Abstract Ammonia volatilization is an important mechanism of nitrogen (N) loss from soils which is dependent on several soil and management factors. This research was conducted with Biscayne Marl Soil and Krome Gravelly Loam from Florida and Quincy Fine Sand and Warden Silt Loam from Washington to determine ammonia volatilization at various temperature and soil water regimes using either potassium nitrate (KNO3), ammonium nitrate (NH4NO3), ammonium sulfate ((NH4)2SO4) or urea applied to the soil at 75 kg N ha-1 rate. Soil water regime was maintained at either 80% or 20% of field capacity, and incubated at either 11, 20 or 29 oC which represent the minimum, average and maximum temperatures, respectively, during potato growing season in Washington. Results indicated that the ammonia volatilization rate at 20% FC soil water regime was 2- to 3-fold greater than that at 80% FC. The cumulative volatilization loss over 28 days accounted for 0.21% (Warden Silt Loam) to 13.09% (Krome Gravelly Loam) loss of N applied as NH4NO3. This loss increased to 0.34% (Warden Silt Loam) to 25.71% (Krome Gravelly Loam) for (NH4)2SO4. Results of this study demonstrate that NH3 volatilization was accelerated at low soil water regimes. Thus, maintaining near optimum soil water regime is important to minimize volatilization loss of N and to improve N uptake efficiency in addition to its direct effects on plant growth and nutrient uptake. Key words: ammonia volatilization; field capacity; temperature; potato