7Stewart W M, Dibb D W, Johnston A E, Smyth T J. The contribution of commercial fertilizer nutrients to food production. Agronomy Journal, 2005, 97(1): 1-6.
9Erisman J W, Sutton M A, Galloway J, Klimont Z, Winiwarter W. How a century of ammonia synthesis changed the world. Nature Geoscience, 2008, 1(10): 636-639.
10Vitousek J P W, Abet J D, Howarth R W, Likens G E, Matson P A, Schindler D W, Schlesinger W H, Tilman D G. Human alteration of the global nitrogen cycle: sources and consequences. Ecological Applications. 1997, 7(3): 737-750.
