Nitrogen Accumulation and Use by a Young Loblolly Pine Plantation in Southeast Oklahoma: Effects of Fertilizer Formulation and Date of Application

Practices that enhance crop tree nitrogen (N) accumulation and use improve the efficiency of forest fertilization operations. This study was established to explore the N accumulation and use by a young loblolly pine plantation in response to (1) season of fertilizer application, (2) herbaceous vegetation suppression, and (3) fertilizer formulation. Water-soluble and slow-release urea formulations were applied to single-tree plots in January/February, April, June, August, and October of 2001 and 2002. Herbaceous vegetation was suppressed where appropriate with glyphosate. Foliage N accumulation was measured 1 and 2 months after fertilization; N use efficiency was measured 1 year after fertilization. Between 0.3 and 8.0% of applied N was recovered by the foliage within 1 month of application and 7–26% of applied N was used for stem growth within 1 year of application. In both years of this study, summer and fall applications produced the highest N accumulation and use. Suppressing herbaceous vegetation enhanced N accumulation and use when the plantation was 3 years of age (with an average tree height of 6 ft in January 2001). N accumulation and use of slow-release urea was similar to or lower than that of water soluble urea in both years of the study.