1. Conversion of free nitrogen of air into nitrogenous compounds that are made available to plants for uptake is known as : nitrogen fixation.
2. Physical nitrogen fixation occurs in step- : wise manner and it takes place in atmosphere j and soil.
3. Under the influence of electric discharge, lightning and thunder, atmospheric nitrogen combines with oxygen to form nitric oxide.
4. Nitric oxide is then oxidized to nitrogen peroxide in presence of oxygen.
5. Nitrogen peroxide combines with rainwater to form nitrous and nitric acid which come on ground as acid rains.
6. On ground, alkali radicals (mainly of Ca, K) react with nitric acid to produce nitrites and nitrates which are absorbable forms for plants.
