Effect on greenhouse gas balance of converting rice paddies to vegetable production

Abstract

Rice paddies are increasingly being converted to vegetable production due to economic benefits related, in part, to changes in demand during recent decades. Here, we implemented a parallel field experiment to simultaneously measure annual emissions of CH4 and N2O, and soil organic carbon (SOC) stock changes, in rice paddies (RP), rice paddy–converted conventional vegetable fields (CV), and rice paddy–converted greenhouse vegetable fields (GV). Changing from rice to vegetable production reduced CH4 emissions by nearly 100%, and also triggered substantial N2O emissions. Furthermore, annual N2O emissions from GV significantly exceeded those from CV due to lower soil pH and higher soil temperature. Marginal SOC losses occurred after one year of cultivation of RP, CV, and GV, contributing an important share (3.4%, 32.2%, and 10.3%, respectively) of the overall global warming potential (GWP) balance. The decline in CH4 emissions outweighed the increased N2O emissions and SOC losses in CV and GV, leading to a 13%–30% reduction in annual GWP as compared to RP. These results suggest that large-scale expansion of vegetable production at the expense of rice paddies is beneficial for mitigating climate change in terms of the overall GWP.