In a 7-year study of eight summerfallow treatments, the percentage of erodible soil (soil particles < 0.84 mm in diameter) at the completion of tillage in the fall, and prior to preseeding tillage the following spring, was significantly influenced by the summerfallow method. The Wood Mountain clay loam soil studied was significantly less erodible in the spring than it was the previous fall, indicating overwinter aggregation of the erodible fraction.