Soil properties that influence ammonia loss from surface‐applied, unincorporated urea‐based fertilizer

Abstract The composition and breakdown paths of urea ammonium nitrate (UAN) and urea are different, but there is limited information on how soil properties relate to ammonia volatilization loss from surface‐applied, unincorporated UAN and urea on various soils. Controlled environment incubation experiments were conducted to evaluate ammonia volatilization potential of commonly used urea‐containing fertilizers, and to correlate these losses to selected soil properties. A completely randomized design with four replicates was used to evaluate and correlate ammonia loss from urea and UAN applied onto eight soils at a rate of 134 kg N ha −1 . Urea was more susceptible to ammonia loss (21% of applied N) than UAN (3.3% of applied N) in soils with pH < 7. In contrast, the losses from UAN were either higher or comparable to urea for soils with pH > 7. A significant and strong relationship was evident between ammonia loss from UAN and soil pH ( R 2 = 0.84), soil organic matter ( R 2 = 0.65), clay content ( R 2 = 0.69), and container capacity ( R 2 = 0.90). In contrast, the loss relationships observed for the urea and these properties were insignificant. Stepwise regression analysis identified clay content and soil pH as the most influential factors affecting ammonia loss from both urea and UAN applications. In conclusion, high initial soil pH significantly increases ammonia loss for surface‐applied UAN but not for urea, suggesting that different soil management strategies may be needed depending on the N fertilizer source used.