Carbon Dioxide Flux from Rice Paddy Soils in Central China: Effects of Intermittent Flooding and Draining Cycles

A field experiment was conducted to (i) examine the diurnal and seasonal soil carbon dioxide (CO(2)) fluxes pattern in rice paddy fields in central China and (ii) assess the role of floodwater in controlling the emissions of CO(2) from soil and floodwater in intermittently draining rice paddy soil. The soil CO(2) flux rates ranged from -0.45 to 8.62 µmol.m(-2).s(-1) during the rice-growing season. The net effluxes of CO(2) from the paddy soil were lower when the paddy was flooded than when it was drained. The CO(2) emissions for the drained conditions showed distinct diurnal variation with a maximum efflux observed in the afternoon. When the paddy was flooded, daytime soil CO(2) fluxes reversed with a peak negative efflux just after midday. In draining/flooding alternating periods, a sudden pulse-like event of rapidly increasing CO(2) efflux occured in response to re-flooding after draining. Correlation analysis showed a negative relation between soil CO(2) flux and temperature under flooded conditions, but a positive relation was found under drained conditions. The results showed that draining and flooding cycles play a vital role in controlling CO(2) emissions from paddy soils.