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TECHNICAL REPORTS

Plant and Environment Interactions

Nutrient Dynamics and Tree Growth of Silvopastoral Systems: Impact of Poultry Litter

^a Hill Farm Research Station, Louisiana State Univ. AgCenter, 11959 Hwy. 9, Homer, LA 71040
^b Dep. Agronomy & Environ. Management, Louisiana State Univ. AgCenter, 224 M.B. Sturgis Hall, Baton Rouge, LA 70803
^c USDA-NRCS, 3737 Gov. St., Alexandria, LA 71302
^d Arthur Temple College of Forestry & Ag., Stephen F. Austin State Univ., Box 6109 SFA Station, Nacogdoches, TX 75962. This manuscript was approved for publication by the Director of the Louisiana Agricultural Experiment Station as manuscript 07-54-0294

^* Corresponding author (mblazier{at}agcenter.lsu.edu).

Received for publication June 27, 2007. Fertilizing pastures with poultry litter has led to an increased incidence of nutrient-saturated soils, particularly on highly fertilized, well drained soils. Applying litter to silvopastures, in which loblolly pine (Pinus taeda L.) and bahiagrass (Paspalum notatum) production are integrated, may be an ecologically desirable alternative for upland soils of the southeastern USA. Integrating subterranean clover (Trifolium subterraneum) into silvopastures may enhance nutrient retention potential. This study evaluated soil nutrient dynamics, loblolly pine nutrient composition, and loblolly pine growth of an annually fertilized silvopasture on a well drained soil in response to fertilizer type, litter application rate, and subterranean clover. Three fertilizer treatments were applied annually for 4 yr: (i) 5 Mg litter ha^–1 (5LIT), (ii) 10 Mg litter ha^–1 (10LIT), and (iii) an inorganic N, P, K pasture blend (INO). Litter stimulated loblolly pine growth, and neither litter treatment produced soil test P concentrations above runoff potential threshold ranges. However, both litter treatments led to accumulation of several nutrients (notably P) in upper soil horizons relative to INO and unfertilized control treatments. The 10LIT treatment may have increased N and P leaching potential. Subterranean clover kept more P sequestered in the upper soil horizon and conferred some growth benefits to loblolly pine. Thus, although these silvopasture systems had a relatively high capacity for nutrient use and retention at this site, litter should be applied less frequently than in this study to reduce environmental risks.

Abbreviations: C, subterranean clover presence • ICP, inductively coupled plasma • INO, inorganic fertilizers • 5LIT, 5 Mg litter ha^–1 • 10LIT, 10 Mg litter ha^–1 • NC, absence of subterranean clover • NOF, no fertilization