SRI management practices produced higher yields than the
currently recommended management practices in The Gambia. Yields using SRI management practices are 2
to 3 times higher than national averages in The Gambia and the
Younger seedlings are more viable than older ones when uprooted and transplanted. Although older seedlings have a relatively higher bulk root density, they also have a relatively much higher above-ground biomass to supply nutrient and water. With SRI management in The Gambia 5 and 10 day old seedlings gave similar results. The 10 day old seedlings were relatively easier to handle. At 10 day old the seedlings will not have reached their fourth phyllochron of growth, the time when the plant begins to tiller.
Except for plant height and tiller ability, no significant varietal effect was seen. Overall, water management practice did have an effect on plant height. A larger number of tillers per hill was not associated with repeated wetting and drying, as occurred in response to wider spacing.
An increase in SRI yields in subsequent years was observed. Yields in 2002 were higher than in 2001 by 42 % on average for the SRI fertilizer trial (6.2 t/ha and 9.5 t/ha respectively). This was probably due to improved soil conditions following 2001 crop, as a result of residual fertilizer and stover incorporation.
Application of compost with 80 kg/ha N as a topdressing gave better yields than compost alone, but was not significantly different from compost with 40 kg/ha N topdressing. In SRI management nitrogen is gradually released from decomposing organic matter during the growing season, so less N fertilization is required as soil organic matter levels increase. A continuously flooded rice field requires more N fertilizer than one that is repeatedly wetted and dried.
Under SRI management practice, the availability of nutrients to support high yields did not seem to be limiting in the soils where the trials were conducted. This may be due to the fact that the rate of mineralization is enhanced by the process of repeated wetting and drying and the enhanced development of microbial populations in the soil.
SRI water control acts a preventive measure against defoliator caseworm (Nymphula stagnalis) outbreak. The caseworms feeds on the rice leaves and in the process some part of the leaves fall in the water. A field infested with caseworms is easily detected by the large number of leaves floating in the water. Caseworms are semi-aquatic and move from one plant to another by swimming in the flood waters or floating on top of rice leaves in water. Draining the field restricts caseworm movement, thereby limiting their spread. Keeping a field drained for 3 days is enough to starve and eliminate any caseworm present.
rice field in Sapu, The Gambia was infested by caseworms resulting in
extremely low plant stand count
Momodou Conteh’s rice field in Sapu, The Gambia was infested by caseworms resulting in extremely low plant stand count
Caseworm laying eggs on a rice plant
The SRI water management practices of repeated soil wetting and drying were also found to be beneficial to rice plant growth probably through increased biological nitrogen fixation, more nutrient availability, profuse root development, increased tillering, and a high panicle setting ratio leading to higher grain yields.