6Smil V. Enriching the earth: fritz haber, carl bosch, and the transformation of word food production [ M ]. Cambridge: MIT Press, 2001. 102-113.
7Ju X T, Xing G X, Chen X P. Reducing environmental risk by improving N management in intensive Chinese agricultural systems[J]. PNAS, 2009, 106(9) : 3041-3046.