What is the name of the nitrogen-fixing bacteria commonly found in soil?

The term "nitrogen-fixing bacteria" refers to microorganisms that can convert atmospheric nitrogen (N2) into ammonia (NH3), which can then be utilized by plants. One of the most recognized nitrogen-fixing bacteria that specifically forms a symbiotic relationship with leguminous plants is Bradyrhizobium japonicum. This bacterium is particularly important for soybean crops, as it colonizes the root nodules of these plants, facilitating effective nitrogen fixation which enhances soil fertility and contributes to sustainable agricultural practices.

In contrast, while Rhizobium meliloti is also a nitrogen-fixing bacterium, it is primarily associated with alfalfa rather than soybeans. Azospirillum brasilense is known for its ability to associate with non-leguminous plants and contributes to nitrogen fixation, but it does not form root nodules in the same way as the other two. Nitrosomonas eutropha, on the other hand, plays a role in the nitrification process rather than nitrogen fixation. This highlights the specificity of Bradyrhizobium japonicum to soybean crops, making it the most relevant answer to the question regarding nitrogen-fixing bacteria commonly found in soil.