Question
What are biogeochemical cycles? Explain how nitrogen is fixed in the atmosphere.
Solution
The cyclic movements of chemical elements of the biosphere between the living organisms and the environment are referred to as biogeochemical cycles.
Bio refers to living organisms and geo refers to rocks, soil, air and water on the earth.
Nitrogen is a major constituent of the atmosphere comprising of about 78% of the atmospheric gas.
Ninety per cent of fixed nitrogen is biological. The principal source of free nitrogen is the action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil. Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation. In the oceans, some marine animals can fix it. After atmospheric nitrogen has been fixed into an available form, green plants can assimilate it.
