Ammonia Volatilization Following Fertilization with Urea or Ureaform in a Thinned Loblolly Pine Plantation

Volatilization losses following fertilization with urea or ureaform applied at a rate of 448 kg ha(-1) N were measured in a thinned 22-yr-old loblolly pine (Pinus taeda L.) plantation in the Virginia Piedmont. Fertilizer was applied at two different times, winter and summer, and NH3 volatilization was measured for 29 d using a static chamber method. The majority of the NH3 volatilization occurred during the first 7 to 9 d following fertilization. Larger amounts of NH3 were volatilized following fertilization with urea than with ureaform. Following application in the summer, 51% of the applied N was volatilized from urea while only 7% of the applied N was volatilized from ureaform. The amount of N volatilized following urea application in the winter was 18% compared to 11% following ureaform application. This study highlights the risks of N loss through volatilization associated with urea fertilization, especially when it is applied during the growing season. These results also indicate that slow release N fertilizers such as ureaform can decrease volatilization losses following surface application in loblolly pine forest ecosystems and may, therefore, increase N uptake by the trees.