Influence of Sokoto Phosphate Rock on Some Soil Properties and the Growth and Yield of Cowpea [Vigna Unguiculata (L)Walp.] Varieties in Sudan Savanna of Nigeria

Phosphate rock has been used over the years as source of P fertilizer especial in acid soils. Sokoto state is rich in PR deposit and could be used to complement the conventional P fertilizer whose use by peasant farmers have been limited by high cost and scarcity. Sequel to this, an Experiment was conducted in 2009 at the Botanical Garden, Department of Biological Sciences, Usmanu Danfodiyo University, Sokoto to determine the influence of Sokoto Phosphate Rock (SPR) on some chemical properties of soil, growth and yield of cowpea [Vigna Unguiculata (L)Walp.]. The treatments consisted of factorial combinations of two varieties (Dan Gusau (v1) and IT90K-82-2 (v2) and three levels of SPR at 0.062, 0.125 and 0.187g/5kg (25, 50, 75 kg ha-1) as well as a control (without fertilizer). The experiment was laid out in a completely randomized design (CRD) replicated three times. SPR applied enhanced availability of nutrients in soil and the general performance of cowpea varieties which increased with increased rate of application. The results of the study indicated a significant difference (p<0.05) in soil available phosphorus, plant tissue phosphorus, soil total nitrogen and plant tissue nitrogen due to application of SPR. Significant difference was also observed in plant height at 2, 4, 6, and 8 weeks after planting (WAP). Similarly, the response of cowpea varieties, dry matter yield at harvest (8WAP) due to application of SPR was significant (p<0.05). Significant interaction effect between variety and applied SPR on plant height, number of branches and dry matter yield were also observed. The results of this investigation revealed that, increased rate of application of SPR progressively increased the growth and yield performance of cowpea and soil available phosphorus. However, absolute values were not high perhaps because of the weekly acidic nature of the soil which does not encourage fast solubilization of P from SPR. Therefore, application of SPR at a rate of 75kg ha-1 could improve cowpea production and therefore recommended. Keywords: Sokoto phosphate rock; Soil parameters; Sudan savanna; Cowpea yiel