The dispersion of clay in soil can lead to a number of agricultural and environmental problems. The purpose of the experiments reported here was to investigate the effects of soil organic matter content on the dispersibility of clay. Soil samples were collected from a longterm field experiment on a sandy soil (4% clay) in which different crop rotations and different fertilization practices had led to a range of soil organic matter contents. Clay dispersibility was measured with a turbidimetric technique. This showed clearly that increasing contents of organic matter in the soil result in reductions in clay dispersibility.