Yes, ash dieback can be spread by contaminated soil from a previously infected tree. The fungus that causes ash dieback, Hymenoscyphus fraxineus, produces fruiting bodies that release spores which can contaminate soil. The spores can remain viable in the soil for several years, and infect healthy ash trees that grow in that soil.
The disease can also be spread by other means such as wind, rain, and insects, but contaminated soil is a significant pathway for its transmission. Therefore, it is important to take precautions when handling soil from areas with known ash dieback infections to prevent further spread of the disease.