Nitrogen Fertilization of Young Yellow Poplar and Loblolly Pine Plantations at Differing Frequencies

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Abstract
Loblolly pine (Pinus taeda L.) and yellow poplar (Liriodendron tulipifera L.) seedlings from 1–10 seedling stock were established in the Tennessee Valley near Oak Ridge and fertilized with 300 kg ha−1 of urea‐N over a period of 3 yr according to two regimes: annually in one spring application (100 kg ha−1) and quarterly (25 kg ha−1 quarter−1). Two plantation blocks for each species, one consisting of seedlings preinoculated with mycorrhizae and one without preinoculation, contained three replicate plots per treatment. Annual fertilization produced greater growth and N recovery in both loblolly pine plantations than did quarterly fertilization, the latter not being significantly different from the controls. Growth responses in yellow‐poplar plantations were less certain and not statistically significant, probably due to moisture stress for this species on this site. There was no evidence of prolonged (> 2 yr) enhancement of soil available N following either quarterly or annual fertilization. Quarterly fertilization produced the earliest and generally the most pronounced increases in soil solution NO−3 concentrations in all cases, followed by annual fertilization and control, respectively. These results, combined with laboratory incubations, indicated that quarterly fertilization benefited the nitrifying bacteria more than the trees on this site, particularly in the case of loblolly pine.
Funding Information
  • U.S. Department of Energy (DE‐AC05840R21400)