Effects of Temperature and Soil Type on Ammonia Volatilization from Slow-Release Nitrogen Fertilizers

Ammonia (NH3) volatilization is the major pathway for mineral nitrogen (N) loss from N sources applied to soils. The information on NH3 volatilization from slow-release N fertilizers is limited. Ammonia volatilization, over a 78-d period, from four slow-release N fertilizers with different proportions of urea and urea polymer [Nitamin 30L (liquid) (L30), Nitamin RUAG 521G30 (liquid) (G30), Nitamin 42G (granular) (N42), and Nitroform (granular) (NF)] applied to a sandy loamy soil was evaluated. An increase in temperature from 20 to 30 degrees C increased cumulative NH3 volatilization loss in the sandy soil by 1.4-, 1.7-, and 1.8-fold for N42, L30, and G30, respectively. Increasing the proportion of urea in the slow-release fertilizer increased NH3 volatilization loss. At 30 degrees C, the cumulative NH3 volatilization over 78 d from a sandy soil accounted for 45.6%, 43.9%, 22.4%, and 1% of total N applied as N42, L30, G30, and NF, respectively. The corresponding losses in a loamy soil were 9.2%, 3.1%, and 1.7%. There was a significantly positive correlation between NH3 volatilization rate and concentration of NH4-N released from all fertilizers, except for NF (n = 132; r = 0.359, P = 0.017 for N42; r = 0.410, P = 0.006 for L30; and r = 0.377, P 0.012 for G30). Lower cumulative NH3 volatilization from a loamy soil as compared to that from a sandy soil appeared to be related to rapid nitrification of NH4-N in the former soil than that in the latter soil. These results indicate the composition of slow-release fertilizer, soil temperature, and soil type are main factors to dominate NH3 volatilization from slow- release fertilizers.