The field and screen house experiment was conducted at Tanzania Coffee Research Institute and Seliani Agricultural Research Institute respectively in Tanzania, between March-July 2013, to assess the effects of Bradyrhizobium japonicum and phosphorus on growth and total leaf chlorophyll content of cowpea. The experiment was out down in splitplot design whereby the main plots comprised two inoculation treatments (with and without B. japonicum), while the sub-plots contained phosphorus (TSP) application at four different levels (0 kg/ha, 20 kg/ha, 40 kg/ha, 80 kg/ha). Both experiments were replicated four times. We measured plant growth parameters such as plant height; number of leaves per plant at different stages of plant growth, the stem girth was measured by vernier caliper at physiological maturity. The chlorophyll content was determined at 3, 5, and 7 weeks after planting (WAP). The chlorophyll was extracted by using dimethylsulphoxide (DMSO) and absorbance was determined at 645 and 663nm using UV/Visible spectrophotometer. B. japonicum inoculation significantly increased the plant height, number of leaves per plants, and stem girth above the control. The height was increased by 11.23, 10.43 and 8.99% (screen-house) and by 8.11, 24.05, 9.29% (field) in the measurements taken at 4, 6, and 8 WAP respectively. Number of leaves per plant counted at 6 and 8 WAP increased by 14 and 10.8% (screen-house) and 14 and 11.6% (field) respectively. B. japonicum also

The current study was conducted to assess the effects of phosphorus supplementation and Bradyrhizobium japonicum inoculation on the availability and uptake of N, P, K, Mg, Ca and Na on cowpea. The experiment was laid out in a split plot design where the main plots comprised two inoculation levels (with and without inoculation of B. japonicum) and sub plots contained four different levels of phosphorus (0, 20, 40, and 80 kg P/ha). The results indicated that B. japonicum inoculation and phosphorus supplementation significantly improved the uptake of N, P, K, Mg, Ca and Na in different cowpea tissues such as roots, pods, shoots, and whole plant relative to the control. The results also indicated that there was a significant interaction of B. japonicum and phosphorus on the uptake of sodium in the roots and whole cowpea plant in the screen house. Rhizobia inoculation and supplementation of phosphorus at 40 kg P/ha resulted in the improved uptake of the most elements over other treatments tested.

The field and screen house experiments were carried out in the 2013 cropping season to assess the effects of B. japonicum inoculation and phosphorus supplementation on the uptake of micronutrients in the cowpea. The experiment was laid out in a split plot design where the main plots comprised two inoculation treatments (with and without B. japonicum inoculation) and sub plots included four different levels of phosphorus (0, 20, 40, and 80 kg P/ha). The results showed a significant improvement in the uptake of micronutrients in the B. japonicum inoculated treatments over the control. Phosphorus supplementation (40 kg P/ha) also showed a significant increase in the uptake of some micronutrients while decreasing the uptake of Zn in some plant organs. There was also a significant interaction between B. japonicum inoculation and phosphorus in the root uptake of Zn for the field experiment.

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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