Growth and Yield Responses of Vegetable Cowpea (Vigna unguiculata (L.) Walp.) Varieties to Lime Rates in Acid Soil of South Eastern Nigeria
The amendment of acidic soil with lime application enhances nutrient availability for optimum vegetable cowpea production. Field experiments were conducted in the teaching and research farm of Michael Okpara University of Agriculture, Umudike during 2006 and 2007 cropping seasons to determine the growth and yield responses of three vegetable cowpea varieties, IT93K-915 (white seeded and climbing vines), IT86D-880 (brown seeded and erect vines) and Akidi ani (black seeded and spreading vines) to five rates (0, 0.5, 1.0, 1.5 and 2.0 t//ha) of lime (Ca(OH)<sub>2</sub>). The experiment was laid as a 3 x 5 factorial in randomized complete block design (RCBD) and replicated three times. Liming progressively increased the soil pH, most of the growth and yield attributes, such as percentage germination, number of nodules per plant, number of branches per plant, number of leaves per plant, vine length, fresh pod weight, fresh and dry pod yields, grain yields/ha and 100-seed weight. Lime application at 2.0 t/ha and 0 t/ha performed best and poorest in terms of the growth and yield of the vegetable cowpea respectively. The variety, IT860D-880 produced highest fresh pod and grain yields per hectare whereas IT93K-915 and Akidi ani had more number of branches and leaves. The application of 2.0 t/ha lime to IT86D-880 produced heaviest fresh pods, more seeds per pod and highest grain and fresh pod yields in both 2006 and 2007. The combination, therefore, is recommended for farmers in this area as the results suggest that the amendment of the acidic soil with lime application increased the soil pH which could have enhanced nutrient availability for the optimum vegetable cowpea production especially the improved variety, IT86D-880.
Keywords: Vegetable cowpea, lime, variety, fresh pod, grain yield, 100-seed weight.