Cover crops promote soil health by encouraging vital fungi and retaining soil nutrients
"The more you use cover crops, the better your soil tilth, research continues to show. One reason is that cover crops, especially legumes, encourage populations of beneficial fungi and other microorganisms that help bind soil aggregates...
"By having their own mycorrhizal fungi and by promoting mycorrhizal relationships in subsequent crops, cover crops therefore can play a key role in improving soil tilth. The overall increase in glomalin production also could help explain why cover crops can improve water infiltration into soil and enhance storage of water and soil nutrients, even when there has been no detectable increase in the amount of soil organic matter...
"Cover crops help bring other nutrients back into the upper soil profile from deep soil layers. Calcium and potassium are two macronutrients with a tendency to travel with water, though not generally on the express route with N. These nutrients can be brought up from deeper soil layers by any deep-rooted cover crop. The nutrients are then released back into the active organic matter when the cover crop dies and decomposes."
Source: Marianne Sarrantonio, “Building Soil Fertility: Building Soil Fertility and Tilth with Cover Crops,” in Managing Cover Crops Profitably, 3rd ed., Sustainable Agriculture and Research Education, 2012, 18–19, accessed May 13, 2014, http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitabl....