Table 3.

Ammonia volatilization as a percentage of N application rate with different fertilization methods, crops, N rate and N source

Fertilization methods	Cropa	N rate (kg N ha−1)	NH3 volatilization (%)	N source	References
Surface-broadcast	M	–	30	Urea	Zhang et al. (1992)
	M	186	25	Urea	Li et al. (2002a)
	M	148	37	Ammonium bicarbonate	Li et al. (2002a)
	M	157	27	Urea	Zhang et al. (2005)
	W	110	15	Urea	Zhang et al. (2005)
	W	150	24	Urea	Zhang et al. (2005)
Broadcast before irrigation or plowing, or point deep-placed	W	191–210	10–12	Ammonium bicarbonate	Li et al. (2002b)
	W	300	19	Urea	Li et al. (2002b)
	M	300	25	Urea	Li et al. (2002b)
	M	50–117	27	Urea	Su et al. (2007)
	W–M	–	24–37	Urea	Su et al. (2007)

^aW, M and W–M is wheat, maize, and wheat-maize systems, respectively