Greenhouse gas footprints of maize cultivation systems in different climate zones: Field data validation and application of CNMM--DNDC as a hydro-biogeochemical model

Accurate quantification of life-cycle greenhouse gas (GHG) footprints (GHGfp) for a crop cultivation system is urgently needed to address the conflict between food security and global warming mitigation. In this study, the hydro-biogeochemical model, CNMM-DNDC, was validated with in-situ observations from maize-based cultivation systems at the Yongji (YJ, China), Yanting (YT, China) and Madeya (MA, Kenya) sites, subjected to temperate, subtropical and tropical climates, respectively, and updated to enable life-cycle GHGfp estimation. The model validation provided satisfactory simulations on multiple soil variables, crop growth and emissions of GHGs and reactive nitrogen gases. The locally conventional management practices resulted in GHGfp values of 0.35 (0.09~0.53 at the 95% confidence interval), 0.21 (0.01~0.73), 0.46 (0.27~0.60) and 0.54 (0.21~0.77) kg CO2e kg−1 d.m. for maize−wheat rotation at the YJ and YT sites, and for maize−maize and maize−Tephrosia rotations at the MA site, respectively. The YT site’s smallest GHGfp was attributed to its lower off-farm GHG emissions than the YJ site, though the slightly lower soil organic carbon (SOC) storage and maize yield than the YJ site. The MA site’s highest SOC loss and low yield in shifting cultivation for maize−Tephrosia rotation contributed to its highest GHGfp. Optimized management practices of maize cultivation at these sites could be optimized by combination of synthetic and organic fertilizer(s) while incorporating 50~100% crop residues. Further evaluation of the updated CNMM-DNDC is needed for different crops at site and regional scales to confirm its worldwide applicability in quantifying GHGfp and optimizing management practices for achieving multiple sustainability goals.