.1%but decreased NO3--N by 6.3-34.4%,and enhaced soil pH and EC to different degrees,with effects on MBC being affects by soil types.Nitrification inhibitor applications significant reduced PNR in Shanxi and Heilongjiang soil by 26.3-50.0%and 22.5-56.8%,respectively.Compared with CP,DCD was more effective in decreasing PNR in Shanxi and Heilonjiang soils by 32.1-44.3%.No significant influences on DEA were detected with Nitrification inhibitor additions across all soils.Nitrification inhibitor applications decreased N2O and NO emissions by 1.8-61.0%and 0.8-79.5%,respectively,but promoted NH3 volatilization by 3.2-44.6%across all soils.Significant positive correlations were observed between inhibited N2O+NO emissions and stimulated NH3 emissions with nitrification inhibitor additions across all soils.Nitrification inhibitor applications significantly reduced GNrI in Shanxi and Shandong soils by an average of 18.1%and 10.9%,repecitively and no notable differences were observed between the two types of nitrification inhibitor.4.Nitrification inhibitor treatment had no sifnificant influences in soil TN and SOC,whereas biochar amendment increased soi TN and SOC by 81.5-99.3%and 66.9-85.1%.Additionally,nitrification inhibitor addition enchanced soil pH by 0.97-2.15 units while biochar amendment significantly decreased it by 0.45-1.63.Both nitrification inhibitor and biochar additons increased vegetable yield by 9.7-60.5%and 7.0-43.1%,N partial factor productivity(PFPN)by 6.3-43.8%and18.4-68.2%,and decreased the cumulative N2O emissions by 18.6-39.2%and 3.7-13.4%,yield-scaled N2O emissions by 23.6-57.7%and 20.6-39.4%,respectively,during the field experiment period.Therefore,this study showed that the GNrI differed significantly among intensive vegetable soils in China,which were affected by soil properties.Biochar amendments can improve soil quality and achieve to decrease GNrI by mitigating GNrEs or increasing vegetable yiled,and those effects were largely affected by soil and biochar types.Nitrification inhibitor application can also change soil properties,and mitigated GNrI by reducing N2O and NO emissions and enchacing vegetable yield.The incorporations of nitrification inhibitor and biochar effectively increased vegetable yield and PFPN,but decreased N2O emissions,thus resulting in significantly decreasing the yield-scaled N2O emissions.