AMMONIA VOLATILIZATION FROM UREA AS AFFECTED BY THE ADDITION OF IRON PYRITES AND METHOD OF APPLICATION

Laboratory incubations were conducted to determine the ammonia (NH3) l oss from urea as affected by the addition of coarse and ground (fine) pyrites at 1:1, 1:2 and 1:5 urea: pyrite (w/w) ratios and methods of a pplication (surface-application, incorporation and placement). Coarse pyrites (greater than or equal to 2mm) were not effective in reducing NH3 loss from urea when surface applied even at the highest ratio of p yrite (15.9% vs 18.7% without pyrite). Ground pyrites (0.1 - 0.25 mm), in 1:1 ratio, had about 5% less NH3 loss than the urea alone treatmen t. Higher ratios of pyrites reduced NH3 loss much more. Ammonia losses were the most with surface-applied urea (18.9%) and the least (13.5%) when placed (2.5 cm) below the soil surface. Addition of ground pyrit e to surface-applied urea (1:1 ratio) decreased the loss to 13.2%. Ure a+pyrite placed below the soil surface had the least loss (9.8%). Resu lts indicate that combined application of urea and fine pyrite could r educe NH3 loss.