Figure 1.5. Global Trends in the Creation of Reactive Nitrogen on Earth by Human Activity, with Projection to 2050

(teragrams nitrogen per year)

"Most of the reactive nitrogen produced by humans comes from manufacturing nitrogen for synthetic fertilizer and industrial use. Reactive nitrogen is also created as a by-product of fossil fuel combustion and by some (nitrogen-fixing) crops and trees in agroecosystems. The range of the natural rate of bacterial nitrogen fixation in natural terrestrial ecosystems (excluding fixation in agroecosystems) is shown for comparison. Human activity now produces approximately as much reactive nitrogen as natural processes do on the continents (R9 Fig 9.1).
(Note: the 2050 projection is included in the original study and is not based on MA scenarios). "

Source: Millennium Ecosystem Assessment
 Synthesis Report (2005),
Chapter 1, p.35