Methane emission from rice fields in Mainland China: Amount, seasonal and spatial distribution

Xiaoyuan Yan, Toshimasa Ohara, Hajime Akimoto, Zucong Cai

Journal of Geophysical Research, 108(D16), 4505, doi:10.1029/2002JD003182, 2003.


China is the largest rice producer in the world. Methane (CH4) emission from its rice fields has been widely measured since the late 1980s. In this study, we collected results of most of the field studies available so far, which constitutes 204 season-treatment measurements conducted on 23 sites. Analysis of these data shows that input of organic materials such as green manure, animal waste, and crop straw increases CH4 emission by a factor of 2; average CH4 flux from intermittently irrigated rice fields is 53% of that from continuously flooded rice field; and average CH4 emission flux from late rice fields is 1.6 and 2.3 times those from early and single rice fields. There is regional difference in emission factors, with a decreasing trend from south to north. We assume half of the rice fields in China received organic input by referring to earlier estimates of CH4 emission from Chinese rice fields and some recent reports on the use of crop residue and green manure. From the frequency of various water managements in the survey field experiments and statements in individual reports, we expect that two-thirds of the irrigated rice fields were intermittently flooded. Based on these assumptions and the region-specific emission factors and statistical data on rice area of 1995, we estimated CH4 emission from rice fields during rice-growing season (from transplanting to harvest) in Mainland China to be 7.67 Tg yr-1, with a range of 5.82 to 9.57 Tg CH4 yr-1 due to the uncertainties in the assumption on rice area receiving organic input and under intermittent irrigation. A generalized seasonal flux pattern was developed separately for early, late and single rice. Monthly distribution of the annual emission was estimated from rice calendar and these flux patterns, showed that highest emission occurs in August. Hot spots of emission are the plains of Dongting Lake in Hunan province, Boyang Lake in Jiangxi province, the delta region of Qiantang River in Zhejiang province and Sichuan Basin. Nearly 90% of the emission occurs between 23-33º N.