Evaluation of the effect of bradyrhizobium CB 756 inoculation on biological nitrogen fixation efficiency in cowpea accessions

Abstract

Cowpea is a highly important crop in economic, nutritional and environmental terms. Economically, it’s a source of livelihood to millions of relatively poor households in the less developed countries of the tropics through them participating in the trade of cowpea grain and its associated products. It’s a multipurpose crop, the grains, leaves and pods are eaten as food and its shoot biomass acts as nutritious feed to livestock. Cowpea is highly rich in protein, vitamins and other mineral elements making it important for both animal and human health. Cowpea is a good atmospheric nitrogen fixer hence does not stress the nitrogen reserves of the soil. This makes it a viable intercrop option, it’s a good green manure source and provides a thick cover over the soil. The crop is hardy and tolerant to droughts and poor soil fertility, conditions that are prevalent in the tropics. Despite these good attributes of cowpea, its production in Uganda remains low as per international standards. The low yields are attributed to various factors to which low soil fertility and lack of efficient rhizobia strains in a majority of the soils of the tropics are major factors. In a quest to improve the yields synthetic nitrogen fertilizers can be used however this approach is unsustainable in economic and environmental fronts. Livestock manure application can also be an option but its nutrient content is low and large amounts are required to meet the plant nitrogen requirement. However the enhancement of biological nitrogen fixation through inoculation with effective bio fertilizers is an approach that can improve the yields of cowpea in a sustainable way. Inoculation of cowpea with bio fertilizer has been seen to increase growth and yield. With all this said specific information on the response of cowpea to inoculation with Bradyrhizobium CB 756 strain in Uganda agro ecology is not sufficient. This research was therefore conceived with the aim of finding out how various cowpea genotypes respond to Bradyrhizobia CB 756 inoculation in regards to their biological nitrogen fixation. Information on such responses can be of use in cowpea genotype characterization and in proper inoculum application. In this regard an experiment was set up under a screen house at MUARIK.