Effects of Solution Chemistry and Environmental Conditions on Ammonia Volatilization Losses From Aqueous Systems

Abstract Laboratory studies were conducted to explain the wide variation in reported estimates of ammonia volatilization losses from N‐fertilized paddy fields. The ammonia volatilization capacity of a system was found to be equivalent to its alkalinity [NH 3 (aq), HCO 3 2‐ ]. In solutions lacking alkalinity, loss of (NH 4 ) 2 SO 4 was limited, whereas loss of (NH 4 ) 2 CO 3 was essentially complete. Ammonia loss from solution is best described as a consecutive reaction with opposing step. Ammonia volatilization per se followed first‐order reaction kinetics. The rate of ammonia volatilization is thus directly related to the concentration of aqueous ammonia and therefore to the concentration of ammoniacal N and pH. The rate of ammonia volatilization was severely restricted by limiting the movement of air above the water, as is often the case in the laboratory and field studies reported to date. Ammonia volatilization was enhanced by water turbulence and increased exponentially with temperature from almost nil at 0°C to approximately 20 mg N/100 cm 2 /5 hours at 46°C.