Effectiveness of native Rhizobia isolates on productivity of climbing beans on limed acidic soil of Rwanda.

Abstract

Farmers in sub Saharan Africa are financially constrained to afford mineral fertilisers despite the Abuja declaration of 2006 to apply at least 50 kg ha-1 of plant nutrients in soil. Whereas P and K can mainly be sourced from the expensive mineral fertilizer, adequate N may be cheaply derived from the atmosphere through biological nitrogen fixation. Yet, climbing bean production in Rwanda is constrained by soil nitrogen and acidity. Thus, the goal of this study was to increase the production of climbing beans using low cost inputs soil management practices. The objectives of the study were to (i) determine the richness of native rhizobia in the acidic soils under different management practices for enhanced BNF; (ii) determine effectiveness of the native rhizobia strains in acidic soils under different management practices on the climbing beans in Rwanda; (iii) determine the effect of liming on biological nitrogen fixation in inoculated climbing beans. A preliminary study was done to isolate native rhizobia strains following standard methodology. The isolated effective native strains SMP104 and SMP63 were compared against a Mak bio fixer (from Makerere University) and ISAR strain (Rwanda Agriculture Board). Lime CaCO3 was applied at 0, 2.5 and 4 t ha-1 arranged in a completely randomized design in the greenhouse. Dry matter and plant N uptake increased significantly following inoculation and lime application. The isolated native strains SMP104 and SMP63 were superior on both climbing bean varieties in increasing total dry matter, nodulation and effectiveness compared to the Mak bio fixer and ISAR strains. Liming at 2.5t ha-1 was not significantly different from 4 t h-1 on BNF indicator parameters. Therefore, those native isolates and liming at 2.5t ha-1 of lime can be recommended for use in low-nitrogen environment as well as procreation materials.