Thursday, November 16, 2006 - 11:00 AM

Long-Term Effects of P Fertilization and Silvicultural Treatments on P Pools and Labile P in Loblolly Pine Plantation Soils.

Bradley Miller and Tom Fox. Virginia Polytech, 210 Chrisman St, Christiansburg, VA 24073

Phosphorus (P) is one of the most limiting nutrients in forest soils. Phosphorus fertilization increases plant available or “labile” P after fertilization; however it is uncertain how P fertilization influences organic and inorganic P pools over the long term in forest soils. Site specific properties such as above- and belowground biota, soil organic matter, and mineralogy can have large influences on P availability. The goal of this project is to determine how site preparation, vegetation control, and fertilization affect P pools twenty years after fertilization at four sites in the southeastern US. Stratified soil samples were collected down one meter deep in P. taeda plantations established on well- and poorly drained sandy and clay soils subjected to low and high intensity site preparation. Phosphorus pools were quantified using the Hedley sequential fractionation procedure, Mehlich-1, and Mehlich-3 soil tests. The Hedley fractionation procedure delineates the total soil P into inorganic and organic pools; labile P, moderately labile P, recalcitrant P, and total P pools. Total soil C was measured using a LECO CR-12 carbon system. Soil C content significantly increased in the fertilized sites. Mehlich-3 P was significantly higher in the fertilized sites compared to control sites. Fertilization increased the Hedley total P and moderately labile inorganic and organic P regardless of site preparation intensity and drainage class compared to unfertilized soils. Organic P pools decreased with depth from the soil surface. After twenty years, labile P pools remained significantly higher in fertilized plots compared to controls in sandy coastal plains soils. The labile P pools in the fertilized plots increased but were smaller on the well drained sites. Results from this research will help our understanding on the long-term affects of forest fertilization prescriptions on P pools.