The major soils under lowland rice cultivation range from
loamy clay to clay soils. Lowland rice fields
are located in inland valley swamps, riverine floodplains and old
floodplains. These soils are relatively
higher in organic matter content and are more fertile than the upland soils. Area under lowland cultivation constitutes 52
% of the total cultivated area of The Gambia.
Research Objectives and Hypotheses
The
research objectives are as follows:
1.
To identify to
best rice seedling age for transplanting
2.
To find out if
SRI management practice is superior to conventional management practice
3.
To find out if
the current fertilizer recommended rate for The Gambia, meets the nutrient
demand of SRI production
4.
To promote SRI
management practices on-farm
The
research hypotheses are as follows:
1.
Transplanting is
best with younger seedlings
2.
SRI will increase
rice yields because the SRI management practices are superior
to
conventional ones
3.
Rice yield can be
increased with SRI using the current
fertilizer
recommendations in The Gambia
The
field experiments were conducted during the wet seasons of 2000, 2001 and
2002. They were conducted at the Gambia
National Agricultural Research Institute’s irrigated rice experimentation
fields and at the Integrated Rice Development Project tidal irrigation site in
Sapu,
I.
Diagnosing seedling growth rate and seedling quality
Two
rice varieties IET 3137 and ITA 306 were used.
Both of these varieties are widely grown in The Gambia and in
A
seedling nursery of the 2 varieties was prepared in August 2002, and 10
seedlings per variety were uprooted at 3, 7, 14, and 21 days intervals after
emergence. The number of leaves were
counted, and the seedling height measured.
The roots of the seedling are then removed with a pair of scissors, and
then placed in a jar of water for 7 days.
The number of new roots re-growth is counted and bulk root length
measured. The seedlings are then sun
dried for a week and average seedling dry matter is recorded. The trial was conducted during the wet season
of 2000.
II.
Effect of seedling age at transplanting under SRI management practice
Three
sets of rice nurseries were prepared at different intervals to produce
seedlings of 5, 10, and 35 days of age at time of transplanting. Seedlings of different ages were transplanted
on the same day in a split-plot design trial with 3 replications. Seedling age was the main plot, and variety
was the sub-plot. Two rice varieties
were tested, IET 3137, and ITA 306.
Seedlings
were transplanted in plot sizes of 3 x 5 m, at plant spacing of 30 x 30
cm. Water control and weeding were done
according to SRI management recommendations.
Fertilizer was applied at a rate of 70-30-30 kg/ha NPK, of which
30-30-30 kg/ha NPK was applied as basal, and 20 kg/ha N was applied at
tillering and again at panicle initiation growth stages. The trial was conducted in the wet season of
2002.
III.
SRI vs. conventional management practices
The
effect of three plant population densities and SRI management on rice grain
yield was investigated in 2000 wet season.
The planting distances between hills were as follows:
20 X 20 cm
30 x 30 cm
40 x 40 cm
Two
sets of rice nurseries were prepared at different intervals to produce
seedlings of 10 and 35 days of age at time of transplanting. Two types of management practices were used:
SRI and research recommended local management practices. The trial design was a split-split-plot. The main plot was the management practice,
the sub-plot was spacing, and the sub-sub-plot was variety. Two varieties, locally cultivated by farmers
in The Gambia; IET 3137 and ITA 306 were used.
Seedlings of different ages were transplanted on the same day in a
split-split-plot design trial with 3 replications. Seedling age was the main plot, and variety
was the sub-plot. Two rice varieties
were tested, IET 3137, and ITA 306.
Water
control and weeding were done according to SRI management recommendations in
the SRI main plot, and in the other farmer management practice was used. Fertilizer was applied in both blocks at a
rate of 70-30-30 kg/ha NPK, of which 30-30-30 kg/ha NPK was applied as basal,
and 20 kg/ha N was applied at tillering and again at panicle initiation growth
stages.
IV.
