Soil management systems have greater effect on soil chemical, physical and biological properties. Conversion of
forest to grassland and cultivated land can alter carbon and nitrogen dynamics. The objective of this study was
to evaluate the changes in biological and physical carbon and nitrogen fractions after conversion of native forest
to grassland and cultivated land in the northern Turkey. Some soil physical, chemical, and biological properties
were measured. Soil texture ranged from sandy clay loam through clay loam. The highest bulk density was
observed in the grassland (1.41 g cm-3) and the lowest one was in the cultivated land (1.14 g cm-3). Soil pH was
the similar (pH = 7) in the three land uses. Microbial biomass C and total organic carbon were almost two times
greater in the forest than forest cleared grassland and four times greater than cultivated land. The greater portion
of organic carbon was stored in macro aggregates (>250 micron) in the three land uses. Physically unprotected
organic carbon (light fraction) comprises smaller portion of soil organic carbon in the three land uses. Therefore,
this study indicated that microbial biomass C, mineralizable C, and protected organic C decrease in forest
cleared grassland and cultivated lands
