Mobility of Poultry Litter Phosphorus in a Coastal Plain Forest Soil

Abstract

Loss of phosphorus (P) to surface waters from forest soils fertilized with P-rich poultry litter (PL) is likely less than P loss from pasture because forest soils are typically lower in P. This study examined P mobility where PL was applied to forest soil in amounts constituting disposal. Triplicate plots (13.4 × 3.1 m) of 4-year-old loblolly pine (Pinus taeda) were amended once per year at 0, 5, 10, and 20 Mg PL/ha in 1996 and 1997–2001. Surface soil (0–15 cm) P was monitored annually during the application period and at varying frequencies until 2013. Cores to 1 m were taken in 2002 and 2013. Phosphate sorption in surface and subsoil was measured, and transport in surface soil was investigated. Sorption after 24 h followed the Langmuir model, which described retention during transport better than a linear model but not as well as a two-site kinetic Langmuir model with sorption capacity based on oxalate-extractable aluminum (Al) + iron (Fe). Phosphate sorption was least in 15- to 30-cm depth soil; sorption increased deeper into the Bt horizon. Neither the increase nor the decrease in surface soil P showed a clear effect of sorption nonlinearity. Treatment effects were significant to a depth of 45 cm in 2002 except for organic P (surface only). The profile distribution of P was generally consistent with sorption, with some evidence of preferential flow. Leaching from 2002 to 2013 was slow, moving P in 20-Mg ha plots to 60 cm. However, leaching was likely increased by initial concentrations and fast relative to tree uptake.