Phosphate Sorption Characteristics of European Alpine Soils

We evaluated the chemical properties controlling phosphate (PO 4 –P) sorption characteristics of alpine soils at elevations of 1725 to 2900 m above sea level in four European mountain ranges (the Tatra Mountains, Slovakia and Poland; the Alps, Austria; the Pyrenees, Spain and France; and the Rila Mountains, Bulgaria). PO 4 –P sorption isotherms were determined, ranging in concentration from 0 to 6.5 m M KH 2 PO 4 at original soil pH, and were evaluated using the Langmuir equation. PO 4 –P sorption maxima (X max ) varied from 6 to 145 mmol kg −1 in the dry (105°C) fine soil fraction (<2 mm). Concentrations of Al oxohydroxides, determined as oxalate extractable aluminum (Al o ), ranged between 36 and 770 mmol kg −1 , and were the dominant parameter affecting the soil's ability to adsorb PO 4 –P. In the Tatra Mountains, Rila, and Alps, oxalate‐extractable iron (Fe o ) was also important, while in the Pyrenees we found a significant correlation ( p < 0.01) between X max and total organic C concentrations. The ability of Al and Fe oxohydroxides to adsorb PO 4 –P was higher in areas with more acidic soils (the Tatra Mountains) than in areas with higher soil pH (the Pyrenees), and in the more acidic uppermost organic soil horizons than in mineral soil horizons. A simple model based only on two basic soil characteristics (Al o and pH) explained 81 to 89% of the X max variability observed in individual mountain areas and 74% of the X max variability associated with all samples.