The effect of air-flow rates on the volatilization loss of NH^ from urea was studied on two soil types. In both soils, the volatilization loss increased with increasing air flow rates up to 14 volume/min. Further increase in air-flow rate to more than 14 volume/min. did not significantly increase volatilization loss of NH3 It is suggested that volatilization loss should be measured at an air flow rate of 14 volume/ min.