Pioneering cover crop use in the 1990s, University of Illinois Extension educator Mike Plumer discovered something that surprised everybody. Annual ryegrass has a root structure that grows to depths of more than five feet over winter, while the top growth is pretty much dormant.
One of annual ryegrass’ most compelling features is that deep rooting system, because it breaks up compaction of all kinds, and in doing so, it also helps bring nutrients deeper in the soil profile up to the surface. This not only helps crops thrive, it also reduces the amount of nutrient inputs needed.
So, it’s unclear why Cornell and Michigan State universities still have printed information about annual ryegrass stating that annual ryegrass has “a shallow” rooting system.
In fact, the plant DOES have a shallow root mass, which makes it valuable for preventing erosion. But what they don’t say is that annual ryegrass roots also grow to depths of five feet. And this is equally important, for reasons stated above.
In sum, the combined root mass of annual ryegrass also provide another benefit: helping to build organic matter in depleted soils. Once the plant is terminated, in springtime just before planting corn or soybeans, all that root matter decays and becomes the basis for a healthy population of microorganisms and a more friable soil.
(In the photo above, growers are inspecting deep channels created by annual ryegrass roots, which allow corn roots more penetration into the soil following those same channels. Thus, corn plants can better tolerate dry weather because they can reach deeper into soil for needed moisture.)
Plumer said that because of long-term tillage practices, plus tiling fields for drainage and not planting cover crops, Midwest soils have lost half or more of their organic matter. The good news is that for every additional percentage point of organic matter you can add back into the soil, you’re adding back about 1000 pounds of nitrogen per acre!
Annual ryegrass and other cover crops help to raise the organic level back up, though it takes years of consistent cover crop use to make up for the decades of less productive management methods including heavy tillage.