Ammonia Volatilization Following Nitrogen Fertilization with Enhanced Efficiency Fertilizers and Urea after a Spring, Summer and Winter Fertilization in Loblolly Pine (Pinus taeda L.) Plantations of the Southern United States.

Ammonia (NH₃) volatilization losses following surface application of urea and enhanced efficiency (CUF, NBPT, PCU) nitrogen (N) containing fertilizers (EEFs) were compared in two different studies (Study 1, 2) in thinned mid-rotation loblolly pine stands (Pinus taeda L.) across the southern United States. All fertilizer treatments for both studies were labeled with ¹⁵N (~370 permil, 0.5 AP) and applied to individual open chamber microcosms, and losses of fertilizer N were determined using a mass balance calculation. Study 1 was installed in 2011 at six sites with fertilizer treatments applied during two different seasons (spring, summer) to microcosms sampled 1, 15 and 30 days after fertilization. In Study 1, significantly less fertilizer N loss occurred following fertilization with EEFs compared to urea after all sampling days for both seasons. There were generally no differences among the individual EEFs. Following spring application, the mean NH₃ volatilization during the 30 day experiment ranged from 4% to 26% for the EEFs compared to 26% to 40% for urea. In summer, mean NH₃ volatilization for EEFs ranged from 8% to 23% compared to 29% to 49% for urea. Study 2 was installed in the winter of 2016, and assessed differences in fertilizer N loss between urea and NBPT at three sites after 15 days. A difference occurred between the two treatments in Study 2 where more fertilizer N was recovered from the NBPT treatment compared to urea. Because root uptake was eliminated in the microcosms and there was no leaching of ¹⁵N below the microcosms, the most likely loss pathway of the ¹⁵N from the microcosms was NH₃ volatilization. This research highlights the potential of EEFs to reduce loss of fertilizer N in forest systems, potentially increasing fertilizer N use efficiency in these pine plantations.