The present study was carried out in Kharkeh Research Station, Kurdestan Province, western Iran to investigate the effects of the change in land use on the degradation of Mollisols, their organic carbon content, clay mineralogy and K+ status. The study area was partly under cultivation (for over 40 years) and partly preserved as rangelands. The results revealed that Mollisols are the dominant soils in non-cultivated natural rangelands. The adjacent cultivated soils, however, lack enough organic carbon to meet the requirements of Mollisols. Cultivation practices had exerted adverse effects on some such major soil properties as organic carbon, cation exchange capacity, as well as macro- and microstructure. Clay minerals and different forms of potassium did not show significant differences in the two land uses. Parent material rich in such potassium bearing minerals as feldspars and mica, as well as the dominance of illite in soils, were probably the main factors responsible for adjustment of the soil K+, rendering the changes relatively nonsignificant.
