Physical Nitrogen Fixation

Physical Nitrogen Fixation:- The process of converting nitrogen gas into a useful form for plants and other organisms in a biological process is called physical nitrogen fixation. Ammonia is produced industrially by direct mixing of nitrogen with hydrogen at high temperatures and pressures. Later, it is converted into various types of fertilizers like urea, etc.

i. Natural Nitrogen Fixation:- Under the influence of lightning (i.e., electric discharge in the clouds) and thunder, N2 and O2 of the air react to form nitric oxide (NO). The nitric oxides are again oxidized with oxygen to form nitrogen peroxide (NO2).

> The reactions are as follows:

N2 + O2 Lightning → Thunder 2N0 (Nitric Oxide); 2NO + O2 → 2NO2 Oxidation (Nitrogen peroxide)

> During the rains, NO2 combines with rain water to form nitrous acid (HNO2) and nitric acid (HNO3). The acids fall on the soil along with rain water and react with the alkaline radicals to form water soluble nitrates (NO3-) and nitrites (N02-).

2NO2 + H2O → HNO2 + HNO3; HNO3 + Ca or K salts → Ca or K nitrates

> The nitrates are soluble in water and are directly absorbed by the roots of the plants.

ii. Industrial Nitrogen Fixation:- Ammonia is produced industrially by direct combination of nitrogen with hydrogen (obtained from water) at high temperature and pressure. Later, it is converted into various kinds of fertilizers, such as urea etc.