Modeling Nitrous Oxide Emissions And Nitrate Leaching From Greenhouse Vegetable System By Using A Biogeochemical Model

Recently,nitrous oxide?N₂O?emissions and nitrate?NO₃^-?leaching induced by excess application of nitrogen?N?application and frequent irrigation management from greenhouse vegetable?GV?system were not clear.The impacts of nitrogen management on N₂O emissions and NO₃^-leaching from GV system were still unknown.And the researches on mitigation managements of both N₂O emissions and NO₃^-leaching while maintain yields were still lacking.The field measurements were performed at a GV field in sub-urban of Beijing,China and spanned seven vegetable growing seasons?P1 to P7?.then we tested a process-based model biogeochemical model,Denitrification-Decomposition?DNDC?,for its applicability to assess the impacts of nitrogen management on N₂O emissions and NO₃^-leaching from GV system.The main results were:?1?We measured N₂O emissions under four treatments,including no N fertilizer use?CK?,farmers'conventional fertilizer application?FP?,reduced N fertilizer rate?R?,and R combined with the nitrification inhibitor?dicyandiamide?DCD???R+DCD?.The R and R+DCD treatments significantly?P<0.05?reduced the N₂O emissions under FP by 38.1%to 48.8%and 49.5%to 62.0%,across the three rotational periods,although their mitigation efficiencies were highly variable among different vegetable seasons.This study suggests that GV fields associated with intensive N application and frequent flooding irrigation may substantially contribute to the N₂O emissions.?2?In this study,DNDC was first introduced to intensive GV fields in China and was tested by multiple-year data.We conformed soil bulk density,initial soil NH₄⁺-N,initial soil NO₃^--N,soil texture,initial organic C content at surface soil,and field capacity.We calibrated the physiological parameters?maximum biomass production,thermal degree days for maturity and water demand?and the parameters of inhibitor efficiency and effective duration days.We tested a process-based model biogeochemical model,Denitrification-Decomposition?DNDC?,for its applicability to assess the impacts of nitrogen management on N₂O emissions and NO₃^-leaching from GV system.The results suggested that the modeled influences of N management on vegetable yields were comparable with the observations?RMSE:0.2-32.7?.There exist a zero-intercept linear regression?slope=1.03,R²=0.945,P<0.001?relating the simulations to the observations of the seasonal cumulative N₂O emissions,suggesting that the DNDC model captured the cumulative N₂O emissions across different vegetable growing seasons and treatments?RMSE:6.2–71.5?.The DNDC can capture the magnitudes and patterns of soil temperatures?5cm depth?,topsoil moisture,topsoil NO₃^--N contents?0-20 cm depth?,and NO₃^--N in soil solution?40-50 cm depth?.These suggested that DNDC can be used to simulated nitrogen cycles in GV systems.?3?We also calculated the nitrogen balance based on the simulated data.The rates of N inputs were much higher than the rates of N outputs,and fertilizer application was the main form of N inputs.For example,the vegetable uptake of FP was 305 kg N ha^-1?17.37%?,NO₃^--N leaching was 1180 kg N ha^-1?5.09%?,N₂O and NO esmissions were 22and 3 kg N ha^-1?1.25%and 0.20%?.?4?We assessed the impacts of N and water managements on biomass,N₂O emission and NO₃^-leaching for GV system from North China by utilizing the validated model.Compared with FP treatment,for most scenarios reduce N fertilization rates did not significantly change vegetable yields,but mitigated N₂O emissions?4.50-97.96%?and NO₃^-leaching?4.50-97.96%?.DCD application could mitigated N₂O emissions?0–37.35%?and NO₃^-leaching?0.03–52.98%?without any changes in vegetable yields.Compared with flood irrigation,drip irrigation could increase vegatebe yields,but had different impacts on N₂O emissions and NO₃^-leaching.?5?There exists an exponential correlation between N₂O emission peaks and N leaching peaks for FP treatment?n=14;R²=0.500?.Take both yields and vegetable benefits into consideration,the best management practice?BMP?of reduction in fertilization rates in combination with DCD application and irrigation methods were got,they can maintain vegetable yields while mitigate N₂O emissions?>90%?and NO₃^-leaching?>80%?.