Development of pedotransfer functions to quantify phosphorus saturation of agricultural soils

Soil P saturation affects the risk of P loss to surface and ground water and is therefore a critical environmental indicator in regions where eutrophication is a concern. In the USA, most soil testing laboratories do not include environmental indicators such as son P saturation as standard soil test options. Development of pedotransfer functions that relate soil test data to soil P saturation, however, would enable soil testing laboratories to estimate soil P saturation as part of soil test results without significant additional expenditures. This study examines associations between readily-available soil test data (pH, soil organic matter, and extractable P, Al, Fe, and Ca) and soil P saturation as estimated by add ammonium oxalate extraction. Fifty-nine soil samples were collected from the Delaware River Watershed in New York State (42 degrees 21'N, 74 degrees 52'W) and subjected to standard soil test analyses as well as to acid ammonium oxalate extraction. Some soil test variables were well correlated with soil P saturation. As a single predictor, soil test P was most highly correlated to soil P saturation (r = 0.88). This association supports the use of soil test P as an environmental indicator. Soil test Al also was well: correlated with soil P saturation following logarithmic transformation (r = 0.73). Multivariate pedotransfer functions containing soil test P, Al, Fe, soil organic matter, and pH did not significantly improve estimation of soil P saturation (R = 0.91) above soil test P alone.