The nitrogen cycle is said to be a perfect cycle. Explain, why?

CBSE Class 9 CBSE Class 9 Science
1

The nitrogen cycle is said to be a perfect cycle. Explain, why? Name two non-leguminous plants which can fix free nitrogen.

2

Nitrogen cycle is said to be a perfect cycle keeps the overall amount nitrogen content in the atmosphere and hydrosphere constant and nothing is lost.
Two non-leguminous plants which can fix free nitrogen are Parasponia and Alnus.