Assessing impacts of nitrogen management on nitrous oxide emissions and nitrate leaching from greenhouse vegetable systems using a biogeochemical model

Greenhouse vegetable (GV) fields with intensive nitrogen application and frequent flood irrigation may substantially contribute to reactive nitrogen (Nr) losses, such as nitrous oxide (N2O) emissions and nitrate (NO3-) leaching. In this study, we applied a biogeochemical model, Denitrification-Decomposition (DNDC), to assess impacts of N management on vegetable yields, N2O emissions, and NO3--N leaching from GV systems. The model was evaluated using multi-year (2011-2013) field measurements of vegetable yields, N2O emissions, and NO3--N concentrations in the surface soil layer and soil leachate under three treatments with different N management. The model evaluations demonstrated that the simulations of the vegetable yields and seasonal cumulative N2O emissions were consistent with the corresponding observations after calibration. In addition, DNDC generally captured the seasonal variations of the N2O fluxes and NO3--N concentrations in the surface soil layer and the seasonal patterns and magnitudes of the measured NO3--N concentrations in soil leachate in 2011. We then assessed impacts on the vegetable yields, N2O emissions, and NO3--N leaching of different N management practices by conducting simulations under scenarios with changes in rate of the applied N-fertilizers and the application of nitrification inhibitor (NI). The results suggested that 1) the increasing of organic or synthetic N application rate generally increased the N2O emissions and NO3--N leaching, but did not persistently increase the vegetable yields, 2) urea N application could induce more N2O emissions and NO3--N leaching in comparison with organic N amendment, and 3) the NI application could decrease the N2O emissions and NO3--N leaching while maintaining the vegetable yields at the GV fields. The optimum management practice identified in this study was applying organic manure at a rate of 320 kg N ha(-1) four season(-1) and urea at a rate of 334 kg N ha(-1) four season(-1), combined with the NI application. The optimum management practice reduced the rates of organic manure (1600 kg N ha(-1) four season(-1)) and urea (1670 kg N ha(-1) four season(-1)) under the farm's conventional practice by 80%. This practice maintained or slightly increased the yields and mitigated the N2O emissions and NO3--N leaching by 81% to 90% and 92% to 95%, respectively, among different vegetable growing seasons.