Tuesday, November 14, 2006 - 10:30 AM

Phosphorus Forms and Concentrations in Soil and Ground Water Among Cropland-Riparian Areas.

Eric Young, Univ of Vermont, Dept of Plant & Soil Science, Hills Agricultural Bldg, 105 Carrigan Drive, Burlington, VT 05405 and Russell Briggs, SUNY College of Environmental Science and Forestry, 1 Forestry Dr, Syracuse, NY 13210.

Phosphorus (P) loss from agricultural soils to surface and subsurface runoff is a concern where high P availability and transport potential coexist. We characterized forms and concentrations of P for sixteen paired cropland-riparian plots over 2004 and 2005 to examine factors affecting P mobility in soils and ground water. Sodium acetate extractable P (NaOAc-P) and soil P sorption saturation (Psat) were determined on composite plot samples (0 – 30 cm). Soil solution (25 and 50 cm) and shallow ground water dissolved (<0.45μm) reactive P (DRP) were monitored in 2004-2005. Ground water particulate (>0.45 μm) reactive P (PRP) and dissolved unreactive P (DUP) were measured in 2005. Results showed that mean soil solution DRP in corn plots (70 - 215 μg L-1) was significantly greater than hay fields and buffers (<2 -77 μg L-1). Differences in soil solution DRP with depth were only significant where NaOAc-P was higher. Soil Psat was highly correlated with NaOAc-P among plots and highly correlated with soil solution DRP. Mean ground water DRP in cropland was generally ≤20 μg L-1 in 2004, but increased in 2005 (26 - 80 μg L-1). Ground water DRP in buffers remained low (<15 μg L-1) both seasons. Soil organic matter (OM) and 50 cm DRP jointly explained 75% of riparian ground water DRP variability. An average of 39% to 71% of ground water RP was PRP, and 38 to 92% of dissolved P was DUP in 2005. Forest buffer (hydric soils) ground water had the highest mean PRP (50 μg L-1), DUP (136 μg L-1) and total dissolved P (143 μg L-1). Results show that soil P status and soil-landscape (e.g. soil series, drainage class, OM, redox status, and hydrology) characteristics strongly influenced subsurface P forms, concentrations and mobility in cropland-riparian areas.