Enhancement of soybean productivity and nutritional properties by use of exogenous Rhizobium isolates

Soybean is a vital nutritional resource rich in protein, oil, vitamins, and minerals, serving as a leading global source of vegetable oil and helping combat undernourishment, especially in developing countries like Cameroon, where over 24 % of the population faces food insecurity. However, insufficient nutrients can severely hinder the formation of fruiting bodies, resulting in yields as low as one ton per hectare. This study explores the potential of enhancing nitrogen nutrition through Rhizobium bacteria to improve nodulation rates and overall soybean productivity. The objective was to assess the effects of various Rhizobium isolates on the productivity, physicochemical properties, and nutritional quality of soybeans, essential for agricultural development and food security. The experiment was carried out at IRAD Mbalmayo from March–July and September–November 2022. The experimental set-up was a completely randomized block design replicated thrice. Each replicate consisted of three elementary plots separated by 1 m. Crops were planted at 50 cm between rows and 10 cm between plants. Five treatments: control (S0), Rhizobium isolate No.1 (S1), Rhizobium isolate No.2 (S2), NoduMax (S3), NPK: 20-10-10 (S4), were applied to three varieties: V1 (TGX 1910–14F), V2 (MAKSOY 4N), V3 (TGX 1835 10E). Results showed that seed emergence rates varied from 69% to 99% among soybean varieties, with no significant differences across treatments. Notably, Rhizobium inoculation, particularly with isolate 2, significantly boosted growth, leading to greater plant height, leaf count, and flowering duration. The highest plant height recorded was 35.3 cm in the V2S2 treatment, while V1S2 had the highest number of leaves, reaching 43.73, at P = 0.05. Inoculated plants showed substantial yield improvements, achieving 2.9 tons per hectare, with increased pod and seed formation. Analysis of treated plants revealed variations in nitrogen, lipid, protein, carbohydrate, ash, and moisture content, underscoring the positive impact of inoculation. For example, lipid content ranged from 15.7% in V1S0 to 25.1% in V1S2, while the highest protein levels were recorded in V2S2 and V1S2. These results underscore the potential of Rhizobium inoculation as a sustainable strategy to enhance soybean production and contribute to food security.