Growth and yield of cowpea (Vigna unguiculata) following nitrogen fertilizer application and inoculation

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November, 2016
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A field study was conducted to assess the growth and yield of cowpea (Vigna unguiculata) following N fertilizer application and inoculation at the Plantation Section, Faculty of Agriculture, KNUST. Two inoculants (Eco-Rhiz-Soya and BR 3262) and nitrogen fertilizer at four levels which (0 kg N/ha, 15 kg N/ha, 30 kg N/ha and 45 kg N/ha) were the two main factors. The initial soil analysis was conducted at the Soil Science Laboratory at KNUST to determine microbial population, pH, phosphorus content, exchangeable cations, organic carbon and organic matter. Planting was done manually at three seeds per hill and later thinned to two seedlings per hill at a spacing of 60 x 20 cm. The N fertilizer was applied two weeks after planting the seeds. Growth parameters measured were number of days to emergence, plant height, number of leaves, leaf area, leaf area index, number of days to 50 % flowering, number of branches, percent effective nodules, number of nodules and nodule dry weight. The yield parameters measured were number of pods, number of seeds per pod, weight of seeds per pod, 100 seed weight, grain yield, residue N and seed N content. The results showed that at 25 and 35 DAP, plants that received 45 kg N/ha were the tallest, and this was significantly higher than all other treatment means and both inoculants produced similar effects, and either effect was significantly higher than the control treatment. The 45 kg N/ha produced the greatest number of branches, and this was significantly higher than the other treatments where as 30 kg N /ha treatment recorded the greatest nodule number plant per plant (2.98) which was significantly higher than all other treatment effects. The 30 kg N /ha treatment produced the greatest number of effective nodules on both sampling periods but the Eco Rhiz soya inoculation produced significantly higher effective nodules than all other treatments at 25 DAP only. The grain yield did differ significantly among the nitrogen fertilizer levels. The 45 kg N/ha treatment recorded the greatest grain yield which was significantly higher than all other treatment effects. Grain yield following inoculation was greatest in the BR 3262 inoculant, which was significantly higher than those of the control and Eco Rhiz soya. The N fixed and N derived from the atmosphere, from the 45 kg N/ha treatment were significantly higher than all other treatments. Inoculation significantly affects mean of N fixed, as the treatment effect of the BR 3262 inoculant was greater than those of the control and the Eco Rhiz soya but N derived from the atmosphere was not significantly different among the inoculation treatments. The results indicated that for greater growth, N fixation and grain yield of cowpea, inoculation or starter N application cannot be overlooked.
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A thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfillment of the requirements for the degree of Master of Philosophy in Agronomy (Crop Physiology),
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