Inputs of nitrogen to terrestrial and aquatic ecosystems have increased several-fold over the last one hundred and fifty years, with the steepest increases during the last four decades. The expansion of fertilizer manu facture and use, the increase in fossil fuel combustion, the intensification of animal husbandry, and widespread cultivation of N2 fixing crops have all contributed to the dramatic increase in N inputs. The increase has been most rapid in Northern Hemisphere (NH) temperate ecosystems, but presently subtropical and tropical regions of Asia are also experiencing an explosive...