Evaluation of elite groundnut varieties for response to plant density, intercropping and yield stability in Central Uganda
Sendikaddiwa, James Kajubi
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Groundnut (Arachis hypogaea. L.) is an important grain legume crop grown by resource poor farmers all over Uganda, for food and as a ready source of income. However, most groundnut varieties grown in Central Uganda are still local, traditional cultivars, typically low grain yielding, with poor agronomic characteristics and responding poorly to improved cultural practices for higher yield. Although superior genotypes have been developed at Research centres especially National Semi Arid Resources Research Institute (NaSARRI), Serere, since the 1990’s, their dissemination to resource poor farmers in rural areas has been ineffective. The purpose of this study, therefore, was to evaluate the performance of new elite groundnut varieties under different agronomic practices in two districts of central Uganda. The study was conducted to evaluate yield performance of improved groundnut varieties in comparison to a local test variety (Red beauty) in different planting patterns and environments. It was also conducted to establish the variety responses to intercropping with maize at different intercropping patterns and to establish varietal yield stability and adaptation to different environments. The specific objectives were to determine the most appropriate planting pattern that would maximize groundnut yield and to establish the effect of intercropping the elite groundnut varieties with maize using different intercropping patterns. The study was conducted in two districts (Wakiso and Mpigi) and in five locations namely; Kabanyolo in Nangabo sub-county, in Wakiso district, and Kyegonza 1, Kyegonza 2, Mweese and Bukinda in Mpigi district. Two experiments were conducted on-station at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) during the October, 2007 and March, 2008 rains. The first experiment investigated the effect of varying planting patterns on the yield performance of four elite groundnut varieties namely; Serenut 1, 2, 3, 4, and a local check variety, Red beauty. The treatments comprised of eight spacing patterns namely; 50x10cm, 50x20cm, 60x10cm, 60x20cm, 75x10cm, 75x20cm, 90x10cm and 90x20cm. These treatments were set up in a split-split plot of a randomized complete block design (RCBD) with three replications. The second experiment investigated the effect of intercropping the five groundnut varieties with maize. The experiment was laid out in a split plot design of a randomized complete block design (RCBD) where maize row spacing was varied at two levels; 100x30cm and 150x30cm giving rise to two inter-row and three inter-row treatments of groundnuts in between the maize lines. Data were collected on growth parameters namely; leaf area, leaf area index, leaf area ratio, number of branches and leaves, fresh and dry weight of leaves as well as stem length, fresh and dry weight of the stem and yield parameters namely; number of flowers, pegs and pods as well as the dry mass of pods, kernels and the kernel yield ( kg ha-1.) In the plant spacing/density experiment, vegetative growth among the elite varieties was highest during the March, 2008 rain season whereas yield parameters were higher during the October, 2007 rain season with less rain, this was probably because of excessive vegetative growth during the March, 2008 rain season that contributed to prolonged flowering and delayed podding as assimilates were diverted for vegetative growth. Serenut 1and 2 produced significantly higher vegetative parameters than other varieties during the March, 2008 rain season and the local check variety, Red beauty dominated during the drier October, 2007 rain season. It was also established that plant rectangularity giving rise to higher plant population per unit area (i.e. 10cm between plants) encouraged vegetative growth more than those with lesser plant populations ( i.e. 20cm between plants). Subsequently, whereas Serenut varieties especially Serenut 4 produced more flowers, pegs and pods in March, 2008 rain season, Red beauty produced more in the drier October, 2007 rain season. A correlation analysis of vegetative and reproductive yield parameters carried out for both plant density and intercropping experiments exhibited high correlation of parameters among their categories and moderate or very low correlation across the divide. The reproductive yield parameters were more correlated amongst themselves and so were the vegetative ones. The intercropping experiment exhibited slightly differing results to the plant density experiment. Both the vegetative and reproductive yield parameters were significantly higher in the March, 2008 rain season, with more rain than the October, 2007 rain season. The intercropping treatments did not show significant differences in the majority of the measured parameters except for flowering and podding. Serenuts 1, 2, and 3 produced significantly higher numbers of pods, pod dry matter and kernel yield (kg ha-1 ) in both seasons, especially in the 3-row intercrop treatment, compared to Serenut 4 and Red beauty. The LER analysis carried out indicated that the bunchy Spanish varieties specifically, Serenut 3, Serenut 4 and Red beauty had better intercropping advantage and more so in the 3-row intercrop treatment, basically because of the varieties’ vertical growth habits and the intercrops advantage in reducing inter and intra-specific competition. The GxE analysis carried out showed that on-farm locations yielded significantly higher than on-station, despite less seasonal rain, possibly because of the friable sandy loam soils, as opposed to the massive ferralitic clay loams of Kabanyolo that easily cake and harden when rain declines. Serenut 3 was more adapted to Kabanyolo, while other Serenuts were more suited to other locations. While Kyegonza 1 was the most productive environment in all yield parameters, Serenut 2 yielded significantly more than all the other varieties in all yield parameters. Kabanyolo (MUARIK) and Red beauty were the least productive environment and variety, respectively. Overall, the elite groundnut varieties were found to be superior, more stable and better adapted to different environments. Serenut 3, 2, and 1 produced larger kernels compared to Red beauty and Serenut 4. It is therefore recommended that farmers should adopt these Serenut varieties. Serenut 3 performed better in both the short rains and long rains whereas Serenuts 4, 2, or 1 are better for the long rainfall seasons. The 3-inter row intercropping technique was found to be superior to the 2-inter row intercropping patterns.