Effects of Irrigation Intervals for Paddy Rice Plants On Greenhouse Gas Fluxes (CO2, CH4 and N2O).

Effects of irrigation intervals for paddy rice plants on greenhouse gas fluxes (CO₂, CH₄ and N₂O).

Yusuke Kudo^* and Kosuke Noborio^*

Graduate School of Agriculture, Meiji University^*

Farmlands may be thought as emitting sources of greenhouse gases (GHGs) such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). Especially, mitigating GHG emissions in rice paddy fields may have a large impact in monsoon Asia, because 90% of world rice paddy fields are located in Asia including in Japan. Previous studies showed that CH₄ emission was reduced using intermittent irrigation alternatively repeating moistening and drying soil. However, transient drying soil by intermittent irrigation may emit more CO₂ and N₂O. In addition, each of three gases may be differently emitted by different irrigation interval scenarios. The purpose of this study was to investigate effects of irrigation intervals on GHG fluxes (CO₂, CH₄ and N₂O) in rice paddy fields. Rice plants are transplanted in six lysimeters (2×2×2 m) in Meiji University in central Japan. Three water management practices are used: (1) two-day drainage after one-day flooding, (2) four-day drainage after one-day flooding, and (3) continuous flooding except during the midseason drainage as the control practice. We measure the gas fluxes of CO₂, CH₄ and N₂O during growing season until harvest using the closed chamber method. Each gas concentration is analyzed with a GC equipped with FID and ECD. The accumulation of gas fluxes using global warming potential (GWP) for water management practice is compared and discussed.