Nitrogen: The historical progression from ignorance to knowledge, with a view to future solutions

Once upon a time there was enough naturally occurring nitrogen (N) to provide food for the world's peoples. Then there was not in the western regions. Now there is due to industrially produced NH3. But this transition from plenty, to scarcity, to plenty has come with a tremendous environmental cost. This paper provides an historical overview of the growth of knowledge about N and about its impacts, both positive and negative. The paper also explores three scenarios of what might have been, if in 1700 the world had the N-knowledge that we have now. The paper then projects N use to feed the world's people in 2050 under three scenarios of per-capita protein consumption: increasing, constant and decreasing relative to nutritional guidelines. The three projected results for 2050 annual N use from producing and consuming food are 320, 230 and 170 Tg N respectively. The latter is equivalent to 1970 levels. Given that the first scenario (increasing protein) is most likely without utilising our N-knowledge, the paper ends with suggestions for improvements in N use and management