Rice Yield Increase by the System of Rice Intensification is Dependent on Supplementary Water Availability in Rainfed Lowland Fields of Southern Cambodia

Increasing rice yield in rainfed fields is one of the major agricultural challenges in Cambodia. As an answer to this challenge, we focused on the System of Rice Intensification (SRI), which has been reported to increase rice yield while reducing water use, and has actually been adopted by many farmers. To elucidate how SRI can increase rice yield under water constraint in rainfed fields, we conducted an interview study with 106 farming households in Popel commune, Tram Kak District, Takeo Province of Cambodia in 2015, and asked them about the wet season rice in 2014. The farmers cultivated rice in total of 167 fields, of which 35 fields were under SRI practices whereas 132 fields were under conventional ones. We found that SRI was practiced more often in fields where supplementary water was available from ponds, rivers, and tube wells than those without it. In the former fields, SRI increased rice yield, whereas it did not in the latter fields. In SRI fields without supplementary water, younger seedlings planted earlier should have experienced severer water stress than those in conventional fields, and lost advantage of SRI to develop more tillers and thereby more grains. The dependency of yield increase by SRI on supplementary water availability implies that the prospect of rice yield increase via greater adoption of SRI would hinge on the capacity to increase supplementary water availability in the rainfed fields.