1. Lehnert, N., Coruzzi, G., Hegg, E., Seefeldt, L. & Stein, L. NSF Workshop Report: Feeding the World in the 21st Century: Grand Challenges in the Nitrogen Cycle (National Science Foundation: Arlington, VA, 2016).
2. Canfield, D. E., Glazer, A. N. & Falkowski, P. G. The evolution and future of earth’s nitrogen cycle. Science 330, 192–196 (2010).
3. Galloway, J. N. et al. Transformation of the nitrogen cycle: recent trends, questions, and potential solutions. Science 320, 889–892 (2008).
4. Fields, S. Global nitrogen: cycling out of control. Environ. Health Perspect. 112, A556–A563 (2004).
5. Smil, V. Nitrogen cycle and world food production. World Agric. 2, 9–13 (2011).