Cover Crop Root Growth – Annual Ryegrass

Steve Berger did a trial of annual ryegrass this past winter. It was ideal soil, having been in no-till for 25 years. On one plot he planted cereal rye; on the other he compared the growth of four annual ryegrass varieties.

Iowa has lagged behind other Midwest states in adoption of cover crops. Berger’s farm, in SE Iowa, is an ideal place to test it out. In that respect, Berger is an early adopter for trying annual ryegrass.

The winter was unusually mild and, thus, all the annual ryegrass did well, as did the cereal rye (a grain, not a grass). The surprising thing, when he did a root depth analysis…the cereal rye roots went deeper into the soil than annual ryegrass. Usually, on poorer soils, the opposite it true: annual ryegrass roots sometimes go as deep as 60 inches over the winter, while cereal rye roots are much shallower.

Two theories. One, annual ryegrass roots seek nutrients and moisture. On the Berger farm, there was plenty of nutrients and moisture in the no-till soil, thus they didn’t need to work overtime to get nutrition. Secondly, he did the tests in early April, a couple weeks earlier than usual. Perhaps a couple more weeks of root growth would have added more root depth.

Another thing to consider in the next year…whether cover crops tend to do better after corn or soybeans. Corn is more demanding of nitrogen, and thus the amount of available nitrogen in the soil might impact the growth of a following cover crop, especially if nitrogen was not added.


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