Effects of Bradyrhizobium japonicum and Phosphorus Supplementation on the Productivity of Legumes

Most soils in sub-Saharan Africa are depleted and lack important nutrients for proper plant growth and development. The declining trend of soil fertility pronounced in different parts of Africa is attributed to different factors such as continuous cropping without soil replenishment and land degradation leading to poor grain yield of legumes. Nitrogen and phosphorus are among the most limiting nutrients for plant growth as they play different roles in the biochemical processes of plants. Phosphorus is a fundamental component of substances that are building blocks of genes and chromosomes. Adequate supply of phosphorus is essential for development of new cells and the transfer of the genetic code from one cell to another during cell formation. Nitrogen is an essential constituent of plant cells at structural, genetic and metabolic levels, involved in many processes of plant growth and development leading to yield and quality of harvested organs. Traditionally, small-scale farmers use little or no farm-yard manure and chemical fertilizers to improve soil nutrition. However, these fertilizers are expensive to be afforded by small-scale farmers. The alternative to this is the use of cheap and easily applied biofertilizer such as Rhizobium bacteria that can fix atmospheric nitrogen to the form that can be taken by plants. The potential role of rhizobia inoculants and P application with respect to growth, nitrogen fixation, nutrient uptake, total leaf chlorophyll content, and grain yield of legumes are given attention in this review. The results from different researchers showed that Rhizobium inoculation and supplementation of phosphorus independently or in combination had positive effects on growth, leaf chlorophyll content, nutrients uptake, grain yield, and nitrogen fixation. Therefore, reducing N and P deficiencies in the soil through the use of biofertilizers such as Rhizobium inoculants and phosphorus supplementation is a good option in promoting legume yield.