Nitrogen is fixed into the soil not only by biological processes. Elaborate.

Explanation

Nitrogen is fixed into the soil not only by biological processes, it is also done by abiological processes.
(a) In nature due to thunders and lightening dinitrogen is converted into nitrogen oxides.
`N_(2) + O_(2) rarr 2NO` (nitric oxide)
`2NO + O_(2) rarr 2NO_(2)` (nitrogen dioxide)
`2NO_(2) + H_(2)O rarr HNO_(2)//HNO_(3)` (nitrous/nitric acid)
`HNO_(3) + Ca//K` salts `rarr` Ca/K (nitrates)
When nitrous/nitric acid reach the soil reacts with the alkali radical to form nitrates.
(b) Industrial combustions, forest fires, automobile exhausts and power-generating stations are also the source of nitrogen oxides.