Cover crops/OM have their benefits, but no free lunch with them either.  We had to replant over 60 acres of beans this spring that were planted into heavy barley cover, resulting in slug pressure.

The pictured field had barley harvested for forage before planting corn.  This is common practice for many here in the valley, even those without irrigation, and it usually works out.  Lots of dairy and poultry manure is used around here also.