Overall, fertilizer production, legume crops, and fossil fuel burning deposit approximately 140 Tg of new
nitrogen into land-based ecosystems each year, a figure that equals the upper estimates for nitrogen fixed naturally
by organisms in these ecosystems.
Other human activities liberate and make available half again that much nitrogen.
From this evidence, it is fair to conclude that human activities have at least doubled the transfer of nitrogen from the atmosphere into the land-based biological nitrogen cycle.