Modeling Response to Midrotation Nitrogen and Phosphorus Fertilization in Loblolly Pine Plantations

Abstract

Abstract Data from a fertilizer response study in loblolly pine (Pinus taeda L.) plantations at different sites in the southeastern United States were used to develop response models for dominant height and basal area following midrotation nitrogen (N) and phosphorus (P) fertilization. Nonlinear regression models developed from the data predict total cumulative response as a function of the interaction of N and P application rates, drainage class of the site, stand conditions when fertilized, and time since fertilization. Stand variables that were found to be significant predictors of response included site index, age, basal area, number of surviving trees, and dominant height at fertilization. Dominant height response was significantly greater on poorly drained sites than on other sites. Basal area response to P was significantly less on poorly drained sites and significantly greater on well drained sites. These models can be coupled with unfertilized baseline models to estimate volume response to midrotation fertilization. South. J. Appl. For. 24(4):207-212.