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

Table 8. An estimated picture of an annual nutrient budget for the target farmers. All nutrient values are in
kg/ha. Kundu & Ladha (1999) refer to Koyama (1981) stating that upon applying organic materials 10-20% of
the N is mineralized and thus plant available, and the rest is immobilised and lost. An average value of 15%
mineralized N, P and K has been chosen. Nutrient inputs from sediments have not been included as no natural
flooding occurred in the target area.
N P K
Input
(Kg/ha) (Kg/ha) (Kg/ha) Specifications References
Precipitation 12 0,2 12 Greenland (1997)
Biological N fixation (BNF): mainly
Azolla 30
Dobermann & Fairhurst (2000)
Seedling uptakes estimated to be 2% of straw of
Transplanted seedlings (30 days)
0,6 0,08 1,4
5.25 t/ha. Uptake rates determined from De Datta
(1987)
N (1,67%), P (0,83%) and K (1,66%) of the
Compost incl. GM 50 25 49,8 3t/ha
compost estimated from Latif et al. (2005)
Total 92,6 25,28 63,2
Output
Grain 38 7 11 3,5 t/ha grain yield Uptake rates estimated from De Datta (1987)
Straw 26,6 3,8 67,5
Leaching (percolation)
Gaseous loss: Volatalization &
20 1 10
denitrification 4
Total 88,6 11,8 88,5
Net balance 4 13,48 - 25,3
5,25t/ha dry
weight
Harvest Index 0,5 estimated from Dobermann &
Fairhurst (2000). 5% from stubble not removed.
Uptake rates estimated from De Datta (1987)
Estimated from Dobermann & Fairhurst (2000) and
N loss from leaching George et al. (1992)
Estimated from Greenland (1997)
9.6. Can SRI mitigate GHGs and at the same time increase soil quality
through C sequestration?
There are large differences between the theoretical concepts of SRI as described by Laulanie
(1993), Stoop et al. (2002) and Sheehy et al. (2004) and the SRI conducted by the farmers in the
target area of this study. This section will try to evaluate the consequences of the conceptual SRI
and the SRI conducted by the farmers in Prey Veng.
Table 10 is a theoretical model illustrating how a theoretical SRI system as described by Stoop et al.
(2002) and Sheehy et al. (2004) and the SRI practiced by farmers potentially will affect emissions
of CH4, N2O and CO2 and influence the soil C pool.
The use of a fluctuating water table resulting in periods of drainage and moist soils (Laulanie, 1993;
Sheehy et al. 2004) will result in long periods with aerobic conditions reducing CH4, which though
will lead to increased emissions of N2O but at the same time increase C content. SOM will therefore
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