PHOSPHORUS SOIL TEST CORRELATION TO SUGARCANE GROWN ON HISTOSOLS IN THE EVERGLADES

Sugarcane (Saccharum spp.) in Florida is principally grown on Histosol s in the Everglades Agricultural Area. Soil-test-based P fertilization recommendations have not been addressed since the 1970s. The objectiv es of this research were to evaluate the most acceptable soil test P e xtractant that best correlates to crop yield, and to define soil test P groupings associated with crop response to applied P. Results will b e used in the future to recalibrate soil test data to yield and rate o f P application. Phosphorus trials were conducted at four sites on org anic soils between 1968 and 1972 and additionally at eight sites on or ganic soils between 1982 and 1990. Phosphorus applications ranging fro m 0 to 98 kg P ha(-1) were broadcast or row-applied in combination wit h different cultivars, and/or K, Si, or S rates at 12 sites (multiple experiments used per site per crop). The effectiveness of water, aceti c acid, and Mehlich-1 extractable soil P as yield response predictors was determined. Acetic acid extractable P was more highly correlated t o sugar and cane yields (r = 0.72 and 0.63**, respectively) than wate r-extractable P (r = 0.27* and 0.39**, respectively). Mehlich-1 extra ctable P was poorly correlated to sugar (r = 0.25) and cane (r = 0.05 (ns)) yields. Acetic acid extractable P was selected as the best-suite d extractant related to crop yield response to P fertilization. Soil t est calibration curves (i.e., relative yield as a function of acetic a cid extractable P) were determined from the choice of seven types of r egression models, in which the reciprocal function was chosen with the highest coefficient of determination (R(2)) and minimized residuals. Soil acetic acid extractable P criteria were developed to define soil test level groups associated with yield response conditions: low soil test levels ranged from 0 to 9 mg L(-1), medium from 9 to 39 mg L(-1), and high exceeded 39 mg P L(-1).