The Effect of Mid-Rotation Fertilization on the Wood Properties of Loblolly Pine (Pinus Taeda)

Abstract

Mid-rotation fertilization is a common practice in the management of loblolly pine (Pinus taeda L.) plantations, typically providing large improvements in growth. However, concerns exist about the quality of wood produced following fertilization. The objective of this study was to develop an understanding of wood property changes following fertilization. Wood samples from a study involving four levels of fertilization applied to a thinned mid-rotation loblolly pine plantation located on the lower coastal plain of North Carolina were sampled. The study was laid out in a randomized complete block design involving four blocks and four levels of nitrogen fertilizer: Control-000, 112, 224 and 336 kg/ha, along with 28 kg/ha of phosphorus with all treatments. Thirty-two trees were felled and disks were cut at five heights from each tree. Wood properties including modulus of elasticity, air-dry density and tracheid anatomical properties were measured for each of the three post-fertilization annual growth rings using near infrared (NIR) spectra obtained from the radial face of strips cut from the disks. An analysis of variance was conducted on three-year basal area weighted average stiffness, air-dry density, and tracheid anatomical properties. A decrease in stiffness, air-dry density, tracheid wall thickness, and an increase in tracheid radial diameter were observed for the heaviest fertilizer treatment (336 kg/ha) compared to the control and 112 kg/ha of nitrogen. Microfibril angle (MFA), cell tangential diameter, and tracheid perimeter showed little change. Wood properties of trees receiving fertilizer rates of 112 and 224 kg/ha were not significantly affected.