Predicting Fertilizer Response of Loblolly Pine Using Foliar and Needle-Fall Nutrients Sampled in Different Seasons

Abstract

Abstract Nitrogen (N) and phosphorus (P) concentrations in loblolly pine (Pinus taeda) foliage and needle-fall were determined five times during 1979 on ten fertilizer trials installed between 1971 and 1973. Bole volume responses to fertilizers were regressed on initial stand basal area, and the residual errors were used as dependent variables in regressions with the nutrient variables. The only sampling period during which the N response residuals had a significant relation to foliar nutrients was early fall. The needle-fall N/P ratio was significantly related to the N response residuals in late winter, late spring, and early fall. Phosphorus response residuals were significantly related to foliar nutrients during all sampling periods and to needle-fall N/P in all sampling periods except late winter. The maximum R2;, 0.73, was for the regression of the P response residuals versus a foliar N/P ratio in late spring. The N + P response residuals were not significantly related to foliar or needle-fall nutrients. For. Sci. 34(3):698-707.