Establishing cover crops remains the biggest challenge facing producers who currently use cover crops and is the second biggest barrier to cover crop adoption for non-users (2014-2015 Cover Crop Survey- CTIC & NC-SARE); below is the latest information from around the Midwest.
Managing Cover Crop Profitably (SARE Handbook Series Book 9) by Andy Clark (2007, 3rd ed.) is a good resource for getting started with cover crops.