Can soil clay content predict ammonia volatilization losses from subsurface-banded urea in eastern Canadian soils?

To determine how soil physical and chemical characteristics affect NH3 volatilization, we measured NH3 losses from eight different eastern Canadian soils with various soil clay contents and cation exchange capacities (CEC). Losses were measured from soil mesocosms banded (0.05 m depth) with urea (equivalent of 140 kg N ha−1) in a dynamic chamber system fitted with an acid trap; with soil properties measured in parallel mesocosms. Regression analysis indicated a negative relationship between 28 d of NH3 volatilization losses and soil clay content (P < 0.001; R2 = 0.978), CEC (P < 0.001; R2 = 0.941), and buffer capacity (P = 0.006; R2 = 0.772), and positive relations with maximum change in soil pH (P = 0.015; R2 = 0.670) and maximum water-extractable NH4+ (P = 0.010; R2 = 0.721). A 90% reduction in NH3 losses occurred when clay content increased from 10% to 20%. Also, the correlation between water-extractable NH4+ and NH3 loss and a lack of correlation between salt-extractable (1 mol L−1 KCl) NH4+ and NH3 loss indicate that NH4+ bound to cation exchange sites does not contribute to the rapid NH3 volatilization. However, more research on soils of different mineralogy is required to ascertain whether this holds in other regions as well.