Determination of optimum sesame population in the finger millet + sesame additive intercropping system
Nakyagaba, Winfred N.
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Sesame (Sesamum indicum L.) and finger millet (Eleusine coracana) are important food security crops in Northern and Eastern Uganda, with the latter being established in most parts of the two regions. The two crop species are often grown as intercrops though finger millet is often considered to be the main crop. This study was designed to determine (i) the optimum sesame population that can be incorporated into pure finger millet stands without decreasing finger millet yield significantly. (ii) the response of the sesame + finger millet additive intercropping with and without NPK application. (iii) the overall biological productivity (based on LER) of the sesame + finger millet additive intercropping system. Field trials were conducted during the cropping seasons of 2005 (2005A and 2005B) in Tororo at the District Agricultural Training and Information Centre (DATIC) and for three seasons (2005A, 2005B, 2006A) in Soroti at the National Semi-Arid Resources Research Institute (NaSARRI). The treatments included five sesame plant populations additively intercropped into finger millet, and these were: 222,000, 111,000, 74,000, 55,000 and 44,000 plants ha-1. These were achieved by planting single rows of sesame midway of finger millet rows, to a spacing of 45 x 10 cm, 45 x 20 cm, 45 x 30 cm, 45 x 40 cm and 45 x 50 cm. Thus, the various sesame populations were attained by changing it’s within – the – row spacing. The second treatment was NPK fertiliser (25:5:5) applied at a rate of 200 kg ha-1 compared to the control. The treatments (the 5 combinations of intercrops and 2 sole crop treatments) were arranged in a randomised complete block design in a split plot and replicated four times. Results showed no significant interaction between sesame population and NPK application in terms of influencing finger millet and sesame dry matter (DM) and grain yield. However, there was a significant (P<0.05) effect of sesame population on finger millet leaf and stem DM production at Tororo DATIC only during 2005B. The highest finger millet leaf, stem and total DM was produced in pure finger millet stand (290,000 plants ha-1). The difference was up to 40% for finger millet leaf dry matter and 38% for finger millet stem DM. Pure finger millet stand produced higher mean total finger millet DM than the additive mixtures at both locations. The reduction in total finger millet DM production in additive mixtures was 26% and 20% for Tororo and Serere, respectively. Sesame DM production increased significantly (P<0.05) with increase in sesame plant population at both locations. The pure sesame stand had the highest dry matter. The difference between the pure stand and additive mixtures was 53% for sesame leaf DM and 51% for sesame stem DM in Tororo while in Serere it was 39% and 43% for sesame leaf and stem dry matter, respectively. The second season (2005B) supported significantly (P<0.05) higher amounts of sesame leaf, stem and total dry matter production than the first season at both locations. Application of NPK to the additive mixtures did not produce a significant (P<0.05) effect on finger millet and sesame leaf, stem and total DM production at Tororo and Serere during the two seasons of 2005A and 2005B. However, NPK application had a significant (P<0.05) effect on finger millet leaf and total dry matter production as well as sesame stem and total dry matter at Serere during 2006A. Application of NPK during 2006A significantly (P<0.05) increased finger millet leaf and total DM production by 35% and 38.3%, respectively while sesame stem and total dry matter production increased by 14.7% and 18.8%, respectively at Serere. The effect of sesame plant population on finger millet tiller production and finger millet Leaf Area Index (LAI) in the additive mixtures was not significant. However, sesame population had a significant effect on sesame LAI in additive mixtures which increased with increase in sesame population up to 111,000 plants ha-1. Sesame population had no significant (P<0.05) effect on finger millet yield and yield components at both locations and during all the seasons for low populations of sesame in the additive mixture. In other words the yield of finger millet was not significantly decreased when sesame was additively incorporated into finger millet in Tororo. Hence, the sesame yield obtained from the additive mixture was a bonus or additional benefit. For instance, at Serere, an average of 1,799kg ha-1 of finger millet and 151 kg ha-1 of sesame was obtained at a low sesame population of 55,000 sesame plants ha-1 (45 x 40 cm) in the additive mixture. This compares favourably with 800 kg ha-1 average obtained under Uganda conditions. The additive mixtures produced more finger millet yield with addition sesame bonus. However, at Serere, sesame population had a significant effect on sesame total yield (2005A and 2006A), number of capsules plant ha-1 (2005A) and on grain yield plant-1 during 2006A. In addition, there was a significant (P<0.05) increase associated with NPK application on mean heads ha-1, mean seed yield plant-1 and mean grain yield ha-1 at Serere. The associated increase was 15%, 15% and 17% respectively. The combined finger millet mean grain yield was 1542 and 1854 kg ha-1 without and with NPK application. Sesame grain yield was significantly higher with NPK application corresponding to 38% yield increase in 2005B. Total LER for mixtures was high and more than unity at almost all plant populations at both Tororo and Serere and in all seasons, indicating a yield advantage of intercropping over sole crops. The second season (2005B) produced higher total LER than the first season at both locations. The yield advantage was 58% and 74% at Tororo during 2005A and 2005B, respectively, and 30%, 73% and 13% at Serere during 2005A, 2005B and 2006A, respectively. Therefore, additive intercropping was advantageous at both sites. Finger millet had higher mean partial LER compared to sesame at both locations indicating that finger millet was more competitive than sesame. Overall, a higher mean total LER was observed at Tororo (1.7) than at Serere (1.4) indicating that a higher yield advantage was achieved at Tororo than Serere. At Tororo, the sesame plant population of 111,000 (45 x 20 cm) had the highest mean total LER (2.1) while 44,000 (45 x 50 cm) had the lowest mean total LER (1.3). Similarly, at Serere, the highest total LER (1.5) was obtained at a relatively low sesame plant population of 55,000 (45 x 40 cm) and the lowest LER (1.3) at 44,000 (45 x 50 cm) sesame plants ha-1. Using regression analysis, the optimum sesame population at Tororo was close to 111,000 plants ha-1 and 55,000 sesame plants ha-1 for Serere. The results indicate that on average, a population of 55,000 sesame plants ha-1 for Serere can be incorporated into pure finger millet stands without reducing finger millet yield significantly and yet get a mean bonus sesame yield of 151kg ha-1. On the other hand, application of NPK at a rate of 200kg ha-1 did not raise the yield of intercrops significantly and the potential of improved varieties was not realised. Failure of NPK to give a significant response was attributed to loss of the fertiliser through leaching, soil erosion and runoff rather than inherent failure of the crops to respond to NPK application. It is suggested that a specific study be conducted to assess the effect of different levels of NPK on sesame and finger millet. In summary the present study showed that finger millet and sesame additive intercropping gives good yield as long as a low population of sesame is imposed into sole finger millet. Sole finger millet could accommodate 55,000 sesame plants ha-1 without significantly reducing finger millet yield.