NH3 volatilization, soil concentration and soil pH following subsurface banding of urea at increasing rates

Rochette, P., Angers, D. A., Chantigny, M. H., Gasser, M.-O., MacDonald, J. D., Pelster, D. E. and Bertrand, N. 2013. NH₃volatilization, soilconcentration and soil pH following subsurface banding of urea at increasing rates. Can. J. Soil Sci. 93: 261–268. Subsurface banding of urea can result in large ammonia (NH₃) emissions following a local increase in soil ammonium () concentration and pH. We conducted a field experiment to determine how application rates of subsurface banded urea impact NH₃ volatilization. Urea was banded at a 5 cm depth to a silty loam soil (pH=5.5) at rates of 0, 6.1, 9.2, 13.3 and 15.3 g N m⁻¹. Ammonia volatilization (wind tunnels), and soil concentration and pH (0–10 cm) were monitored for 25 d following urea application. Volatilization losses increased exponentially with urea application rate to 11.6% of applied N for the highest urea rate, indicating that as more urea N was added to the soil a larger fraction was lost as NH₃. Cumulative NH₃-N emissions were closely related (R²≥0.85) to maximum increases in soil concentration and pH, and their combined influence likely contributed to the nonlinearity of the volatilization response to urea application rate. However, the rapid increase in NH₃ losses when soil pH rose above 7 suggests that soil pH was the main factor explaining the nonlinear response of NH₃ volatilization. When compared with previous studies, our results suggest that the response of NH₃ volatilization losses to urea application rate in acidic soils are controlled by similar factors whether urea is broadcasted at the soil surface or subsurface banded.