Performance of Soybean Inoculated With Promiscuous Rhizobia Strains Under Acid Soil Conditions of Southern and Eastern Provinces of Rwanda

Abstract

Soil acidity impedes soybean growth by limiting nutrient availability and rhizobia efficiency. The study aimed to identify acid-tolerant rhizobium strains and evaluate their effect on soybean production under low pH conditions, as well as assess the efficiency of native rhizobia isolates in nodulating legumes. It found significant differences in rhizobia isolates from Glycine max, Phaseolus vulgaris, Pisum sativum, and Vigna unguiculata compared to Arachis hypogaea under acidic conditions. Soil parameters, including pH, were highly correlated with nutrient availability, affecting nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and organic carbon levels. Organic carbon was closely related to N content. Significant interactions were observed between soybean variety and soil amendments, with organic manure increasing nodulation in two varieties. Non-inoculated soybean controls had lower N fixation than inoculated treatments, with the BB88E strain showing superior nitrogen fixation. High biomass production led to increased grain yields, attributed to N-fixation by acid-tolerant rhizobia strains, soybean variety, and nutrient applications. Soil acidity limited nutrient mobility and increased aluminum concentration, but elite rhizobia strains significantly improved nitrogen production and soybean yield, offering solutions for soil acidity and nutrient availability. .Legume plants were randomly uprooted at the flowering stage based on farmer typology, and nodules were collected from various crops in Rwanda. The nodulation ability of rhizobia strains was assessed using the Most Probable Number (MPN) method. Three strains were tested under varying acidic conditions in both laboratory and field condition to determine their effectiveness. The study design included a factorial design for the first two objectives and a split-plot design for the rhizobia strains field-testing. The study used the Principal Component Analysis (PCA) and general analysis of variance to assess the impact of soil properties and pH on rhizobia isolates. Acid-tolerant rhizobia and soil amendments enhance soybean growth, nodulation, and nutrient uptake in acidic and neutral soils.