Wednesday, November 15, 2006

Effect of Change in Land Use from Paddy Rice to Upland Crop Cultivation on Methane and Nitrous Oxide Emissions.

Seiichi Nishimura1, Takuji Sawamoto2, Hiroko Akiyama3, Shigeto Sudo3, and Kazuyuki Yagi3. (1) JAPAN, Government of, Natl Inst. for Agro-Env. Sci., 3-1-3 Kannondai Tsukuba, Ibaraki, 305-8604, JAPAN, (2) Rakuno Gakuen University, 582 Midori-cho, Bunkyodai, Ebetsu, 069-8501, Japan, (3) Natl Inst. for Agro-Env. Sci., 3-1-3 Kannondai, Tsukuba, 305-8604, Japan

Since rotation of paddy rice-upland crop cultivations is a major land use management widely conducted in Japan, effect of change in land use on greenhouse gas emissions from drained paddy fields are required to be clarified. In this study, methane (CH4) and nitrous oxide (N2O) emissions in both paddy fields (PR) and drained fields under upland crop cultivations (UR: single cropping of upland rice, SW: double cropping of soybean/wheat) were measured over two and a half years in the experimental fields with an automated flux monitoring system.

CH4 emission in the PR plots in 2003 was 5.8 times higher than that in 2002, mainly because of a prolonged period of continuous submergence in 2003. N2O emissions in the PR plots were low during the paddy rice cultivation periods.

In the UR and SW plots, CH4 emissions were stopped. On the other hand, significantly higher N2O emissions were often observed during the flowering to ripening stages of the cultivated upland crops, and other temporal increases in N2O fluxes were also occasionally found after heavy rainfall or crop harvesting. Cumulative N2O emissions in the UR and SW plots were three- to fivefold higher than that in the PR plots.

The combined net global warming potentials (net GWP) by the CH4 and N2O emissions were 100 to 442, 102 to 110, and 79 to 146 g CO2 m–2 in the PR, UR, and SW plots, respectively. Net GWP in the PR plots in 2003 was extremely high compared with the other values, owing to the high levels of CH4 emission.

These results suggest that drainage of paddy soils for upland crop cultivation is effective for reducing net GWP in paddy fields with high potential for CH4 emission, such as those that are poorly drained or have low soil iron content.

Handout (.pdf format, 419.0 kb)