Sociedade & Natureza, Uberlândia, Special Issue, 440-445, May, 2005 440 VARIATIONS IN SOIL PROPERTIES AS AFFECTED BY DEFORESTATION ON LOESS-DERIVED HILLSLOPES OF GOLESTAN PROVINCE, NORTHERN IRAN Farhad Khormali * Reza Ghorbani Rahim Amoozadeh Omrani Dept. of Soil Science, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran * Khormali@ gau.ac.ir ABSTRACT Deforestation and shift of land use to agriculture, is of great concern in Golestan Province and has brought hazardous problems of flooding, landslide and soil loss. Soil organic carbon, total nitrogen content, available phosphorous and potassium, calcium carbonate content, thickness of A horizons and some important soil properties were studied on forested soils and compared with the adjacent deforested and cultivated soils. The studied soils were formed on a hillslope with parent material consisted mainly of loess deposits. Forested and deforested soils were classified as Calcic Hapludolls and Typic Hapludolls, respectively. The studied soils were all calcareous with the pH value of 7-7.9. The soil texture was silty clay loam with the silt content of 54-60%. The results revealed that the soil organic carbon, total nitrogen content and available potassium, were significantly lower in the deforestated soils. The thickness of mollic horizons was also reduced after deforestation in all studied pedons. While calcium carbonate contents of the subsurface horizon of the forested soils are significantly higher compared to the surface horizon due to the leaching processes, it is considerably high in the surface horizons of the deforested soils and does not change significantly with depth. This points to the effect of deforestation and cultivation practices which has led to soil erosion and the subsequent exposure of the highly calcareous subsurface horizon. Available soil phosphorous did not show any significant change by deforestation. Keywords: Deforestation, land use change, loess, Iran INTRODUCTION Increase in population and a continuous decline in the amount of agricultural land have led to an indiscriminate exploitation of natural forests and fragile lands for agriculture (Mahtab and Karim, 1992). Soil organic matter and soil nutrient depletion are among the major forms of