Responses of cowpea (Vigna unguiculata L. Walp) varieties to rhizobia inoculation, phosphorus application and sequential cropping system in Minna, Nigeria

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My study aimed to exploit rhizobia inoculation, phosphorus application, varietal differences and sequential cropping system to improve the productivity and profitability of cowpea per unit area in Minna, Nigeria. Glasshouse and field experiments were conducted between 2015 and 2017. The treatments evaluated during the study were: five rhizobial strains (USDA 3451, USDA 3384, BR 3262, BR 3267, control), three phosphorus rates (0, 20 and 40 kg P ha-1), six varieties of cowpea and soils were collected from 20 locations in Nigerian savannas. Data were collected on growth, nodulation, yield and physiological parameters.

Summarily, results revealed that the cowpea varieties successfully formed symbiosis with the introduced rhizobia strains in all the locations. Rhizobia inoculation increased nodulation in 11 out of the 20 locations with percentage increase ranging from 4 to 43%. Plants fertilized with 90 kg N ha-1 had significantly (P≤0.05) higher biomass yield than the inoculated and uninoculated plants which had similar biomass yield; suggesting the need to test more effective cowpea inoculants in Nigerian savannas. Rhizobia inoculation significantly (P≤0.05) increased the seed protein content of the cowpea varieties. Phosphorus significantly (P≤0.05) increased the photosynthetic activities, nodulation, N-fixation, growth and yield of the cowpea varieties in the three years with application of 20 kg P ha-1 increasing grain yield by 49-95% over the control. Crop growth rate (CGR), leaf area index (LAI) and quantum yield of photosystem II (Phi 2) explained 67.29% of the variation in grain yield (R2= 67.29%). The six varieties tested were successfully planted in two sequence in each growing season except Kanannado. IT93K-452-1, IT99K-573-1-1, TVX-3236 and IT90K-76 varieties had significantly higher (P≤0.05) grain yield and higher profitability than Oloyin and Kanannado varieties which were produced at a loss in the first planting. Planting these four varieties in sequential cropping system increased the profitability by 157-236% than the traditional practice of planting once in a season.

My thesis write-up is completed and I have presented my internal exit defense. I am awaiting the external defense which will come up shortly. The results of the experiments were presented in World Cowpea Conference 2016, International Association of Research Scholars and Fellows symposium 2017 and 2018, International Conference of Agriculture and Agricultural Technology, 2018, Association of Seed Scientists’ of Nigeria Annual Conference, 2019. Some of the results were also published in Production Agriculture and Technology Journal, 2018; 14(2): 131-139. I am awaiting publications from other journals.

Adediran Olaotan Abimbola, Federal University of Technology, Minna, Nigeria (Click here for her 2018 update)