There are actually 2 different cover crops interplanted on this field, rye and Austrian winter peas. The rye is a cereal grain that is suppose to secrete a substance that inhibits the growth of certain weeds and can also help in nematode control. The Austrian winter peas are "legumes" whose roots contain nitrogen-fixing bacteria that add nitrogen to the soil.
Here is a close-up picture where you can see both types of plants. There is some henbit in there, too. Just forget that is there. Obviously, THAT is not one of the winter weeds that rye is suppose to kill!