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I'm in an AP Environmental Science course, and while reading part of the chapter in my textbook about the nitrogen cycle, I saw this picture.

nitrogen human input

What I was wondering is what caused that dip in the nitrogen input in about 1995? I've researched online, but I haven't found anything.

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    $\begingroup$ I assume it is the fall of the USSR. $\endgroup$ – arkaia Sep 19 '14 at 17:30
  • $\begingroup$ The original figure is based on work by Galloway et al., 2004 (jstor.org/stable/4151466) and Smil, 2004 (Enriching the earth: Fritz Haber, Carl Bosch, and the transformation of world food production. MIT press). I don't have the book now, but he talks about the time evolution of reactive Nitrogen. You could check there. Also useful is: whrc.org/resources/publications/pdf/UNEPetal.2007.pdf $\endgroup$ – arkaia Sep 19 '14 at 18:20
  • $\begingroup$ What exactly is the graph showing? Atmospheric nitrogen fixed in other compounds? $\endgroup$ – mart Sep 23 '14 at 9:04
  • $\begingroup$ @aretxabaleta care to post as an answer? $\endgroup$ – David LeBauer Oct 5 '14 at 3:34
  • $\begingroup$ I'm still trying to get the Smil book back to check on things, but the answer by @DavePhD seems to be the main point. $\endgroup$ – arkaia Oct 25 '14 at 1:21
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First, don't take that graph too literally, it is just a cartoon version and isn't quantitatively correct.

The USSR heavily subsidized fertilizer until 1988. When they ended the subsidy, fertilizer prices increased to market prices and use of fertilizer decreased. Fertilizer use decreased further after the USSR fell a couple years later.

Fertilizer use in France, Germany, UK and Japan peaked in the 1980s and contributed to the decline.

enter image description here

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