Question

What is a nitrogen cycle?explain in 100 words

Answer 1

Nitrogen forms nearly 78% or the largest part of the earth's atmosphere. But, atmospheric nitrogen is available only in a limited way for biological use. This, therefore, leads to a scarcity of usable nitrogen in many ecosystems.
Nitrogen cycle is the biogeochemical process by which nitrogen is converted into different chemical forms as it circulates in the atmosphere and in the terrestrial and marine ecosystems. The various processes in the nitrogen cycle can broadly be classified as fixation, ammonification, nitrification and denitrification. Ecologists are particularly interested in the nitrogen cycle as nitrogen's availability could affect the rate of the key ecological processes such as primary production and decomposition. 

Answer 2

through which nitrogen is converted into many forms, consecutively passing from the atmosphere to the soil to organism and back into the atmosphere. It involves several processes such as nitrogen fixation, nitrification, denitrification, decay and putrefaction.