1. Estimated 115 Tg N/year N feritilizer applied globally (2018). Food and Agriculture Organization of the United Nations (2016) World Fertilizer Trends and Outlook to 2020: Summary Report (http://www.fao.org/3/a-i6895e.pdf).
2. Global agriculture and nitrous oxide emissions
3. Agroecosystems, Nitrogen-use Efficiency, and Nitrogen Management
4. The number is based on fertilizer cost and use for corn farming in Illinois USA 2015.http://farmdocdaily.illinois.edu/2015/12/current-fertilizer-prices-and-projected-2016-costs.html.