If you've been given the pitch, and it's not called hype, because it appears to be true, about what cover crops in conjunction with conservation tillage or no-till can do to improve soil health on your farm, then you're probably a candidate to purchase a copy of 'Midwest Cover Crops Field Guide.' It's a brand new publication that is 137 pages about nothing but cover crops. You can learn more at: www.mccc.msu.edu, or you can learn how to buy one or more copies by visiting the Purdue University Education Store for university material. Visit: www.the-education-store.com or call 888-EXT-INFO.
Let's say you're interested in cover crops because you want to get more nitrogen for your corn crop. On page 87 you'll see a simple chart that shows hairy vetch has the highest rating possible as an N source. When allowed to grow in the spring, this legume is an N- making machine. However, if you want to scavenge up N during the fall that might be left behind by the previous crop, hairy vetch isn't your choice. It only rates one dot out of 4 when it comes to being an N scavenger. Its' strength is making N, not pulling it out of the soil and saving it.
Contrast that to cereal rye, planted in the fall for winter cover. This grass and most other grasses strike out, with zero green dots, as an N producer. However, rye rates as a 4-star N scavenger- top of the line. Once the rye is killed in the spring, and decomposition is allowed to take place, that N will eventually be available to the new crop growing in the field. The tough part is making sure the young corn crop has enough N to keep it going between the time the rye is killed and the time it begins to break down and release N for use by another crop.
Annual ryegrass, popular for its deep rooting, rates the same as rye on the nitrogen scale. It's not a producer, but it is a very good scavenger of N left behind in the field in the fall. By tying up the N, these plants help reduce the flow of nitrate out of the field either in streams or in underground tile lines.