Effect of Mid-Rotation Fertilization on Stiffness and Strength of Loblolly Pine Wood

Abstract

Trees sampled from a loblolly pine mid-rotation fertilization trial were used in this study. The study was laid out in a randomized complete block design with four levels of nitrogen fertilizer as treatments: control (000N), 112 (112N), 224 (224N), and 336 (336N) kg/ha of nitrogen, with each treatment replicated in 4 blocks. Two trees were destructively sampled from each plot giving a total of 32 trees. Bolts 0.6 m in length were collected from each tree (3 bolts per tree); with the midpoint of each bolt at heights of 2.4, 7.3 and 12.2 m from the base of the tree (each bolt represented the midpoint of standard 4.9 m saw logs). Static bending samples with dimensions 25 by 25 by 406 mm (radial, tangential and longitudinal dimensions respectively) were cut from the bolts that included the 25 mm of wood produced immediately following fertilization. Data on modulus of elasticity (MOE, stiffness) and modulus of rupture (MOR, strength) were collected from clear static bending samples. Based on the analysis of variance, no significant treatment effect was observed on MOE and MOR. However, MOE and MOR decreased in wood produced immediately after fertilization for trees which received the highest level of fertilization (336N). A decreasing trend in MOE and MOR with height was also present.