Tuesday, November 14, 2006

Phosphorus Sorption and Soil Variability in Louisiana Coastal Plain Soils.

Gregory J. Waldron1, Lewis Gaston2, Darren Cooper3, and Matt Stephens1. (1) Lousiana State Univ, AgCenter, Dept of Agronomy and Env Mgmt, 104 Sturgis Hall, Baton Rouge, LA 70803, (2) Lousiana State Univ, Agronomy & Env. Mgmt., 104 Sturgis Hall, Baton Rouge, LA 70803-2110, (3) Louisiana State Univ., AgCenter, Calhoun Research Station, Calhoun, LA 71225



Soil phosphorus (P) build-up from long-term application of poultry litter may increase P loss in surface and subsurface water and lead to eutrophication.  Pasture sites in North Louisiana were surveyed for elevation and grid sampled on 60 x 60, 30 x 30 and 15 x 15 m scales.  The soils included Darley (fine, kaolinitic, thermic Typic Hapludult) and Ruston (fine-loamy, siliceous, thermic Typic Paleudult) series.  Core samples of surface 0 – 5 cm, 5 cm – Bt and the first 5 cm of Bt were analyzed for P content, pH, organic C, oxalate-extractable Al and Fe, and texture.  Phosphorus sorption isotherms were also generated, fit to the Langmuir isotherm, and the data were geostatistically analyzed.  Isotherm parameters were spatially correlated and well-described by exponential and Gaussian semivariograms.  Among soil properties, P sorption parameters were best correlated with oxalate-extractable Al and Fe.   This study was part of a larger project where the goal is to refine a set of criteria that will allow an applicator to determine the amount of P that a specific location in a particular soil can retain without appreciable loss to surface waters.