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Phosphorus and potassium adsorption –desorption was studied in 10 mM calcium chloride for samples of subsoil horizons of four soil series, Golshar,Khomaini Shahr, Sheahreza and Manoochehrabad. The soils were calcareous with low OC content. The results of P sorption reactions were compared with three different models , simple Langmuire , Ferundlich, and Two-surface Langmuire equations. The maximum P sorption capacity varied from 833 –1250 ug/g soil and binding energy from 0.04 – 0.296 ml/ug. Gohshar Seri had the maximum P sorption affinity and Khomaini shar the lowest. The best correlation was found with Ferundlich equation. All soils had low desorption capacity, however Sheareza had the highest and Golshar the lowest desorption capacity. Analyzing the data showed a high negative correlation coefficient(r = -88%)between P sorption and clay contents of soils. Also a high correlation coefficient (r = 63%)was found between P sorption and calcium carbonate contents of soils. The results of K sorption showed that Khomaini shar had the highest and Golshar the lowest sorption affinity. The maximum sorption capacity varied from 52.9 –588.2 ug/g soil. A high correlation coefficient(r = 97%) was found between Xm and soil clay contents. However a high negative correlation coefficient(r = -97%) was found between Xm and clacium carbonate contents of soils. Desorption of K followed a linear regression equation with r > 99% for two successive desorption. Key words: adsorption,desorption, Phosphorus, Potassium ,soil series, maximum sorption capacity.

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