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

2006). Hence both nutrient uptake is higher and competition due to nutrients is lower than in a
traditional field with 5-6 seedlings per hill. Normally the narrow spacing of transplants in
conventional fields will produce fewer tillers app. 8-13 per plant (Stoop et al., 2002), although this
will depend on soil and management practices and the used varieties. However for the conditions in
Cambodia it was observed that traditional fields often had a little more than 10 tillers per plant
whereas SRI plants often had a few more tillers. It is however notable here that most farmers did
not transplant younger seedlings to their SRI fields (1 farmer mentioned he used younger
seedlings). It is then remarkable that the difference in yields is more than 1 t. If farmers used
younger seedlings the difference in yield could have related to uprooting damage from the seedbed
as younger seedlings will be less damaged by uprooting upon transplanting (Yoshida, 1981). Young
seedlings used in SRI are also believed to be more easily adapting to the new environments found in
the field and the “stress” involved in transplanting (Kabir, 2006).
The competition between the plants might have an effect on the yield potential – also called
intraspecific competition which is competition between plants of the same species and is very much
depending on density (Antonovics & Levin, 1980). Kawano et al. (1974) state that in soils low in N
content, rice plants will first compete for the soil Nitrogen and later light which is vice versa in soils
high in N content. Kawano et al. (1974) further conclude from trials in Peru on spacing and
intraspecific competition involving 25 different varieties that in soils low in N content, wider
spacing is beneficial which especially is suitable for vigorous tall growing varieties with long
growth duration. With the given low N containing soils in Prey Veng, the wider spacing might thus
have caused a yield increase in the SRI field as compared to the traditional fields.
The competition from weeds could not have caused the differences in yield as weed problems are
low in the traditional systems due to dense spacing and in the SRI fields hand weeding was done
regularly by most farmers. Koma (2007) states that farmers can obtain higher yields with SRI, even
if they only manage some of the concepts.
Given these yield increases is also one of the reasons why farmers would like to continue with SRI
for the next season. Figure 15 pictures main reasons why farmers would like to continue with SRI
next year. However, when farmers were interviewed, only one household had harvested and the
farmers could therefore not have experienced the increase in yield. This illustrates how confident
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