Old-field longleaf pine (Pinus palustris Mill.) long-term growth and yield response to midrotation fertilization

Abstract

Longleaf pine (Pinus palustris Mill.) is frequently planted on former agricultural fields throughout the southeastern United States. Limited information is available on the long-term growth and yield as well as stem quality of longleaf pine growing on these sites with and without midrotation fertilization. The objectives of this study were (1) to determine the growth rates, wood yields, and stem quality of old-field longleaf pine and (2) to quantify growth improvements provided by midrotation fertilization. Study sites were established on former agricultural fields in Screven and Tift County, Georgia in unthinned longleaf pine stands planted during December 1986. Three treatments including a control, single full dose, and split dose of nitrogen, phosphorus, and potassium were applied prior to thinning. Assessments of diameter at breast height, height growth, volume, green weight, and basal area at both sites were conducted at ages 21, 23, 27, 30, and 32. After 32 years, results indicated no statistically significant improvements of any growth parameters compared to the control in relation to midrotation fertilization treatments, and stem defects occurred in approximately 29-35 percent of trees. The fast growth rate and low nutrient demand of longleaf pine on these sites obviate the need for midrotation fertilization. Study Implications: Longleaf pine has been extensively planted on former agricultural sites throughout the southeastern United States. Former agricultural fields where new longleaf pine stands are often established usually have moderate to high residual soil fertility. Longleaf pine growth rates may not respond positively to midrotation fertilization applications as has often been reported with other southern pine species. In addition, longleaf pine planted on old-field sites appears to have high stem defect rates, which is not a direct result of fertilization. Landowners and practitioners should carefully consider using soil and foliage nutrient tests as diagnostic tools for midrotation fertilization decisions.