Effect of Phosphorus fertilizer on growth and yield of cowpea (Vigna unguiculata)

Phosphorus is important for cowpea production in many tropical African soils with inherent low phosphorus fertility. Most farmers in Africa, however, do not have access to phosphorus fertilizer. Selection of cowpea lines that produce good yield under low soil phosphorus or those with high phosphorus use efficiency can be a low input approach to solving this problem. This research work was conducted in pot trials at the teaching and research farm of Michael Okpara University of Agriculture, Umudike, in the south eastern part of Nigeria to determine the effect of different phosphorus levels on growth and yield of three varieties of cowpea (Vigna unguiculata (L.) Walp), obtained from the germplasm unit of International Institute of Tropical Agriculture, Ibadan. The experiment consists of five phosphorus levels (0kgha -1 , 20kgha -1 , 40kgha -1 , 60kgha -1 and 80kgha -1 ) each of which contains seven replicates. Phosphorus fertilizer significantly enhanced growth and yield characters of the cowpea varieties used; plant height, leaf area, number of leaves and number of branches in all the weeks of measurement were significantly improved. Phosphorus also had a significant effect (p> 0.05) on seed yield per treatment, weight of 50 seeds, number of nodules, weight of nodules and total aboveground dry matter in all varieties used. However, variations were observed in the responses of the different cowpea varieties to phosphorus application. High yield values were observed in variety three; IT99K-573-2-1, followed by variety two; IT99K-573-1-1 and variety one; IT97K-499-35. Highest value in all the yield characters measured was observed in variety three: IT99K-573-2-1 at phosphorus fertilizer rate of 40kgha -1 . When phosphorus is available, IT99K-573-2-1and 40kgha -1 phosphorus application rate is recommended.