Ammonia Volatilization From Banded Urea: Impact of Application Rate and Depth of Incorporation.

Soil incorporation of urea in narrow bands can result in large ammonia emissions following a local increase in soil pH induced by urea hydrolysis. We conducted two field experiments to determine the impact of urea concentration in the band and the depth of urea placement on ammonia volatilization. Volatilization was negligible when urea was incorporated at 7.5 and 10 cm depths, weak at 5 cm (7% of applied urea-N), high at 2.5 cm (37%) and highest for surface banding (50%). Ammonia-N losses were proportional to changes in soil pH and NH-N concentrations in the surface 2 cm above the banded urea, clearly showing that banded urea can lead to ammonia volatilization by influencing the vertical soil pH and NH4-N concentration. Volatilization losses also increased with the rate of urea application when placed at 5 cm, especially at rates above 120 kg Nha-1.