Cover crop mixtures may be the way of the future! I’ve coined them the silver buckshot of cover cropping because silver bullets are hard to find.
Some knowledge of cover crop mixtures has been around for decades, if not centuries. In 1918, USDA produced a bulletin to help farmers increase yields by using cover crops and maintaining organic matter. In it, growing mixtures of grasses and legumes was recommended because the combination performed better than the individual components in monoculture.
Nearly a hundred years later, we are experiencing a resurgence of interest in and dedication to using cover crops for soil quality and farm profitability. Ongoing research (see this eOrganic factsheet from Penn State) continues to investigate the interactions of grasses, legumes, and now brassicas grown in combination with one another.
Farmers are planting “cocktails” of up to 15 or 20 cover crop species, but you can get a benefit from using just two or three species.
How to go about planning mixtures
It’s important to tailor any mixture to your specific goals and farm. Charlie White wrote a nice summary of this process. Mixtures can mitigate risk through diversity.
One approach to cover crop mixtures is to precision plant specific cover crops to fill a certain niche. For example, rows of radish can be planted at the spacing of the subsequent corn crop to provide a sort of “strip” tillage zone while oats in between the rows provide more soil cover for moisture conservation. This strategy can also be used as a type of nutrient banding when the radishes decompose in spring.
Guihua Chen and Cerruti Hooks at the University of Maryland have also used a forage radish and red clover mixture prior to corn planting. Including a legume such as red clover in a mixture may be beneficial in N-deficient soils. Read more about their results here.