Quantifying CO2, H2O, and CH4 fluxes over an intermittently- irrigated rice paddy

Rice is a major staple food for more than three billion people. However, growing rice consumes substantial amount of water and emits methane fluxes. In this study, we report 1.5 year observation of CO2, H2O and CH4 fluxes measured using an eddy covariance system in an intermittently-irrigated paddy rice in South Korea. On an annual scale (May 2015 through Apr 2016), the paddy rice site acted as CO2 sink (-168 gC m-2 yr-1) with 685 gC m-2 yr-1 and 517 gC m-2 yr-1 for GPP and Reco, respectively. Rice yield was 8.08 ton ha-1 which is two-fold of mean global rice yield. Annual CH4 emission was 15 gC m-2 yr-1, which is comparable to the other paddy rice sites in California, Japan, and India. CH4 emissions were dominant during daytime in irrigated period, and during nighttime in drained period. Annual evaporation was 585 mm yr-1, with rapid increase after irrigation. In 2016, irrigation and transplanting timings were two weeks earlier than 2015. However, the earlier activities did not lead earlier green-up. The timings of increase in GPP were almost identical between the two years, indicating that water loss via evaporation was unnecessarily made. The results highlight that an integrated management strategy is required to reduce CH4 emission, increase yield, and reduce evaporation loss.