ABSTRACT
The continued decline in soil fertility, high fertilizer costs and the need to implement environmental friendly agricultural systems are some of the world’s major strategic concerns. Soil microorganisms are part of the soil ecosystem and are reported to contribute in soil fertility improvement. This paper is aimed at highlighting their contributions in alleviating soil fertility decline. The Rhizobium/legume symbiosis, a well known association contributes substantial amounts of biologically fixed nitrogen to cropping systems and significant benefits on yields of crops that follow in rotation. Soil microorganisms such as bacteria and fungi contribute to plant phosphorus nutrition through solubilization of sparingly soluble Al, Fe and Ca phosphates, and mineralization of phosphorus from organic substances. Solubilization is mainly achieved through production of organic acids, chelation and ligand exchange, and other pH lowering mechanisms whereas mineralization is achieved through production of enzymes such as phytases and phosphatases. Mycorrhizal associations are reported to contribute to plant phosphorus nutrition through increasing root surface area for soil exploration, production of phosphorus solubilizing enzymes and acids. Mycorrhizal fungi and bacteria also solubilize other nutrients such zinc, copper, potassium and calcium from their precipitated or sparingly soluble forms. Microorganisms also contribute to soil fertility improvement through their roles in composting. They are currently isolated, studied and packaged as biofertilizers and used to supplement chemical fertilizers. It can be noted that thorough exploitation of microbial activities can contribute to balanced plant nutrition. However, poor soil management practices limit realization of potential benefits from soil microorganisms whereas biofertilizer technology development in developing countries such as Sub-Saharan African countries is derailed because of lack of awareness, infrastructure and human capacity. From this study it can be noted that intensifying soil management practices that maximize microbial activities can go a long way in improving soil fertility with minimal use of chemical fertilizers. On the other hand there is a need to improve both human and infrastructure capacity in poor countries such as those in Sub-Saharan Africa so as to manage research in biofertilizer technologies. Awareness and dissemination of information on the importance of biofertilizers, intensifying effective microbial inoculation where it deemed to give good response and systematic evaluation of economic viability of biofertilizer technologies are other areas that need to be addressed.