Influence of groundnut varieties and bradyrhizobium-phosphorus combination on soil nitrogen content in Maiduguri, Nigeria

Abstract

A field experiment was conducted at the University of Maiduguri Teaching and Research Farm to evaluate the effects of Bradyrhizobium inoculation and phosphorus application on soil nitrogen content. Treatments comprised a factorial combination of three groundnut varieties (SAMNUT24, Bomboy and Exdakar) and six inoculant-phosphorus combinations (Br₀ + P₀, Br₀ + P₄₀, Br₀ + P₆₀, Br₁ + P₀, Br₁ + P₄₀ and Br₁ + P₆₀), where Br₀ and Br₁ represent uninoculated and inoculated plants, respectively, while P₀, P₄₀ and P₆₀ denote phosphorus application rates of 0, 40 and 60 kg P₂O₅ ha⁻¹, arranged in a Randomized Complete Block Design with three replications. Nitrogen concentration and content in groundnut, biological nitrogen fixation, and soil nitrogen content before and after the experiment were assessed. Data were analysed using analysis of variance at the 5% significance level. Bradyrhizobium-phosphorus combinations significantly influenced nitrogen derived from the atmosphere (Ndfa) and soil nitrogen content. Varietal effects on nitrogen fixation were significant, with Bomboy recording the highest nitrogen fixed (47.428 kg N ha⁻¹) and Ndfa (82.746%). SAMNUT24 contributed 1.135 g kg⁻¹ soil nitrogen, representing a 63.06% increase over the initial value. Variety × inoculant-phosphorus interactions significantly affected root nitrogen content (p = 0.034), Ndfa (p = 0.023) and soil nitrogen content (p = 0.001). Bomboy + Br₁ + P₄₀ maximised nitrogen fixation, whereas SAMNUT24 + Br₁ + P₀ produced the highest post-harvest soil nitrogen content (1.77 g kg⁻¹). These combinations are recommended for improving nitrogen fixation and soil nitrogen status, respectively, under similar conditions.