Understanding the Fate of Applied Nitrogen in Pine Plantations of the Southeastern United States Using 15N Enriched Fertilizers

This study was conducted to determine the efficacy of using enhanced efficiency fertilizer (EEFs) products compared to urea to improve fertilizer nitrogen use efficiency (FNUE) in forest plantations. All fertilizer treatments were labeled with ¹⁵N (0.5 atom percent) and applied to 100 m² circular plots at 12 loblolly pine stands (Pinus taeda L.) across the southeastern United States. Total fertilizer N recovery for fertilizer treatments was determined by sampling all primary ecosystem components and using a mass balance calculation. Significantly more fertilizer N was recovered for all EEFs compared to urea, but there were generally no differences among EEFs. The total fertilizer N ecosystem recovery ranged from 81.9% to 84.2% for EEFs compared to 65.2% for urea. The largest amount of fertilizer N recovered for all treatments was in the loblolly pine trees (EEFs: 38.5%–49.9%, urea: 34.8%) and soil (EEFs: 30.6%–38.8%, urea: 28.4%). This research indicates that a greater ecosystem fertilizer N recovery for EEFs compared to urea in southeastern pine plantations can potentially lead to increased FNUE in these systems.