Nitrogen is commonly the most limiting plant nutrient in arable farming in the tropics and the most expensive mineral fertilizer element. Biological N fixation, as a biological process of capturing atmospheric N, holds a great promise to small-holder farmers particularly in the Northern Guinea Savanna (NGS) of Nigeria, where the soil is characterized low fertile. There is also a high cost of chemical fertilizers and environmental impacts. Differences among legumes, for ability to grow on low or high P soil exist, the mechanisms involved are not fully understood and few are vaguely described....