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Abstract: Phosphate adsorption on soils in the Gurghiu and Harghita Mts., Romania. Ten soil profiles from the Mezőhavas region of the Gurghiu Mountains and ten from the Vf. Madarasi Tető region of the Harghita Mountains were investigated by taking samples from the various horizons of each profile, leading to a series of 39 soil samples from Gurghiu and 37 from Harghita. In the course of the work the rate of phosphate adsorption on the soils was determined, and correlations were sought between chemical soil properties and the rate of adsorption. The maximum adsorption rate was calculated with the help of the Langmuir isotherm, and numerous other soil properties were examined in order to determine which parameters were correlated with the rate of phosphate adsorption. Among the soil properties, the oxalate-soluble Al and Fe contents, i.e. the non-crystalline Al and Fe oxyhydroxides, proved to be in close, positive, approximately linear correlation with the phosphate adsorption rate for both groups of soils. In addition, phosphate adsorption exhibited a close, negative, exponential correlation with the quantity of exchangeable cations, and a positive linear correlation with the pyrophosphate-soluble Al, i.e. that bound to organic matter.

Keyword: Soil profiles, Gurghiu Mts., Harghita Mts., Phosphate adsorption, Exchangeable cations, Organic matter, Langmuir isotherms