Biswanath Dari1, Vimala D. Nair2, Dean Rhue1 and Mylavarapu Rao1, (1)University of Florida, Gainesville, FL (2)Soil and Water Science Department, University of Florida, Gainesville, FL
Determination of Langmuir isotherms and subsequent calculation of k, the phosphorus (P) bonding strength, and the equilibrium P concentration (EPC0) of a soil is a tedious and time-consuming process. We hypothesized that k and EPC0 should be related to the P saturation ratio (PSR) as determined by P, Fe and Al concentrations in an oxalate or a soil test solution such as Mehlich 1 or Mehlich 3. Langmuir adsorption isotherms were constructed for 52 soil samples collected from the Lake Okeechobee Basin and k and EPC0 values were computed. The soils were also analyzed for P, Fe and Al in an oxalate solution and PSR calculated as the molar ratio of P to Fe and Al. The threshold PSR value for these soils is 0.05 with a 95% confidence interval from 0 to 0.1. Results indicate that the k value is high below the threshold PSR and that the value tends to zero after the threshold value. EPC0 values are minimal below the threshold PSR and increases linearly after the threshold. Therefore it should be possible to obtain EPC0 and k values at minimal costs by submitting a soil sample to a soil testing laboratory. A simple procedure for determining k would be valuable when such values are needed as input in models for predicting P release from soils.