Assessing the Langmuir and single-point phosphorus sorption maxima of select mollisol soils

CHED 1067

Angela Gunlogson, gunloga@southwestMSU.edu and Frank V. Schindler, schindlerfr@southwestMSU.edu. Department of Chemistry, Southwest Minnesota State University, 1501 State Street, Marshall, MN 56258
A single point phosphorus (P) sorption index (PSI) may be an effective alternative to the traditional Langmuir isotherm for determining the P sorption capacity of soil. Previous research indicates a positive correlation between the P sorption maxima as determined by the Langmuir isotherm and the PSI. This study continues to evaluate the efficacy of the PSI in determining the P sorption capacity of soil. Separate air-dry soil samples of select mollisols were subjected to: 1) a series of equilibrating solutions ranging in their P concentrations, and 2) a single solution of known P concentration. The P sorption maxima were determined by modeling the data to the linearized form of the Langmuir equation. The amount of variability in the Langmuir sorption maxima explained by the PSI method is presented. This study provides additional information regarding the use the PSI method as a routine test of a soil's P retention capacity.