Response of local and improved cowpea varieties to Rhizobia inoculation and phosphorus in West Nile region of Uganda

Cowpea (Vigna unguiculata L.Walp) is an important food security and cash crop among poor households especially in eastern and northern Uganda. However farmers have reported grain yields as low as 50 kg ha-1, far below the potential yield of cowpea estimated at 2500 kg ha-1. This study compared responses of two cowpea varieties: Agondire, a local spreading landrace, and SECOW 2W, an improved variety to inoculation with Rhizobia and phosphorus fertilization for adaptation to Northern Uganda’s West Nile sub-region. We tested the hypothesis that the local landrace cowpea variety could perform as good as or even better than the improved cowpea variety when subjected to similar conditions. To test this hypothesis, the two cowpea varieties were subjected to four levels of phosphorus: P0, P10, P20 and P40 kg ha-1 without (-R) or with (+R) inoculation with Rhizobia in a randomized complete design replicated thrice with slope as the blocking factor during the short and long rains of 2015. Data were collected on nodule effectiveness and grain yield and subjected to ANOVA using the GenStat statistical package. Initial soils characterization showed low soil fertility with low organic matter, nitrogen, phosphorus and potassium far below the critical levels for optimization of crop yields in tropical soils. Agondire responded significantly (p < 0.05) better than SECOW 2W when high rates of inorganic phosphorus were applied with Rhizobia inoculation. At the low rates of P with Rhizobia inoculation, SECOW 2W performed better at P (20 and 10 kg ha-1). The study therefore recommends SECOW 2W, which responds better to Rhizobia inoculation at low rates of P fertilizer.