Role of Rhizobia Bacteria and Nitrogen Fertilizer Levels in Enhancing Nutrient Uptake, Growth, and Yield of Cowpea (Vigna unguiculata) Under Saline Irrigation Conditions

Abstract

A pot experiment was conducted during the spring season on February 18, 2026, to evaluate the effect of Rhizobia strains isolated from root nodules of cowpea plants grown in a saline environment, combined with varying levels of nitrogen fertilizer, on enhancing cowpea growth, yield, and nutrient uptake under irrigation with water of differing salinity levels. The experiment comprised three irrigation salinity levels (2, 4,8) dsm^-1, three inoculation treatments with molecularly identified Rhizobia strains uninoculated control (R0), inoculation with Brady rhizobium japonicum (Rj), and inoculation with Brady rhizobium sp. (Rbr) and three nitrogen fertilizer levels (40%, 60%,80% of the recommended rate of 60 kg H ^1- applied as urea, (46% N). The results revealed that inoculation with Rj and Rbr combined with the 80% nitrogen fertilization level under 8 dsm-1 saline irrigation significantly increased total leaf chlorophyll content, leaf nitrogen, phosphorus, and potassium concentrations, total yield, and seed protein percentage compared to the uninoculated control (R0). These findings demonstrate that bio inoculation can reduce production costs by decreasing recommended mineral nitrogen inputs, mitigate environmental pollution associated with excessive synthetic fertilizer application, maintain soil fertility, and support sustainable agricultural practices in freshwater-scarce regions.