Results
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.
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.