Effects of Urea Fertiliser Type, Urease Inhibitor (Agrotain), Application Method and Season On Ammonia Loss From Ryegrass.

Ammonia (NH₃) loss from granular urea surface applied to pastures in Australia can be high, with reported emissions of up to 25% of applied N. Application of urea 1) treated with a urease inhibitor (N-(n-butyl) thiophosphorictriamide (NBPT)) or 2) applied as a fine particle  spray are two methods that can be used to reduce loss. A field experiment was conducted to measure the reduction in NH₃ loss from ryegrass (Lolium perenne L) in southeastern Australia in two seasons (autumn and spring)  using Green Urea 14 (urea coated with a urease inhibitor,  NBPT, and  urea ammonium nitrate (UAN) surface applied, and “Nhance”, a fine particle spray containing NBPT and giberillic acid, compared to granular urea. A micrometeorological technique was used to measure NH₃ loss.

Ammonia loss from granular urea was 30% of applied N in autumn. Use of Green Urea and the fine particle spray treatments instead of granular urea reduced NH₃ loss in autumn to 9% and 23%, respectively. In spring, rainfall within 24 hours of fertiliser application resulted in low loss of NH₃) from the granular urea and Green Urea (2% and 1% of applied N, respectively). Application of UAN (in solution) instead of granular urea had no impact on NH₃ volatilisation. Biomass production did not reflect the savings in N as a consequence of reduced NH₃ loss.