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) loss 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 application (surfaceapplication, incorporation and placement). Coarse pyrites (>-2mm) were not effective in reducing NH₃ loss from urea when surface applied even at the highest ratio of pyrite (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 treatment. 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 pyrite to surface-applied urea (1:1 ratio) decreased the loss to 13.2%. Urea+pyrite placed below the soil surface had the least loss (9.8%). Results indicate that combined application of urea and fine pyrite could reduce NH₃ loss.