Response of cowpea (Vigna unguiculata [L.] Walp) to nitrogen and phosphorus fertilizers and residual fertility effects on growth and yield of maize (Zea mays L.)

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SEPTEMBER, 2015
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Generally, soils in tropical Africa including Ghana are inherently low in essential nutrients particularly nitrogen and phosphorus thereby resulting in low yields of crops. To this end, two field experiments were conducted on the same plot at the Plantation Section of the Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology (KNUST) during the major and minor cropping seasons of 2014 to evaluate cowpea (Vigna unguiculata [L.] Walp) response to nitrogen and phosphorus fertilizers and residual fertility effects on the growth and yield of succeeding maize (Zea mays L.) crop. The design used in the studies was a 4×5 factorial arranged in randomized complete block with three replications. The factors studied were N and P fertilizer application rates. The N rates were 0, 10, 20, 30 and 40 kg N/ha and the P rates were 0, 15, 30 and 45 kg P2O5/ha. The Asontem cowpea and Abontem maize variety used were obtained from the CSIR- Crops Research Institute, with both having a maturity periods of 65 and 75 days respectively. The land was ploughed, harrowed and plots were laid out. Plot size was 4.1 × 1.9 m. Planting for the cowpea was done in June at a spacing of 60 × 20 cm, while that of the maize was done in September at a spacing of 70 × 30 cm. All necessary agronomic practices were carried out. The results indicated that cowpea growth indices were not significantly (P > 0.05) affected by N and P fertilizer application rates. All nodulation parameters were also not significantly (P > 0.05) affected by N and P rates, except for number of nodules at 4 weeks after fertilizer application (WAFA). Grain yield and its component were not significantly (P > 0.05) affected by N and P fertilizer application rates. The results further indicated that residue quality was not responsive (P > 0.05) to N and P rates. However, application of N had significant (P < 0.05) effects on cowpea total plant N, seed N and crude protein content of seeds. Furthermore, residual fertilization did not significantly (P > 0.05) affect the growth, dry matter and grain yield of the succeeding maize crop. From the studies, it is recommended that, application of N to cowpea fields should highly depend on the N status of that particular field and that further studies should be conducted with higher P rates in other to determine the appropriate rate of P fertilizer that will produce significant effects on growth, grain yields and N contents of whole plant, seeds and residues of cowpea.
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A thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture of the College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in partial fulfillment of the requirement for the award of Master of Philosophy Degree in Agronomy (Crop Physiology),
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