Indigenous bradyrhizobia populations in tropical farm-lands

Abstract

Using the plant‐infection technique, and soybeans as test plants, counts of root nodule bacteria in seven farm‐lands in Southern Nigeria were estimated. All sites including those without a recent legume cover history contained bradyrhizobia. Abundance, however correlated with the presence of a legume. Populations varied from 0.95 to 3.63 log10 rhizobia per g soil. In addition to the presence of a legume, soil moisture and pH appeared to influence the rhizobial distribution in these soils. Most of the nodules produced on the test plant were ineffective, indicating that the rhizobial presence alone does not guarantee adequate N2 fixation in a farming set‐up.