Ammonia Volatilization Following Banding of Urea to Eight Agricultural Soils.

In acidic soils, ammonia volatilization can be increased when urea is incorporated in bands compared to incorporation following a broadcast application. A study was conducted to determine the influence of soil properties and soil genesis on the impact of banding of incorporated (5 cm) urea on ammonia emissions. Eight surface soils with pH between 5 and 6 and with contrasting properties, including coarse to fine texture, buffering capacity and CEC, were sieved to 2 mm and repacked in cylinders (i.d., 20-cm) and in shallow (10 cm) containers (width, 60 cm; length, 100 cm). Cylinders were incubated during 30 days in dynamic open chambers to measure ammonia volatilization while containers were sampled periodically to monitor changes in soil pH, urease activity and mineral N content. Soil pH increased up to 8.5 and ammonium N contents increased several fold in all soils as a result of the hydrolysis of urea in the band. However, ammonia emissions were only observed in coarsed-texture soils where cumulative losses reached 10% of added N. Our results suggest that the impact of banding urea on ammonia volatilization is strongly influenced by soil texture with significantly greater emissions in coarser texture soils.