Describe the two known major natural mechanisms for converting atmospheric nitrogen to useable forms.

(a). Biological fixation

(b). Fixation by lightning

Explanation:

Gaseous nitrogen in the atmosphere has to be converted or "fixed" into a suitable form before it can be utilised by living organisms.

There two main ways of nitrogen fixation are

(a). Biological fixation: Majority (approximately 90%) of nitrogen fixation is carried out by bacteria. Bacterias such as Cyanobacteria transforms nitrogen into ammonium and ammonia : N2 + 3 H2 → 2 NH3. The produced ammonia can then be taken in directly by plants and / or the conversion products of ammonium and ammonia may further react in the process of nitrification.

(b). Fixation by lightning: Lightning energy causes the combination nitrogen (N2) and water (H2O) forming nitrates (NO3) and ammonia (NH3). Rain water dissolves the formed nitrates and ammonia and the solution is drained into the ground, where they can be reached by plants plant roots for consumption.