1. Alexander, R. B. and Smith, R. A.: County level estimates of nitrogen and phosphorus fertilizer use in the United States, 1945 to 1985, U.S. Geological Survey, Books and Open-File Reports [distributor] No. 90-130, Reston, Virginia, USA, 1990.
2. Alexandratos, N. and Bruinsma, J.: World agriculture towards 2030/2050: the 2012 Revision, ESA Working paper No. 12-03, FAO, Rome, Italy, 2012.
3. Association of American Plant Food Control Officials (AAPFCO): Commercial Fertilizers (1986, 1996, 2006, 2012), available at: http://www.aapfco.org/publications.html, last access: 19 November 2017.
4. Azam, F., Müller, C., Weiske, A., Benckiser, G., and Ottow, J.: Nitrification and denitrification as sources of atmospheric nitrous oxide-role of oxidizable carbon and applied nitrogen, Biol. Fert. Soils, 35, 54–61, 2002.
5. Beddow, J. M.: A bio-economic assessment of the spatial dynamics of US corn production and yields, PhD thesis, University of Minnesota, Minneapolis, Minnesota, USA, 2012.