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The world rise in millions of metric tons (Tg) of N in fertilizer, and plotted above each year, the annual percentage change in the world and U.S. calculated from 4 yr before until 5 yr later [source: World, http://www.fertilizer.org; for U.S., Agricultural Handbook 712 (USDA, Washington, DC, 1997) and http://mann77.mannlib.cornell.edu/data-sets/inputs/86012].
