Factors Contributing to Variability in Loblolly Pine Foliar Nutrient Concentrations

Variability in loblolly pine (Pinus taeda) foliar nutrient concentrations was partitioned into field sampling and laboratory components using data from 43 midrotation, site-prepared stands in the southeastern United States. Foliar nutrient concentrations were normally distributed; N and P concentrations averaged 1.06% and 0.100%, respectively. Coefficients of variation (CV) for individual studies ranged from 3.4 to 8.5% for N and 3.7 to 12.2% for P. Accuracy and precision of nutrient determinations exhibited practical and statistical variability among laboratories examined; average CV ranged from 1.6 to 6.9% for N and from 1.2 to 17.9% for P. A majority of laboratories achieved percent recovery [(observed ÷ known) x 100] ± 5% and CV ≤ 5% for most elements, suggesting these levels are achievable given present quality assurance (QA) technology. Field sampling accounted for 71 and 86% of the total variation in foliar N and P concentrations, respectively. Field sampling guidelines suggested to reduce the introduction of extraneous variation include careful attention to sampling season, crown class and position, foliage age, and growth flush. South. J. Appl. For. 20(1):45-52.