Effects of Different Water Management and Fertilizer Applications on CO2 Fluxes from a Selected Myanmar Rice (Oryza sativa L.) Cultivar

The application of nitrogen fertilizer and the water management practices are important to optimize potential yields in rice cultivation. Moreover, they may affect the emissions patterns of methane (CH4) and carbon dioxide (CO2) emission. Compared to methane, knowledge about the combined effects of different fertilizer rates together with different water management practices on CO2 fluxes are scarce. Therefore, this study aims to assess CO2 fluxes of a selected rice cultivar in response to different fertilizer applications and water management practices. The treatments included two different applications of inorganic fertilizer (recommended rate and farmer’s practice), organic manure application and water management practices; continuous flooding (CF) and alternate wetting and drying (AWD). Mean total CO2 flux in CF was -30.82 g CO2 m-2 d-1 during daytime and 29.64 g CO2 m-2 d-1 during nighttime. Surprisingly, the average net CO2 fluxes were negative under both CF (-49 mg CO2 m-2h-1) and AWD practices (-127 mg CO2 m-2h-1), indicating a net CO2 uptake by the rice plants. Inorganic fertilizer applications led to considerably higher net CO2 emissions compared to the control under both CF and AWD. Conversely, CO2 emission fluxes in the treatment with organic manure showed negative net CO2 fluxes under both water management practices and while revealing the same fresh biomass as observed in other treatments (inorganic fertilizer and control). Taken together, modifications of current cultivation systems toward using organic manure, that emit less CO2, could effectively mitigate CO2 impacts regardless of the selected water management practice.