an assessment of the dynamics of physical fractions of organic carbon in water-stable aggregates within different types of land uses

throughout the present study, similar horizons (a, ab and b1) from deciduous forest, coniferous forest and rangeland types of land uses were selected, and the percentage of water stable aggregates in them measured. in each class of stable aggregate at the horizon a, free light fraction, free-particulate organic matter, intra-aggregate of particle organic mather (pom), and clay + silt complexes were separated through density and size method. carbon and nitrogen percentages were measured by use of chn elemental analyzer. results of the study indicate that along with decrease in aggregate size, stable aggregate as well as organic carbon percentages were increased. it was also found that large macro aggregates (>2 mm) were more susceptible to the change to deciduous forest-land than the other aggregates. based on organic matter fractionation techniques, free particulate organic matter and intra-aggregate particulate organic matter among other fractions, and even total organic carbon are critical and sensitive indicators of change into other types of land uses. the levels of nitrogen and c: n of organic matter fractionation were determined within the degradation order of f-lf> f-pom> ia-pom> ia-s+c, which revealed the main role of aggregates in conservation of organic matter.