AMMONIA VOLATILIZATION FROM UREA AND AMMONIACAL FERTILIZERS SURFACE-APPLIED TO WINTER-WHEAT AND GRASSLAND

Ammonia volatilization from urea, diammonium phosphate, ammonium sulph ate and calcium ammonium nitrate surface applied to winter wheat and g rassland was determined with windtunnels. The fertilizers were applied at a rate of 8-12 g N m-2 to plots on a non-calcareous sandy loam. Fi ve experiments were carried out during March to June 1992, each experi ment including 2 to 4 treatments with two or three replications. The d aily ammonia loss rate was measured during 15 to 20 days. Cumulated da ily loss of ammonia from urea followed a,sigmoidal expression, while t he cumulated ammonia loss from diammonium phosphate showed a logarithm ic relationship with time from application. For ammonium sulphate and calcium ammonium nitrate no significant loss could be determined, beca use daily loss of ammonia were at the detection limit of the wind tunn els. Mean cumulated ammonia loss from plots receiving urea, diammonium phosphate, ammonium sulphate and calcium ammonium nitrate were 25%, 1 4%, <5% and <2%, respectively, during a 15-20 day measuring period.