AMMONIA VOLATILIZATION FROM SOIL IRRIGATED WITH URBAN SEWAGE EFFLUENT

Losses of ammonia (NH3) following sewage effluent irrigation of pastur e were measured under different climatic conditions at Wagga Wagga, Ne w South Wales. Ammonia volatilisation was measured by the micrometeoro logical mass balance technique using 2 different passive samplers, and by an indirect technique based on the measurements of ammoniacal-N (N H4++NH3) concentration, pH, and temperature of the soil solution in th e 0-3 mm soil layer, and wind speed at 1.2 m above the soil surface. M aximal NH3 emission rates were measured directly following the effluen t-irrigation. There was reasonable agreement between the 2 different p assive gas samplers used to measure NH3 volatilisation. The NH3 volati lised was well related to the product of wind speed and the equilibriu m ammonia concentration (calculated from the soil solution measurement s) as was found in other studies. In addition, NH3 flux density was st rongly related to evaporation; that is, when the water (effluent) evap orated NH3 was lost to the atmosphere. Under high evaporative conditio ns, a maximum of 24% of the ammoniacal-N in the effluent was lost by v olatilisation within 2 days of application.