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

e increased during times of flooding and slowly decrease when drained (Mitsuchi, 1974). There
will however be a trade-off when considering the possibilities of denitrification and emissions of
N2O. Intermittent flooding showed a 17% lower GWP for N2O and CH4 than continuous flooding in
China (Yue et al., 2005) and thus the most favorable would seem to go for a fluctuating water table
as with SRI.
The emissions of N2O are quite large during the dry season – up to three to four times larger than
upon the growth season (Dobermann & Fairhurst, 2000) upon aerobic conditions. Denitrification is
occurring in situations of lack of oxygen and some bacterial strains will then use nitrate as a source
of respiration in stead of oxygen (Patrick & Reddy, 1976). Denitrification can especially occur in
wetland soils, poorly drained soils and soils fertilized with nitrate (Borggaard & Elberling, 2003).
The theoretical SRI will give fewer rises to denitrification due to the fluctuating water table. The
SRI practiced by farmers seems though however to experience some periods with denitrification
due to the long drought periods and aerobic conditions.
The farmers in Prey Veng do however not possess the means to control water, they are able to drain
their fields but not adjust water levels later on. It is therefore very risky if they drain at one point
and not are able to adjust water if a prolonged drought is present. Only 3% of the target farmers use
less water, and their fields might in theory build up less C than fields that are flooded according to
the findings of Mitsuchi (1974) but it is though doubtful if there will be any significant difference
between their C levels and the other participating farmers. Especially when considering that one
rice season is very short – a few months followed by a fallow period throughout the rest of the year.
The farmers who are able to adjust water levels (3%) will though be able to reduce CH4 emissions
due to drainage periods resulting in aerobic conditions (Wassmann et al., 2000; Yue et al., 2005;
Zou et al., 2005; Li et al., (2009) but will at the same time increase emissions of N2O and CO2 and
thereby creating a trade-off. The success of the drainage concepts is though depending on the
degree of drainage i.e. complete drainage or as in the SRI theories soil is kept moist/wet to dry
depending on the farmer and the area. If the soil is just a little too wet/moist there will still be
methane emissions due to anaerobic conditions.
The majority of farmers do as mentioned not adjust water levels and their “SRI” fields will emit
more CH4 but less N2O and CO2 due to long periods with anaerobic conditions. The question is then
which systems are to be preferred considering the present trade-off. Since few farmers use chemical
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