[CH4 and N2O emission from a winter-time flooded paddy field in a hilly area of Southwest China].

By the method of static opaque chamber/modified gas chromatography, a one-year field experiment was conducted to measure in situ the CH4 and N2O emission from a winter-time flooded paddy field in a hilly area of Southwest China. Gas samples were taken simultaneously from rice-involved and rice-uninvolved plots. The results showed that during rice growth period, the CH4 emission from the winter-time flooded paddy field was higher than that from other paddy fields, but largely lower than many previous reports for the similar regions in Southwest China. The average flux of CH4 emission from rice-involved plots was 22.76 +/- 2.76 mg CH4 x m(-2) x h(-1) during rice growth period, 9.64 +/- 1.17 mg CH4 x m(-2) x h(-1) per year, and 1.43 +/- 0.20 mg CH4 x m(-2) x h(-1) during non-rice growth season; while that from rice-uninvolved plots was only 2.03 +/- 0.18 mg CH4 x m(-2) x h(-1) per year, markedly lower than those from rice-involved plots. During rice growth season, the mean emission rate of CH4 and N2O was 4.53 +/- 0.38 mg CH4 x m(-2) x h(-1) and 32.01 +/- 5.02 microg N2O x m(-2) x h(-1) from rice-uninvolved plots, but reached to 22.76 +/- 2.76 mg CH4 x m(-2) x h(-1) and 73.04 +/- 5.03 microg N2O x m(-2) x h(-1) from rice-involved plots, respectively. Rice involvement resulted in 302% increment of CH4 and 128% increment of N2O emission. There was a clear trade-off between CH4 and N2O emission in paddy fields. Even with a span of 500 years, our calculation showed that in this winter-time flooded paddy field, the GWP contributed by N2O production was 7.9% of the CH4 contribution, and thus, the greenhouse effect of N2O production from this field was very small.