Rb. Matthews et al., Using a crop/soil simulation model and GIS techniques to assess methane emissions from rice fields in Asia. IV. Upscaling to national levels, NUTR CYCL A, 58(1-3), 2000, pp. 201-217
The process-based crop/soil model MERES (Methane Emissions from Rice EcoSys
tems) was used together with daily weather data, spatial soil data, and ric
e-growing statistics to estimate the annual methane (CH4) emissions from Ch
ina, India, Indonesia, Philippines, and Thailand under various crop managem
ent scenarios. Four crop management scenarios were considered: (a) a 'basel
ine' scenario assuming no addition of organic amendments or field drainage
during the growing season, (b) addition of 3,000 kg DM ha(-1) of green manu
re at the start of the season but no field drainage, (c) no organic amendme
nts but drainage of the field for a 14-d period in the middle of the season
and again at the end of the season, and (d) addition of 3,000 kg DM ha(-1)
of green manure and field drainage in the middle and end of the season. Fo
r each scenario, simulations were made at each location for irrigated and r
ainfed rice ecosystems in the main rice-growing season, and for irrigated r
ice in the second (or 'dry') season. Overall annual emissions (Tg CH4 yr(-1
)) for a province/district were calculated by multiplying the rates of CH4
emission (kg CH4 ha(-1) yr(-1)) by the area of rice grown in each ecosystem
and in each season obtained from the Huke and Huke (1997) database of rice
production. Using the baseline scenario, annual CH4 emissions for China, I
ndia, Indonesia, Philippines, and Thailand were calculated to be 3.73, 2.14
, 1.65, 0.14, and 0.18 Tg CH4 yr(-1), respectively. Addition of 3,000 kg DM
ha(-1) green manure at the start of the season increased emissions by an a
verage of 128% across the five countries, with a range of 74-259%. Drainage
of the field in the middle and at the end of the season reduced emissions
by an average of 13% across the five countries, with a range of -10% to -39
%. The combination of organic amendments and field drainage resulted in an
increase in emissions by an average of 86% across the five countries, with
a range of 15-176%. The sum of CH4 emissions from these five countries, com
prising about 70% of the global rice area, ranged from 6.49 to 17.42 Tg CH4
yr(-1), depending on the crop management scenario.