Isothermal Titration Calorimetry for Estimating Phosphorus Adsorption and Desorption Potential from Soils.

Removal of nutrients by sorption is an important process in regard to soil fertility and environmental quality.  More specifically, the energetics or strength of sorption will have a significant impact on nutrient and contaminant availability and mobility.  One method of direct measurement of sorption energy is isothermal titration calorimetery (ITC).  The objective of this study was to examine the ability of ITC to indicate phosphorus (P) sorption capacity and strength onto 28 different Oklahoma soils.  Soils were characterized by a P adsorption isotherm with subsequent fitting to the Langmuir adsorption model, ammonium oxalate degree of P saturation (P/[Al+Fe]), water soluble P, particle size analysis, and a single point P isotherm followed by a sequential desorption isotherm using de-ionized water.  Results indicated that the heat of P titration determined by ITC was well related to P sorption strength and P sorption capacity.  This suggests that ITC can serve as a simple and fast tool for comparing P adsorption and desorption potential between different soils.