Determination and mitigation of ammonia loss from urea applied to winter wheat with N-(n-butyl) thiophosphorictriamide

This study conducted in the Wimmera, a major cropping area in western Victoria Australia, evaluated a backward Lagrangian stochastic (bLs) dispersion model for measuring ammonia (NH3) loss and compared NH3 losses from a wheat crop after top-dressing with urea or “Green Urea”. Green Urea contained 45.8% nitrogen (N) as urea and “Agrotain” (N-(n-butyl) thiophosphorictriamide) @ 5.0 L/t. The two products (80 kg N ha−1) were applied to circular plots of 25 m radius and losses were determined for a period of 23 days using mass balance micrometeorological methods. When the NH3 concentration in the air at the stability independent height, 0.8 m above the crop, was used there was a strong relationship between the vertical flux density of NH3 as determined by the full profile method and that determined by the bLs method (r = 0.86). Rates of ammonia loss from the urea treatment ranged from 0.2 to 2.1 μg N m−2 s−1, while those from the Green Urea treatment never exceeded 0.35 μg N m−2 s−1. Cumulative NH3 losses for the urea and Green Urea treatments were 7.6 kg N ha−1 (9.5% of applied N) and 0.8 kg N ha−1 (1.0% of applied N), respectively. The results indicate that use of Green Urea instead of regular urea in Victorian wheat growing could substantially reduce NH3 emission.