SRI with different fertilizer application rates
This
fertilizer trial with SRI management was conducted in 2001 and 2002 wet
seasons. Different fertilizer application
rates were tested with SRI management practice.
The components of SRI used were as follows:
30 x 30 cm spacing
Repeated wetting and drying
1-week-old seedlings (2-3 leaf stage)
Three
fertilizer application rates were investigated:
1.
70-30-30 NPK
kg/ha
2. High: 140-30-30 NPK kg/ha
3. Very High: 280-30-30 NPK kg/ha
Two
rice varieties, IET 3137 and ITA 306 were used in the trial. The trial was a split-plot design with 4
replications. The main plot was
fertilizer application rate. Bunds, 15
cm high, were constructed between the main plots to restrict inter-flow of
water and nutrients between the main plots.
The sub-plots were the varieties.
Plot sizes were 3 m wide and 5 m long.
Fertilizer
was applied as basal and topdressing at tillering and panicle initiation. The 70-30-30 kg/ha NPK was applied as
follows: 30-30-30 kg/ha NPK as basal, and 20 kg/ha N topdressing twice.
The
140-30-30 kg/ha NPK was applied as follows: 60-30-30 kg/ha NPK as basal, and 40
kg/ha N topdressing twice.
The
280-30-30 kg/ha NPK was applied as follows: 120-30-30 kg/ha NPK as basal, and
80 kg/ha N topdressing twice.
V.
SRI with compost and different urea topdressing rates
This
trial was conducted in the wet season of 2002.
SRI management practice was tested with compost and urea
application. Compost made out of rice
straw, rice husk and farm-yard manure was applied at a rate of 5 t/ha. This provided approximately 60 kg/ha N. The fertilizer application rates were as
follow: Compost alone
Compost with 40 kg/ha N topdressing from urea 46% N
Compost with 80 kg/ha N topdressing from urea 46% N
70-30-30 kg/ha NPK without compost from urea 46% N
The
amounts of N topdressing rates were based on the amount usually applied by
farmers. The components of SRI used were
30 x 30 cm spacing, repeated wetting and drying, and 1-week-old seedlings (2-3
leaf stage).
Two
rice varieties, IET 3137 and ITA 306 were used in the trial. The trial was a split-plot design with 3
replications. The main plot was
fertilizer application rate. Bunds, 15
cm high, were constructed between the main plots. The two varieties were transplanted in the
sub-plots. Plot sizes were 3 m wide and
5 m long. Urea topdressing was applied
50 % at tillering and 50 % at panicle initiation.
VI.
On-Farm SRI management trials
The on-farm trial was conducted in 2001. It was a researcher managed. Ten
dabadas (households: the smallest divisible unit of a farm community in the
Each farmer did an SRI and their standard method of
production.
A standard variety IET 3137 was supplied to all participating
farmers. Ten days old seedlings are
transplanted at 30 x 30 cm spacing. Fertilizer
was applied at a rate of 70-30-30 NPK kg/ha which is the national recommended
rate, 30-30-30 kg/ha NPK was applied as
basal, and 20 kg/ha N was applied at tillering and panicle initiation growth
stages.
The standard practice is continuously flooded. The SRI practice is intermittently flooded
and dried. It is irrigated with enough
water to saturate the soil, and is re-irrigated after 2 or 3 days or until the
soil starts to show signs of slight water deficit.
Rice Varieties used in the trial:
ITA 306 was introduced by the International Institute of
Tropical Agriculture (IITA) in
IET 3137 is an introduction from
BG 90-2 is an introduction from
Land Preparation: The trial plot sizes were 3 x 5m. Primary land preparation was with a harrow
plow drawn by a 4-wheel tractor, and secondary land preparation was with a
2-wheel power-tiller. Leveling was done
with a power-tiller drawn leveling board and by hand shifting of soil. All plots were transplanted.
Weed control: In all trial inter-row weed control was
carried out mechanically with a roto-weeder, and intra-row weeding was by hand, at 14, 28 and 48
days after transplanting. No herbicide,
insecticide, or chemical disease control measures were used.