Response of Densely Stocked Loblolly Pine (Pinus taeda L.) to Applied Nitrogen and Phosphorus

Abstract

Abstract Forest productivity may be enhanced by satisfying the nutrient requirement of trees through fertilization. A field experiment was designed to study the response of densely stocked 1-yr-old loblolly pine to nitrogen and phosphorus in the presence of applied K on a Beauregard silt loam soil (fine-silty, siliceous, thermic Plinthaquic Paleudults) of the Gulf Coastal Plain. The continuous function design with three replications was used. Fertilizer P rate was based on the P adsorption characteristics of the soil. After 1 yr of growth, the response variables: height; total aboveground dry matter; foliage and wood dry matter; diameter at ground level; and N, P, and K contents were related to the rate of N and P applied by quadratic models with response surface methodology. The lack-of-fit test showed that the quadratic model was adequate in explaining the relationship between N and P applied and all the response variables except height. Fertilization with N alone on this soil had a depressing effect on yield. Growth and nutrient uptake were enhanced when both N and P were applied. The predicted N and P levels that would give maximum growth were beyond the rates of N and P tested, indicating that more time should be given to observe the full response. South. J. Appl. For. 27(3):180–189.