Identifying Soil Phosphorus Sources and Sinks within Land-Use Systems of the Lake Okeechobee Basin.

Phosphorus loading of Lake Okeechobee has lead to accelerated eutrophication.  Identifying soils in the watershed as P sources or sinks is critical for implementing best management practices (BMPs) to reduce P loss from soils.  P releases from soils are dependant on soil properties and land-uses.  Phosphorus saturation ratio (PSR) and soil P storage capacity (SPSC) of 62 soils across 15 different land uses and 7 soil orders (0-20 and 20-40 cm depths) in the Okeechobee watershed were determined.  Soils were analyzed for water soluble phosphorus (WSP) and Mehlich 1(M1)- P, Fe, and Al.  The WSP for land-uses ranged from 0 to 108 mg kg^-1 with highest levels in some improved pastures, citrus groves and dairy locations.  The P saturation ratio (M1-P/(M1-Fe + M1-Al)) ranged from 0 to 74, and 27 of the soils have the potential to release P based on the previously identified PSR threshold of 0.1.  These soils included all land uses sampled except for coniferous forests, cypress and ornamentals.  Soils with a PSR>0.1 have a negative SPSC, ((0.1-PSR_soil)*(M1-Al + M1-Fe)*31(mg/kg)*1.93) and must implement BMPs to reduce their environmental impact as a P source.