Carbon dioxide flux density in cultivated rice paddy field

The carbon dioxide flux density in a subtropical cultivated rice paddy field were determined over four crop seasons (two consecutive years) at five stages of rice plant development, transplanting, active tillering, booting, flowering and ripening, and an idle period between crops. During 24 h sampling periods at those stages, the CO2 flux densities were measured and found to be -2,000 to 55,000 mg CO2/m2/day in the first year and 600 to 29,000 mg CO2/m2/day in the second year in acrylic chambers covering rice plants. The CO2 flux densities in glass domes without plants but with soil were -700 to 6,000 mg CO2/m2/day in the first year and 147 to 4,500 mg CO2/m2/day in the second year. The data for the CO2 flux density over an entire year are extrapolated. Although our non-controlled environment experiments have inherent drawbacks, the collected data indicate that continuous rice cultivation has a tendency to result in increased CO2 emissions.