Used for cover crops as a biological tool to reduce th effects of soil compaction.  The roots of all cover crops can penetrate compacted soils in fall to some extent.  Radishes are exceptional at breaking up shallow layers of compacted soil, sometimes earning them the nickname of "biodrills" or "tillage radish".  Radishes will die, decay and contribute to a nitrogen store for spring planting.   Decayed radishes leave a root channel so the soil dries and warms up quicker in the spring.