Maize and rice double cropping benefits carbon footprint and soil carbon budget in paddy field

Cropping systems in double rice paddies in subtropical region of China are under conversion to a rice-upland rotation or upland crops production driven by economic benefits and social conditions. However, limited studies have been completed to evaluate the productivity and environmental consequences following the introduction of maize to paddies in this area. Four cropping systems were practiced in our experimental field plots: traditional double rice (R-R), maize-rice rotation (M-R), rice-maize rotation (R-M) and double maize cropping (M-M). The two-year study showed that conversion to maize-related cropping patterns led to a substantial change in GHG emissions, carbon footprint and net soil carbon budget (NSCB) on a short-term timescale. Although the M-M treatment resulted in a 13.5% higher annual grain yield than the R-R treatment, it showed a tremendous increase in total CO2 eq emissions of 47.7% and higher soil carbon loss, thus, it had a higher carbon footprint than the R-R treatment by 30.7% (p < 0.05). The annual sequence of rice and maize rotation showed different features in system functions as well. The R-M rotation could not be an option to replace R-R cropping because of its higher carbon footprint and soil carbon loss. However, compared to the R-R treatment, the M-R rotation increased the annual grain yield by 18.3% (p < 0.05) and, showed comparable total CO2 eq emissions and a lower carbon footprint (1.67 kg CO2 eq.kg(-1)). Nevertheless, the M-R treatment still displayed a high soil carbon loss (-2127 kg C ha(-1) by NSCB analysis) after two crop seasons of cultivation, while the R-R cropping maintained the soil carbon gain. Overall, the M-R rotation could be the better alternative cropping system in paddies in subtropical regions in China. Further studies regarding proper management practices to reduce soil carbon loss under M-R rotation are needed to realize its dual benefits of higher grain yield and lower impact on the soil carbon pool.