Ammonia volatilisation from soil irrigated with urban sewage effluent

Abstract

Losses of ammonia (NH₃) following sewage effluent irrigation of pasture were measured under different climatic conditions at Wagga Wagga, New South Wales. Ammonia volatilisation was measured by the micrometeorological mass balance technique using 2 different passive samplers, and by an indirect technique based on the measurements of ammoniacal-N (NH₄⁺ + NH₃) concentration, pH, and temperature of the soil solution in the 0–3 mm soil layer, and wind speed at 1.2 m above the soil surface. Maximal NH₃ emission rates were measured directly following the effluent-irrigation. There was reasonable agreement between the 2 different passive gas samplers used to measure NH₃ volatilisation. The NH₃ volatilised was well related to the product of wind speed and the equilibrium ammonia concentration (calculated from the soil solution measurements) as was found in other studies. In addition, NH₃ flux density was strongly related to evaporation; that is, when the water (effluent) evaporated NH₃ was lost to the atmosphere. Under high evaporative conditions, a maximum of 24% of the ammoniacal-N in the effluent was lost by volatilisation within 2 days of application.