The type of synthetic fertilizer used affects the rate of NH₃ lost. Urea fertilizer has been shown to produce the highest emissions of the total available NH₃ at 6–25% (ECETOC 1994), while emission rate for calcium ammonium nitrate is 5–14% (Bussink, 1994), depending on the rate of application. NH₃ emissions are about 20% of the application in dry soil because of diffusion through soil pores, 50% in wet soils because of incomplete closure of injection slits, and insignificant in moist soils (Sommer and Christensen, 1992). The 1990 Canadian inventory in Canada shows that fertilizer application accounts for about 104 ktonnes of NH₃ emissions (Table 2). Early analysis of the 1995 data indicates an in increase in overall emissions of approximately 26% (Environment Canada, 1997). Approximately 11% of nitrogen in fertilizer is converted to NO_x (Shepherd et al., 1991). Fluxes of NO_x from fertilized fields into the atmosphere are strongly related to nutrient levels, soil moisture, and soil temperature (ibid.). There are no reliable estimates for NO_x emissions from soils across Canada.