Large CH4 and N2O fluxes can occur from flooded rice (Oryza sativa L.) systems following end-of-season drainage, which contribute significantly to the total growing-season greenhouse gas (GHG) emissions. Field and laboratory studies were conducted to determine under what soil water conditions these emissions occur. In three field studies, GHG fluxes and dissolved CH4 in the soil pore water were measured before and after drainage. Across all fields, approximately 10% of the total seasonal CH4 emissions and 27% of the total seasonal N2O emissions occurred following the final drain, confirming the importance of quantifying postdrainage CH4 and N2O emissions. Preplant fertilizer N had no effect on CH4 emissions or dissolved CH4; however, increased postdrainage N2O fluxes were observed at higher N rates. To determine when postdrainage sampling needs to take place, our laboratory incubation study measured CH4 and N2O fluxes from intact soil cores from these fields as the soil dried. Across fields, maximum CH4 emissions occurred at approximately 88% waterfilled pore space (WFPS), but emissions were observed between 47 and 156% WFPS. In contrast, maximum N2O emissions occurred between 45 and 71% WFPS and were observed between 16 and 109% WFPS. For all fields, gas samplings between 76 and 100% WFPS for CH4 emissions and between 43 and 78% WFPS for N2O emissions was necessary to capture 95% of these postdrainage emissions. We recommend that frequent gas sampling following drainage be included in the GHG protocol of total GHG emissions.
ASJC Scopus subject areas
- Environmental Engineering
- Water Science and Technology
- Waste Management and Disposal
- Management, Monitoring, Policy and Law