Effect of spacing and thinning date on the yield of broadcast nakati

136 C.K. SSEKABEMBE & T. L. ODONG
200,000 plants ha -1 ) for row-planted nakati, but it is not
clear what variety <strong>of</strong> nakati suits this <strong>spacing</strong>. Moreover,
most small-seeded crops like nakati, sesame <strong>and</strong> finger
millet are usually sown by broadcasting (Dunbar, 1969;
Jameson, 1970; Acl<strong>and</strong>, 1971; Tenywa et al., 1999). In
general, farmers in central Ug<strong>and</strong>a establish nakati using
the broadcasting method. However, after broadcasting the
crop is rarely thinned yet <strong>thinning</strong> has been shown to
improve yields in many crops particularly when it is done
properly <strong>and</strong> timely. For example, in sorghum, <strong>thinning</strong>
within two weeks after emergence (establishment)
produced the highest grain yield partly through production
<strong>of</strong> more viable tillers (heads per plant) <strong>and</strong> a higher leaf
area per plant (Busasi, 1980). In a previous survey in central
Ug<strong>and</strong>a, poor agronomic practices (like failure to attain an
optimum plant population) was identified as one <strong>of</strong> the
major production constraints for nakati (Ssekabembe et
al., 2003a). Therefore, the objective <strong>of</strong> the present study
on this ‘orphan crop’ was to determine its optimum plant
population (plant density) <strong>and</strong> <strong>thinning</strong> time when grown
as a broadcast crop.
Materials <strong>and</strong> methods
The study was carried out in four villages (Manyangwa,
Buwagga, Nakwelo, <strong>and</strong> Busukuma) near Makerere
University Agricultural Research Institute, Kabanyolo
(MUARIK) (0 o 28’N, 32 o 37’E), which is 17 km northeast
<strong>of</strong> Kampala in Wakiso district. Kabanyolo is also the
nearest meteorological station, <strong>and</strong> lies at an average
altitude <strong>of</strong> 1200 m. Most <strong>of</strong> the soils in the area are Oxisols,
which are highly weathered <strong>and</strong> low in soil fertility
although they may be deep <strong>and</strong> well drained. The l<strong>and</strong> at
the particular experimental sites had been rested from
continuous cropping for at least two growing seasons.
The mean daily maximum <strong>and</strong> minimum temperature <strong>of</strong> the
area are about 27 <strong>and</strong> 17 o C, respectively. The annual
average rainfall is about 1300 mm but its reliability
fluctuates a lot in the recent past. It is bimodal in
distribution with April <strong>and</strong> November as the usual wettest
months.
At each experimental site, the l<strong>and</strong> was prepared into a
fine seedbed by the farmers from whom the l<strong>and</strong> was rented.
Locally available seed from one farmer who saved it was
used in the study. Planting at all the sites was done by
one experienced nakati farmer. A liberal amount <strong>of</strong> nakati
seed was mixed with ash before broadcasting the seed
uniformly at each site. The treatments were <strong>thinning</strong> the
crop to a <strong>spacing</strong> <strong>of</strong> approximately 5, 10, 15 <strong>and</strong> 20 cm
(about 4,000,000; 1,000,000; 500,000 <strong>and</strong> 250,000 plants
ha -1 , respectively) in all possible directions <strong>of</strong> the
broadcast crop. The various <strong>spacing</strong>s were determined
using sticks with the predetermined length corresponding
to the various <strong>spacing</strong>s. In other words, with the fairly
high st<strong>and</strong> <strong>of</strong> the broadcast crop, <strong>thinning</strong> was done to
achieve the required plant populations <strong>of</strong> about 400, 100,
50 <strong>and</strong> 25 plants m -2 in each case at either 2, 3, or 4 weeks
after crop emergence. The unthinned crop had about 700-
800 nakati plants m -2 . In addition to these treatments, there
was no <strong>thinning</strong> at all <strong>of</strong> the broadcast crop, <strong>and</strong> ‘setting’.
