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Physiological Responses of Cowpea Varieties in Minna, Nigeria: Impact of Rhizobia Inoculation, Phosphorus Application, and Sequential Cropping System.
ABSTRACT
Cowpea, the most significant grain legume in Nigeria, faces challenges with low yields on farmers’ fields compared to its potential. This study aimed to enhance cowpea productivity and profitability per unit area in Minna, Nigeria, through various interventions. A glasshouse and two field experiments were conducted between 2015 and 2017.
The glasshouse experiment explored the impact of nitrogen sources (uninoculated, inoculated with USDA 3451 and USDA 3384 rhizobia strains, and 90 kg N ha-1) and two cowpea varieties (IT93K-452-1 and IT99K-573-1-1) using soils from 20 locations in the Nigerian savannas. The first field experiment, conducted on farmers’ fields in Minna, involved three nitrogen sources, three phosphorus rates, and three varieties (IT93K-452-1, IT99K-573-1-1, and TVX-3236) in the first year, with different strains and nitrogen applied in the second and third years.
The second field experiment evaluated the performance of six cowpea varieties (IT93K-452-1, IT99K-573-1-1, TVX-3236, Kanannado, Oloyin, and IT90K-76) in a sequential cropping system. The study assessed growth, yield, nodulation, and physiological parameters. Rhizobia inoculation significantly increased nodulation in 11 locations, with a percentage increase of 4 to 43%. Applying 90 kg N ha-1 resulted in significantly higher biomass yield compared to inoculated and uninoculated plants. Phosphorus application (20 kg P ha-1) increased grain yield by 49-95% over the control.
Certain growth and yield attributes showed significant interactions between rhizobia inoculation, phosphorus, and varieties. IT99K-573-1-1 demonstrated the highest productivity among varieties, while TVX-3236 appeared more phosphorus-efficient with higher growth rate, nodule weight, and grain yield at lower P rates. The number of pods per plant showed the highest correlation coefficient with grain yield.
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, indicating their significance in predicting grain yield. The study confirmed that double cropping of improved, early, and medium maturing cowpea varieties per season (IT93K-452-1, IT99K-573-1-1, TVX-3236, and IT90K-76) increased productivity and profitability compared to traditional planting methods.
Overall, these results suggest that nitrogen limitation can be overcome through rhizobia inoculation with highly effective strains. Furthermore, utilizing CGR, LAI, and Phi 2 can help increase cowpea grain yield through agronomic practices and breeding programs. Application of 20 kg P ha-1 is sufficient for optimal cowpea performance in the study area, and double cropping of improved varieties can enhance cowpea productivity and profitability.
Physiological Responses of Cowpea Varieties in Minna, Nigeria: Impact of Rhizobia Inoculation, Phosphorus Application, and Sequential Cropping System.
