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

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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
Spacing <strong>and</strong> <strong>thinning</strong> <strong>date</strong> on the yield <strong>of</strong> broadcast nakati 137 Table 1. Comparison <strong>of</strong> nakati yield from ‘setting’ <strong>and</strong> no <strong>thinning</strong>, <strong>and</strong> that from various <strong>thinning</strong> <strong>date</strong>s x <strong>spacing</strong> treatment combinations in central Ug<strong>and</strong>a. Treatments Edible portion Edible portion Reject portion Reject portion Canopy height plant -1 (g) (kg ha -1 ) plant -1 (g) (kg ha -1 ) (cm) Setting 4.89 1174 9.2 1919 37.2 No <strong>thinning</strong> 5.05 1164 8.2 1932 36.0 Mean 4.97 1169 8.7 1926 36.6 Thinning <strong>date</strong> * (weeks) x <strong>spacing</strong> (cm) 2; 5 x 5 8.30 1403 14.5 1267 38.9 2; 10 x 10 11.41 1295 14.8 1484 34.1 2; 15 x 15 15.24 1101 21.0 1474 32.4 2; 20 x 20 23.73 1230 28.5 1506 34.5 3; 5 x 5 10.89 1190 16.4 1722 38.1 3; 10 x 10 12.55 997 17.2 1300 31.9 3; 15 x 15 21.71 1260 17.2 1698 39.3 3; 20 x 20 25.36 1043 34.9 1199 33.1 4; 5 x 5 9.43 1274 16.5 1782 37.3 4; 10 x 10 13.22 1042 18.7 1415 32.9 4; 15 x 15 14.55 1006 16.7 1050 32.0 4; 20 x 20 30.95 1151 38.5 1216 31.4 Mean 16.45 1166 21.2 1484 34.7 S.E.D 4.88 171.3 9.31 340.5 5.0 * Weeks after emergence <strong>of</strong> nakati x <strong>spacing</strong> treatment combinations. <strong>thinning</strong> x <strong>spacing</strong> treatment combinations showed that the former practices resulted in significantly lower edible yield per nakati plant (P
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Effect of spacing and thinning date on the yield of broadcast nakati

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