Approximately 80% of earth’s atmosphere is nitrogen gas (N2). Unfortunately, N2 is unusable by most living organisms. Plants, animals and microorganisms can die of nitrogen deficiency. All organisms use the ammonia (NH3) form of nitrogen to manufacture amino acid, proteins, nucleic acids and other nitrogen-containing components necessary for life. Maximum biological nitrogen fixation takes place in leguminous crop. In legumes and a few other plants, the bacteria live in small growth on the roots called nodules. Within these nodules, nitrogen fixation is done by the bacteria, and the NH3 they produce is absorbed by the plants. Nitrogen fixation by legumes is a partnership between a bacterium and a plant. The root nodule associations were the first to be recognized for their ability to fix atmosphere N2. Rhizobia are the first group of organism realized for its potential of nitrogen fixation.