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The cropping system conversion, from rice to vegetable, showed various influences on the greenhouse gases (GHG) emission with conversion time and fertilizer/irrigation management. In this study, we evaluated the DeNitrification-DeComposition (DNDC) model for predicting carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) emissions and crop yields as rice converted to vegetable cropping system under conventional or no fertilization from 2012 to 2014. Then, we quantified the long-term (40 years) impacts of rice-vegetable cropping system conversions and fertilization levels (0, 50, 100 and 150% conventional fertilization rate) on GHGs emissions and global warming potentials (GWP) using the calibrated model. The DNDC model-simulated daily GHG emission dynamics were generally consistent with the measured data and showed good predictions of the seasonal CH4 emissions (coefficient of determination (R2) = 0.96), CO2 emissions (R2 = 0.75), N2O emissions (R2 = 0.75) and crop yields (R2 = 0.89) in response to the different cropping systems and fertilization levels across the two years. The overall model performance was better for rice than for vegetable cropping systems. Both simulated and measured two-year data showed higher CH4 and CO2 emissions and lower N2O emissions for rice than for vegetable cropping systems and showed positive responses of the CO2 and N2O emissions to fertilizations. The lowest GWP for vegetable without fertilization and highest the GWP for rice with fertilization were obtained. These results were consistent with the long-term simulation results. In contrast to the two-year experimental data, the simulated long-term CH4 emissions increased with fertilization for the rice-dominant cropping systems. The reasonable cropping systems and fertilization levels were recommended for the region. [ABSTRACT FROM AUTHOR]

Crop yield and water use efficiency (WUE) in a wheat-maize double cropping system are influenced by short and uneven rainfalls in the North China Plain (NCP). A 2-year experiment was conducted to investigate the effects of irrigation on soil water balance, crop yield and WUE to improve irrigation use efficiency in the cropping system. Soil water depletion (ΔSWS) by crop generally decreased with the increase of irrigation and rainfall, while ΔSWS for the whole rotation was relatively stable among these irrigation treatments. High irrigations in wheat season increased initial soil moisture and ΔSWS for subsequent maize especially in the drought season. Initial soil water influenced mainly by the irrigation and rainfall in the previous crop season, is essential to high yield in such cropping systems. Grain yield decreased prior to evapotranspiration (ET) when ET reached about 300 mm for wheat, while maize showed various WUEs with similar seasonal ET. For whole rotation, WUE declined when ET exceeded about 650 mm. These results indicate great potential for improving irrigation use efficiency in such wheat- maize cropping system in the NCP. Based on the present results, reasonable irrigation schedules according to different annual rainfall conditions are presented for such a cropping system. [ABSTRACT FROM AUTHOR]