Location: Agroecosystems Management ResearchTitle: Mobility of poultry litter phosphorus in a Coastal Plain forest soil
|WIGHT, JASON - Louisiana State University|
|WALDRON, GREGORY - Louisiana State University|
|GATSON, LEWIS - Louisiana State University|
|BLAZIER, MICHAEL - Louisiana State University|
Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2015
Publication Date: 10/28/2015
Citation: Wight, J.P., Waldron, G.J., Gatson, L.A., Blazier, M.A., Kovar, J.L. 2015. Mobility of poultry litter phosphorus in a Coastal Plain forest soil. Soil Science. 180(3):124-133.
Interpretive Summary: Poultry production is the largest agricultural animal industry in Louisiana, so it is vital to the state’s economy. Research has shown that application of poultry litter for many years has led to a build-up of soil phosphorus (P) in some areas of north Louisiana. This P can negatively impact water quality in nearby lakes and streams. With a field study in a loblolly pine tree forest, we evaluated the potential movement of P during a 12-year period (2001-2013) following six annual applications of four rates (0, 5, 10 and 20 Mg ha-1) of poultry litter to a Louisiana Coastal Plain soil common to the area. We monitored available P in the surface soil and estimated soil P saturation in both the surface soil and subsoil to a depth of one meter. Phosphorus leaching was fast compared with uptake by loblolly pine, so that a substantial fraction of any applied P may not be retained in tree biomass. However, the high initial concentration of P in soil at this site (140 mg kg-1 Bray 2P) presumably reduced further P retention by the soil and increased leaching. Since conversion of fertilized pasture to timberland is common in the coastal plain of Louisiana and elsewhere, results of the field study are broadly relevant. Given the current emphasis on non-point source losses of P, this information will assist producers in managing and utilizing the nutrients in poultry litter.
Technical Abstract: Loss of phosphorus (P) from soils may eutrophy surface waters. Use of P-rich poultry litter (PL) for fertilization of forest soils is an environmentally beneficial alternative to use for pasture fertilization because forest soils are typically low in P compared to pasture soils. This study examined P mobility where PL was applied to a forest soil in amounts constituting disposal. Triplicate plots (13.4 x 3.1 m) of four year-old loblolly pine (Pinus taeda) were amended at 0, 5, 10 and 20 Mg PL ha-1 annually six times from 1995 to 2001. Surface soil (0–15 cm) P was monitored from 1995 to 2013. Cores to 1 m were taken from plots in 2002 and 2013. Sorption and transport of phosphate in surface soil were investigated in batch and column studies. Sorption after 24 h followed the Langmuir model, which approximately described sorption/desorption during transport. However, a two-site, kinetic Langmuir model with sorption capacity based on oxalate-extractable aluminum (Al) + iron (Fe) better described movement. Sorption exhibited low affinity and fast kinetics (rate coefficients ~ 1 d-1). Build-up of P in surface soil during years of fertilization may have decreased as the sorption maximum was approached. Treatment effects were significant to a depth of 45 cm in 2002 except for organic P (surface only). Leaching during the next 11 years was slow, moving P in 20 Mg ha-1 treatment plots to 60 cm. However, leaching was likely increased due to initial soil P, and fast relative to tree uptake.