Search Result for "nitrogen cycle":
Wordnet 3.0

NOUN (1)

1. the circulation of nitrogen; nitrates from the soil are absorbed by plants which are eaten by animals that die and decay returning the nitrogen back to the soil; 



WordNet (r) 3.0 (2006):

nitrogen cycle
    n 1: the circulation of nitrogen; nitrates from the soil are
         absorbed by plants which are eaten by animals that die and
         decay returning the nitrogen back to the soil