Assessing the phosphorus sorption capacity of Mollisol soils using the Langmuir isotherm and single-point sorption index techniques

CHED 1096

Aleela Baune, buresha@southwestmsu.edu and Frank V. Schindler, schindlerfr@southwestMSU.edu. Department of Chemistry, Southwest Minnesota State University, 1501 State Street, Marshall, MN 56258
Phosphorus (P) adsorption by soils is an important parameter for determining the environmental fate of P. While P sorption isotherms are useful for the characterization of the P sorption capacity of soils, traditional P sorption isotherms are too time-consuming and expensive for routine use. A single point P sorption index (PSI) may be an effective alternative to the traditional isotherms for determining the P sorption capacity of soil. In order for the PSI method to become widely adopted as a routine test of a soil's P retention capacity, it must be evaluated over a wider range of soils. This study correlated the P sorption maxima as determined by the traditional Langmuir equation to the PSI method. 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 correlations between the Langmuir P sorption maxima and PSI are presented.