Abstract

Losses of fertilizer nitrogen (N) were compared between urea and urea treated with the urease inhibitor N-(n-Butyl) thiophosphoric triamide (urea + NBPT) after a surface application in winter at three thinned mid-rotation (age 15-20 years) loblolly pine plantations in Virginia, South Carolina, and Florida. Treatments were labeled with N-15 and applied to open chamber microcosms in January and February 2016. Fifteen days after application, microcosms were removed from the field to determine fertilizer N lost from each microcosm. Losses following fertilization with urea (24% to 50%) were greater (p >= .05) at all sites compared to urea + NBPT (12% to 22%). Fertilizer N losses were greater in Florida than in SC and Virginia although N loss following urea fertilization was still 25% in Virginia. The loss of fertilizer N was consistently lower on beds compared to interbeds for both urea (bed = 25%, interbed = 40%) and urea + NBPT (bed = 12%, interbed = 23%). This research highlights the value of using urea + NBPT to reduce fertilizer N losses after a winter application and the greater potential loss in the interbed on wetter sites.