Saturday, 15 July 2006

The long-term effects of a single phosphorus fertilizer application on phosphorus availability in forest soils.

Bradley W. Miller, Virginia Tech, Department of Forestry, 228 Cheatham Hall, Blacksburg, VA 24061 and Thomas Fox, Virginia Tech University, 228 Cheatham Hall, Blacksburg, VA 24061.

Phosphorus (P) is one of the most limiting nutrients in forest soils. The concentrations of inorganic P in soil solutions are low because P is rapidly sorbed to soil colloids. 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. Soil samples were collected to one meter in loblolly pine 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 for noncalcareous soils. This procedure determined total P, “labile” P, “moderately labile” P, and recalcitrant P pools. Fertilization increased levels of total P regardless of site preparation intensity and drainage class compared to unfertilized soils. After twenty years, labile P pools remained significantly higher in fertilized plots compared to controls in sandy coastal plains soils. Results from this research will help our understanding on the long-term affects of forest fertilization prescriptions on P pools. Implications of this research suggest that historical applications of P fertilizers in the southeastern US can have long-term effects on labile P pools.

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