What is the primary method of nitrogen fixation used in agriculture?

Biological nitrogen fixation through legumes is a primary method of nitrogen fixation utilized in agriculture due to its role in converting atmospheric nitrogen into a form usable by plants. This process occurs through symbiotic relationships between legumes and specific bacteria, such as Rhizobium, which reside in the root nodules of these plants.

When legumes are planted, these bacteria take nitrogen gas from the atmosphere and convert it into ammonia, a form of nitrogen that plants can assimilate. This naturally enriches the soil with nitrogen, reducing the reliance on synthetic fertilizers and improving soil fertility over time. Additionally, rotating legumes with other crops enhances soil health and increases overall agricultural productivity.

Other methods mentioned, such as burning plant residues and mechanical tilling, do not contribute to nitrogen fixation. Burning can lead to the release of nitrogen back into the atmosphere rather than enriching the soil, while mechanical tilling primarily serves to prepare the soil for planting but does not influence nitrogen levels directly. The application of nitrogen-containing fertilizers offers a quick way to supply nitrogen but does not produce new nitrogen; rather, it adds available nitrogen to the soil, which can lead to environmental issues if overused.