EFFECT OF THE SYSTEM OF RICE INTENSIFICATION (SRI) ON ...

are required (app. 150-200 mm) and farmers producing lowland rainfed rice are forced to wait app.
one to three months before there is enough water to puddle.
3.4 Drainage periods and GHG emissions
The effects of a changing water level in a rice field leading to anaerobic and aerobic conditions will
influence GHGs emissions and especially methane emissions. Wassmann et al., (2000) conducted
studies on CH4 emissions from five locations in Asia and discovered that soils amended with
organic manure had higher emissions of GHGs compared to soils fertilized with mineral fertilizers.
Intermittent flooding and mid season drainage resulted in lower emissions than with conditions of
continuous flooding (Wassmann et al., 2000). Emission rates ranged from less than 100 kg CH4
ha -1 to more than 400 kg CH4 ha -1 for intermittent irrigation and continuous flooding respectively
(Wassmann et al., 2000). Emissions were different within the different periods of the rice crop with
highest emissions during the reproductive stage and the highest temperatures (Wassmann et al.,
2000) which is also true for the other GHGs.
Drainage periods will lower CH4 but will however affect the emission rates of N2O. Yue et al.
(2005) compared continuous flooding with intermittent flooding and their role on CH4 and N2O
emissions in Southern China and found that intermittent flooding showed a 17% lower GWP
compared to continuous flooding while there was no significant differences between yields.
Methane emissions decreased but N2O increased with intermittent flooding but the trade-off was the
most optimum as compared to continuous flooding (Yue et al., 2005). Zou et al. (2005) found that
in Chinese rice fields with continuous flooding N2O emission rates was 0.03 mg m -2 d -1 as
compared to rice cropping with a mid season drainage of 14.1 mg m -2 d -1 . Both treatments received
2.25 t ha -1 of wheat straw. Mid season drainage periods are often used in China and Japan but not to
a large extent in warmer rice growing climates (Greenland, 1997). The effect of drainage in the
Cambodian climate, which is very different from the Chinese and Japanese climatic situation, might
result in different emission rates due to temperature and a faster decomposition of OM.
Water management involving mitigation interests or because of water shortages will have large
influences on emission rates of CH4, N2O and CO2 with many trade-offs involved (Frolking et al.,
2004). A farming system trying to involve mitigation of all three GHGs and involve and deal with
the trade-offs would be an optimal one. But which system can cope with such challenges and still
sustain the farmer and his family?
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