From BobVila.com….
Throughout the growing season, garden plants work together with microbes to break down and use organic matter within the soil. During the off season, unprotected garden beds are at risk of erosion, a process that strips away the topsoil resulting in a loss of nutrients, and soil compaction, which reduces water infiltration and drainage, damaging the soil structure. Over time, this seasonal cycle can leave your garden infertile and unproductive. But this problem is easy to avoid by adopting a few soil friendly habits in the fall.
When the growing season comes to an end, the soil building season begins. This is the time to focus on rebuilding organic content, conserving nutrients, preventing erosion, and avoiding soil compaction.