Soil Nutrient Availability Following Application of Biosolids to Forests in Virginia. Eduardo C. Arellano and Thomas R. Fox Department of Forestry, Blacksburg, VA 24061, USA. Discussion After fall application of biosolids, there was a significant increase in nitrogen availability in the forest floor and the top 10 cm of mineral soil. Nitrogen availability remained elevated through the first 8 months following the surface application. The spring application of biosolids also increased the available nitrogen in all treatments. The highest biosolids application rates (1600 lbs/acre PAN) more than doubled the level of available N compared to the standard rate (200 PAN). Soil available N following biosolids applications were similar to soil available N following conventional fertilizer applications when similar N rates were applied. For the use and application of biosolids, considerations should include the type of biosolid and application timing. Application rates in forestry sites have been developed from agricultural conventional applications, although site conditions and nutritional demands are different between the two systems. In order to improve biosolids application in forests, additional work on biosolids application rates and timing on nutrient availability, potential of leaching, and volatilization losses is ongoing. Ongoing research activities One year after application soil will be sampled and characterized at different depths and analyzed for macro and micronutrients, and chemical properties. Trees total dbh and height growth, Foliage Area Index and foliage nutrient uptake will be measured after each growing season. We thank Synagro and Washington DC Council of Governments for their cooperation and help on this project. Study Site Characterization The study has been conducted since September 2005, in a 17 years old thinned Loblolly pine plantation, located in Amelia County in the Piedmont of Virginia. The soil are highly eroded with a shallow surface horizon (A), and a deep Argillic horizon. Slopes at this site range from 2% to 5%. TREATMENTS Fall Applications  Control: No Biosolids Application  Lime Stabilized (800 lbs/ac PAN)  Anaerobically Digested (800 lbs/ac PAN) Spring Applications  Lime Stabilized (200 lbs/ac PAN)  Anaerobically Digested (200 lbs/ac PAN)  Anaerobically Digested (800 lbs/ac PAN)  Anaerobically Digested (1600 lbs/ac PAN)  Pellets (200 lbs/ac PAN)  Urea + DAP (200 lbs/ac Total N)  Lime Stabilized source from Alexandria, Virginia treatment plant  Anaerobically Digested from Blue Plain, Washington DC and Baltimore treatment plant  Biosolid Pellets Commercially available (Granulite®) Problem Statement Forestland in the Piedmont and Upper Coastal Plain of Virginia provides a good alterative location for land application of biosolids. Effective specific design criteria are required for successful forestland application systems. Issues such as loading rate, nutrient assimilation rates in the ecosystem, nutrient losses, and growth response for various types of biosolids must be addressed. It may not be possible to simply extrapolate agricultural land application practices to forest settings. Objectives The objectives of this field study are 1) to quantify changes in nutrient availability and cycling in a Loblolly pine (Pinus taeda L.) plantation following the application of conventional fertilizer and three types of biosolids (lime stabilized, anaerobically digested, and pelletized) at two different times of the year (fall vs spring), and 2) determine the impact of biosolids application on growth of loblolly pine. Study Design and methods The study was established as a random complete block design with nine treatments of various biosolids types surface applied at two times during the year. Nine different treatments (Control, anaerobically digested and lime stabilized biosolids during the fall, digested in spring (3 rates), lime stabilized, urea + DAP, and biosolid pellets) were applied in 36 plots. Biosolids were fully characterized before and during surface application to fully understand nutrient content Application rates were determined based on plant available nitrogen (PAN) using the Virginia Department of Health recommendations (1997). The Fall treatments were applied on November The Spring treatments were applied during March Ion exchange membranes were used to determine changes in available PO 4, NO 3 and NH 4 in the forest floor and top 10 cm of the mineral soil. Results Results from the ion exchange membranes, indicate that biosolids and conventional fertilization increased soil nitrogen availability after surface application in both the fall and the spring. However, nitrogen availability increased more rapidly following the fall application compared to the spring application. Acknowledgments Table 1: Biosolids Characterization BIOSOLIDS SURFACE APPLICATION ION EXCHANGE MEMBRANES 17 yrs old Loblolly Pine Plantation Amelia County (Virginia Piedmont)