Chemistry – Chemistry of the environment - Fertilisers | e-Consult

Nitrogen fixation is the process by which atmospheric nitrogen (N₂), which is unusable by plants, is converted into ammonia (NH₃) or ammonium ions (NH₄⁺) that plants can utilize. This is primarily carried out by certain bacteria, either free-living in the soil or in symbiotic relationships with the roots of legumes (e.g., peas, beans, clover). These bacteria possess the enzyme nitrogenase, which catalyzes the reaction.

The overall chemical equation for nitrogen fixation is:

This reaction requires a significant amount of energy (high temperature and pressure) and is typically carried out in the nodules on legume roots. The ammonia produced is then converted to ammonium ions (NH₄⁺) in the soil.

Nitrogen fixation is crucial for fertilizer production because it provides a natural source of usable nitrogen. Historically, the large-scale industrial production of ammonia (Haber-Bosch process) replaced natural nitrogen fixation as the primary method of obtaining nitrogen for fertilizers. However, understanding nitrogen fixation is important for appreciating the biological basis of nitrogen availability in agricultural systems and for developing sustainable agricultural practices.