‘Setting’ involves harvesting nakati plants as <strong>and</strong> when
they mature, leaving the young plants to grow <strong>and</strong> mature
as well (Ssekabembe et al., 2003a). Essentially, ‘setting’ is
piece meal harvesting. However, in this study this treatment
involved harvesting only twice; first when the majority <strong>of</strong>
plants were mature (when other treatments were harvested
8 weeks after planting) <strong>and</strong> when the remaining small <strong>and</strong>
young plants were given additional 2 weeks to mature. No
<strong>thinning</strong> <strong>and</strong> ‘setting’ constitute the usual farmers’ practice
in nakati production in central Ug<strong>and</strong>a. The treatments
were arranged in factorial combinations, <strong>and</strong> were laid out
in a r<strong>and</strong>omized complete block design with four replicates.
Each replicate was planted in a separate farm in the different
villages near Kabanyolo. The experiment was planted in
both the first <strong>and</strong> second rains <strong>of</strong> the same year using the
same plots. Each plot measured 3 x 4 m but sampling for
dry matter (yield) determination was restricted to the
middle 2 m 2 . The plots were weeded regularly by h<strong>and</strong>
pulling the weeds, to keep them relatively weed free. Each
plot received 120 g <strong>of</strong> NPK (17:17:17), which is equivalent
to 100 kg ha -1 , after <strong>thinning</strong> the crop. Insect pests <strong>and</strong>
diseases were controlled by spraying the crop with
Dimethoate (40 mls in 15 litres <strong>of</strong> water) <strong>and</strong> Dithane M 45
(50 g in 15 litres <strong>of</strong> water), respectively. This was done
three times during the crop growing season.
The experimental measurements included average
canopy height, which was measured in five different
positions in each plot, from the ground level to the top <strong>of</strong>
the plants where a horizontal bar was laid out in each
case. For simplicity, leaf area was estimated by taking linear
measurements on the top four leaves in the canopy <strong>of</strong> 5
plants in each plot, counting the total number <strong>of</strong> leaves
per plant <strong>and</strong> then multiplying by a factor <strong>of</strong> 0.71, which
was determined using a graph paper (Kemp, 1963). This
procedure has been similarly used in another study
(Ssekabembe, 1983). Dry matter (DM) was partitioned into
the edible portion consisting <strong>of</strong> the leaves <strong>and</strong> s<strong>of</strong>t parts
<strong>of</strong> the stem at the top <strong>of</strong> the plants, <strong>and</strong> the ‘reject’ portion
which consisted <strong>of</strong> the fibrous part <strong>of</strong> the stems <strong>and</strong> the
recoverable roots. Dry mater was obtained from a 2 m 2
sampling area in each plot, by drying the fresh 2 kg sub
samples in an oven at about 70 o C until constant dry weight
was attained. The DM yield was then calculated after
obtaining the moisture content <strong>of</strong> the fresh samples. A
similar procedure has been used by other workers such as
Ssekabembe & Sabiiti (1997) <strong>and</strong> Maheswarappa &
Nanjappa (2000). The DM yield was then converted to
yield per hectare. Data were subjected to analysis <strong>of</strong>
variance, <strong>and</strong> the significant level used was P=0.05.
Farmers’ practice <strong>of</strong> no <strong>thinning</strong> <strong>and</strong> setting was compared
with the <strong>thinning</strong> x <strong>spacing</strong> combinations using orthogonal
contrasts.
Results <strong>and</strong> discussion
<strong>Effect</strong> <strong>of</strong> <strong>thinning</strong> on edible yield per nakati plant. The
trend <strong>of</strong> DM yield <strong>of</strong> nakati in the two growing seasons
was similar. Therefore, the means <strong>of</strong> yield are reported
(Table 1). Comparison <strong>of</strong> the mean yield <strong>of</strong> nakati from the
growers’ practice (no <strong>thinning</strong> <strong>and</strong> ‘setting’) with the