nitrogen balance

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The difference between the amount of nitrogen ingested by an animal or taken in by the soil and the amount excreted or lost.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the balance between the amount of nitrogen taken in (to the soil or the body) and the amount given off (lost or excreted)