تثبيت النيتروجين
Nitrogen fixation, the process by which diatomic nitrogen gas is converted to ammonium ions and becomes available to plants, was also investigated by Beijerinck. Bacteria perform nitrogen fixation, dwelling inside root nodules of certain plants (legumes). In addition to having discovered a biochemical reaction vital to soil fertility and agriculture, Beijerinck revealed this archetypical example of symbiosis between plants and bacteria.