The best offense is a great defense. Planted cover crops provide living roots to keep soil in place but they are also working by collecting nutrients. On the surface and beneath the soil there can often be an abundance of nutrients waiting to be used from previous fertilizer applications. These excess nutrients are often washed away or leached during winter rains. The best way to capture these is to have an actively growing plants that can use these as food. These crops will capture nutrients throughout the winter essentially holding them for later use. When choosing a cover crop look for a blend that includes a variety of plants to collect nutrients in different ways. Then in the spring when the cover is terminated the nutrients will be available again. The soil will have had food for the winter helping maintain its health and keep those inputs from getting away.
For more extensive information, check out this OSU publication. Remember that another benefit of a cover crop is protecting your soil from the compacting effect of heavy rain. Thing of a growing green umbrella….