"10.1146/annurev.environ.032108.105046" . "Nitrogen in Agriculture: Balancing the Cost of an Essential Resource"^^ . . "34" . "97-125" . "2009"^^ . "10.1146/annurev.environ.032108.105046" . . . _:genid1 . _:genid1 . _:genid1 . _:genid1 . _:genid1 . _:genid2 . _:genid2 . _:genid2 . _:genid2 . _:genid2 . . . . . . .