Dry sieving, wet sieving, and soil analytical techniques were used to study the levels of organization within dry aggregates of virgin and cultivated krasnozem soils. Three mechanisms of aggregation appeared to exist. In the c 0.5 mm size range, the mechanism was independent of cultivation and was connected with basic soil particle properties. In the 5.0-0.5 mm range the hydrophobic properties of organic matter are proposed as important in determining water stability. In the range > 5.0 mm, binding of roots in the virgin soil and clod formation by implements in the cultivated soils appeared to be operative. Reduction in clay crystal size and surface activity appeared to be connected with phosphate fertilizer application.