Effects of form of nitrogen, season, and urea application rate on ammonia volatilisation from pastures

Abstract

Ammonia (NH₃) volatilisation from various nitrogenous (N) fertilisers broadcast at different times of year on to pasture at a rate of 3 g/m² N (30 kg/ha N) was measured by an enclosure method. The average percent losses of NH₃-N were: urea, 11.9; diammonium phosphate, 5.3; ammonium sulphate, 1.0; and calcium ammonium nitrate, 0.8. Loss from sulphur-impregnated urea was equal to, or slightly less than that from urea. The loss was positively related to the maximum soil surface pH produced by each of the fertilisers. No seasonal pattern was observed, except that NH₃ loss tended to be lower in August–September. The loss from urea increased from 13 to 33% of N applied as the application rate increased from 3 to 20 g/m² N (30–200 kg/ha N).