Jeq50244 837..848

Forestland application of poultry manure offers an alternative to the conventional practice of pastureland application. Before such a practice is considered viable, however, it must be demonstrated that the forest ecosystem is capable of absorbing the nutrients contained in poultry manure, especially nitrogen (N) and phosphorus (P). From the forestry perspective, it must also be demonstrated that tree growth is not diminished. We investigated these questions using loblolly pine (Pinus taeda L.) stands growing in central Mississippi in an area of high poultry production. Stockpiled broiler litter was applied to newly thinned, 8-yr-old stands at 0, 4.6, and 18.6 dry Mg ha, supplying 0, 200, and 800 kg N ha and 0, 92, and 370 kg P ha, respectively. Levels of nitrate in soil water, monitored at a 50-cm depth with porous cup tension lysimeters, exceeded 10 mg N L during the first two years after application in the 18.6 Mg ha rate but only on two occasions in the first year for the lower rate of application. Phosphate was largely absent from lysimeter water in all treatments. Other macronutrients (K, Ca, Mg, S) were elevated in lysimeter water in proportion to litter application rates. Soil extractable nitrate showed similar trends to lysimeter water, with substantial elevation during the first year following application for the 18.6 Mg ha rate. Mehlich III– extractable phosphate peaked in excess of 100 mg P g soil during the third year of the study for the 18.6 Mg ha rate. The 4.6 Mg ha rate did not affect extractable soil P. Tree growth was increased by the poultry litter. Total stem cross-sectional area, or basal area, was approximately 20% greater after 2 yr for both rates of litter application. Overall, the nutrients supplied by the 4.6 Mg ha rate were contained by the pine forest and resulted in favorable increases in tree growth. The higher rate, by contrast, did pose some risk to water quality through the mobilization of nitrate. These results show that, under the conditions of this study, application of poultry litter at moderate rates of approximately 5 Mg ha to young stands of loblolly pine offers an alternative disposal option with minimal impacts to water quality and potential increases in tree growth. WATER POLLUTION from excess nutrients is of great current concern throughout the world. The principal problems are ground water contamination by N, as NO3, and surface water eutrophication by N and P in various forms (Daniel et al., 1998; Sims and Wolf, 1994). Intensive and concentrated animal production has been implicated as a significant threat to both water quality problems but especially to eutrophication (Mallin, 2000). In the case of poultry production, animal waste has traditionally been applied to pasturelands with little environmental concern. However, as demand for poultry products increases and pasturelands become nutrient saturated, water quality concerns are being reported (Gallimore et al., 1999; Sauer et al., 1999; Vervoort et al., 1998). Forestland offers an attractive alternative to the conventional practice of pastureland application. Several advantages exist. First, poultry production facilities are often located in rural areas with abundant forestland within range of economic transport of poultry waste. Most of the top poultry-producing counties of the Southern United States also have an abundance of southern pine forests (Fig. 1). Second, forests are frequently nutrient limited and routinely fertilized with N and P (Binkley et al., 1999). Third, actively growing forests have an immense potential for rapid nutrient uptake (O’Neill and Gordon, 1994), immobilization (Vitousek et al., 1992), and sediment trapping (Taylor et al., 1990). Previous studies in the southeastern United States have observed promising growth responses of forests to poultry litter application (Samuelson et al., 1999); however, little information exists about the degree to which these forest ecosystems retain the associated nutrients and prevent eutrophication. Trees absorb nutrients in direct proportion to their growth rate (Coleman et al., 1998; Ingestad, 1982). However, forests have additional mechanisms for nutrient retention such as immobilization (Vitousek et al., 1992) and retention of ions on the soil exchange complex (Pritchett and Fisher, 1987). Forest ecosystems are highly buffered with respect to the amount of nutrients lost to stream or ground water after nutrient addition. With the exception of forests saturated with N due to atmospheric deposition and low soil buffering capacity, fertilized forests generally release minimal N or P to streamwater (Binkley et al., 1999). In the Pacific Northwest, large applications of N (700 kg N ha) and P (500 kg P ha) to Douglas-fir [Pseudotsuga menziesii (Mirbel) (Franco)] stands in the form of municipal biosolids resulted in minimal impacts to streamwater quality (Grey and Henry, 2002). Biologically available P, PO4–P, and NH4–N were the same before and after biosolids application. Nitrate N, while doubled in association with the application, was less than 1 mg N L or one-tenth of the USEPA standard for drinking water. In summary, established, fast-growing forests have a large potential for retaining nutrients, especially when applied as biosolids. We anticipated that poultry manure could be applied to pine forests at rates in excess of tree growth demands due to the high potential of forests to retain nutrients. Two concerns shed doubt on this potential, however. First is the concern that large amounts of inorganic N in poultry litter would lead to more N leaching than the A.L. Friend, USDA Forest Service, North Central Research Station, 410 MacInnes Drive, Houghton, MI 49931; S.D. Roberts and J.A. Mobley, Department of Forestry, Mississippi State University, Box 9681, Mississippi State, MS 39762-9681. S.H. Schoenholtz, Department of Forest Engineering, 267 Peavy Hall, Oregon State University, Corvallis, OR 97331-5706; P.D. Gerard, Department of Mathematics and Statistics, Mississippi State University, P.O. Drawer MA, Mailstop 9715, Mississippi State, MS 39762. Received 12 June 2005. *Corresponding author ([email protected]). Published in J. Environ. Qual. 35:837–848 (2006). Technical Reports: Waste Management doi:10.2134/jeq2005.0244 a ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA R e p ro d u c e d fr o m J o u rn a l o f E n v ir o n m e n ta l Q u a lit y . P u b lis h e d b y A S A , C S S A , a n d S S S A . A ll c o p y ri g h ts re s e rv e d . 837 Published online April 3, 2006