| Vegetable planting acreage in China has increased fastly in recent years.With the characteristics of the high level of water and fertilizer inputs,vegetable field always suffers from soil degeneration,high greenhouse gas(GHG)emissions and low nitrogen use efficiency(NUE).Nitrogen(N)application can increase the soil mineral N content while affect the crop yield and soil properties.Meanwhile,long-term N application may result in high GHG emissions and nitrite leaching in agricultural soil.Biochar has been widely applied to many experiments focusing on GHG emission reduction and crop yield enhancement recently in agricultural ecosystems,because biochar amendment can affect the soil N transformation processes.Thus it is necessary to investigate the effects of biochar on GHG reduction,carbon sequestration and soil remediation to achieve the sustainable production in intensified vegetable fieldThere are three sections in this study:(1)A 2.5 year field experiment with 9 consecutive vegetable crops was conducted in a continuously cultivated vegetable cropping system in Nanjing including 9 experimental treatments with three nitrogen levels(0,1240.7 and 1654.3 kg N ha-1 yr-1)and three biochar amendment rates(0,20 and 40 t ha-1),to investigate the effects of biochar amendment(Bc)and nitrogen(N)application on vegetable soil propertities and mineral N content in soil profile;(2)We monitored the annual N2O emissions and vegetable yield by using static chamber-gas chromatographic techniques,to investigate the dynamic responses of N2O emissions and NUE to N application and biochar amendment;(3)To evaluate the effects biochar on degraded vegetable soil,a 44-day RSD(reductive soil disinfestation)field experiment was conducted to monitor the soil properties,dynamic of the mineral N concentrations and the global warming potential(GWP)during the observation period.The main findings are as follows:1.N application significantly increased the soil total nitrogen(TN),soil electronic conductivity(EC),bulk density and soil organic carbon(SOC)by 1.9-25.0%,17.2-241.1%,0.8-9.3%and 7.1-23.4%,respectively,while significantly decreased the soil pH by 0.1-1.19 units during the observation period;Biochar amendment significantly increased the soil TN and SOC by 0.6-16.6%and 4.2-48.3%,respectively,while significantly decreased soil EC and bulk density.Biochar significantly increased soil pH in the plots without N application by 0.11-0.23 units while decreased soil pH by 0.02-0.23 units in N-fertilized treatments.In addition,N application significantly increased the NO3--N concentrations in vegetable soil profile,and biochar significantly increased the NO3--N concentrations in top soil(0-20 cm)while decreased the mineral N concentrations in deeper soil layers.2.During the 9 consecutive vegetable crops planting period,N application significantly increased N2O emissions and N2O-N emission factors by 50.8-158.8%and 8.6-124.6%,respectively.To the contrary,biochar amendment resulted in significant decreases of cumulative N2O emissions,N2O-N emission factor by 4.2-38.9%and 15.9-66.6%,respectively.Dynamic responses of N2O emissions to N and biochar amendment from each vegetable crop seasons were observed during the experimental period.N application significantly increased the N2O emissions of each vegetable crop season,and whereas although without obvious influence during the 1st to 4th vegetable crops,biochar amendment mitigated V2U emissions during the 5th to g9th vegetable crops.3.During the 9 consecutive vegetable crops planting period,N application significantly increased the vegetable yield and yield-scaled N2O emissions by 4.3-39.3%and 13.8-130.6%.The values of NUE were low in this study,varying from 0.4-12.6%.High N input significantly decreased vegetable yield during the 7th to 9th vegetable crops,and thus significantly decreased the N partial factor productivity(PFPN),and no significant differences on NUE were observed between different N level In addition,biochar significantly increased the vegetable yield by 7 7-43.8%,and thus significantly decreased the yield-scaled N2O emissions by 13.8-53.1%while the PFPN and NUE significantly increased with the increasing rate of the biochar amendment.Dynamic responses of PFPN and NUE to N and biochar amendment from each vegetable crop seasons were observed during the experimental period.Compare with N1 level,N application at N2 level significantly decreased the PFPN in the 5th,6th,and 8th crops while had no significant influences on PFPN in the other vegetable crops,and biochar significantly increased the PFPN from each vegetable crops.Moreover,compare with N1 level,N application at N2 level significantly decreased the NUE in 2nd,6th,7th,and 9th vegetable crops while had no significant influences on NUE in the other vegetable crops,and biochar significantly increased the NUE in 2nd to 5th,8th and 9th vegetable crops while had no significant effects on NUE in the other vegetable crops.4.Results showed that the RSD application can significantly decrease the N03~concentrations and electrical conductivity(EC)by 51.4-67.3%and 9.3-14.1%while significantly increasing soil pH and cation exchange capacity(CEC)by 7.9-11.7%and 7.9-13.9%in relation to the control(CK),respectively.Compared with the CF treatment,the RSD application reduced soil NO3-concentrations and EC,while it increased soil pH and CEC in the biochar-amended plots.In addition,the RSD application resulted in a significant increase of GWP by 64.1-130.1%in relation to the CK during the RSD cycles.In addition,compared with the CF treatment,biochar resulted in a decrease in GHG balance by 20.7-28.7%in the RSD field experiment.Therefore,this study indicated that high N fertilizer application can result in soil degeneration,high N2O emissions and low NUE during the intensive vegetable production.Biochar can impove the soil quality and achieve lower N2O emissions,higher vegetable yield and NUE stimutaneously.Dynamic responses of N2O emissionsand NUE to N application and biochar amendment exist in intensive vegetable production.Biochar amendment can be an effective practice which can efficienctly improve the soil quality in degraded vegetable soils in RSD field experiment. |
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