The Sustainable Agriculture Network (Maryland) has this to say about annual ryegrass. (See below, in italics.)
If you want to build soil without investing much in a cover crop, consider annual ryegrass. A quick-growing, non-spreading bunch grass, annual ryegrass is a reliable, versatile performer almost anywhere, assuming adequate moisture and fertility.
It does a fine job of holding soil, taking up excess N and outcompeting weeds. Ryegrass is an excellent choice for building soil structure in orchards, vineyards and other cropland to enhance water infiltration, water-holding capacity or irrigation efficiency.
It can reduce soil splash on solanaceous crops and small fruit crops, decreasing disease and increasing forage quality. You also can overseed ryegrass readily into corn, soybeans and many high-value crops.
While you’re looking at cover crop choices, you should also check out the Midwest Cover Crop Council’s site. It’s a great resource of information on various cover crops, and features a handy matrix for determining the best cover crops to use, based on your location, soil quality and cash crops used in rotation.