Fighting Plants with Plants
Controlling weeds, especially in this era of herbicide resistance, is a multi-stage process. Farmers can’t just rely on a quick application of herbicide, and we now better understand how heavy tillage burns up soil organic matter and loses tons of topsoil every year to erosion. Fortunately, one practice that is becoming recognized as an integrated weed management tool is also a highly effective soil builder: planting cover crops.
What surprises many farmers is how effective a good cover crop stand can be in controlling weeds. Research at the University of Illinois demonstrated that a uniform cover crop of cereal rye (seeded at 40 pounds per acre) before soybeans can provide 98% control of marestail, also known as horseweed. That’s an impressive figure, especially in light of the fact that many populations of marestail have become resistant to popular herbicides.
How do cover crops fight weeds?
Cover crops fight weeds several ways. First, established cover crops take up space and sunlight needed by germinating weeds. That’s why they are especially effective against winter annuals like marestail. Many cover crops, including cereal rye, also exude chemicals that inhibit the germination or growth of competing grasses—an effect called allelopathy.
The process of terminating a winter-hardy cover crop, whether with herbicides or a roller, can also contribute to your weed control efforts. The cover crop residue left on the surface can serve as a mulch that shades out weeds that would emerge in the spring.
Meanwhile, the cover crop is doing much more than suppressing weeds. Its roots are capturing nutrients in the soil that might otherwise leach out of the root zone and maybe into tile lines or groundwater. Those nutrients are turned into biomass that decays after the cover crop is terminated, which returns the captured nutrients to the upper inches of soil, builds organic matter and sustains the cash crop to follow.
Cover crop roots—fibrous networks like those of cereal rye or massive taproots like a turnip or radish—also provide natural “tillage” for the soil, loosening compacted layers and clearing paths for cash crop root systems. Legume cover crops even fix atmospheric nitrogen in the soil.
Farmers need to take an integrated approach to managing weeds
Cover crops are a great example of the systems approach to farming … and weed management … and conservation. They’re a vital component of the fundamentals of conservation farming systems, which should also include:
- conservation tillage
- no-till or strip-till
- crop nutrient management like the 4Rs of Nutrient Stewardship
- good weed and pest management and
- conservation buffers.
Another great benefit of cover crops is that they are often eligible for federal, state or local funding and free technical advice from CTIC, your local conservation district or Natural Resources Conservation Service office. That means they can help draw money into your farm while building up its value by restoring depleted soil organic matter, providing the public service of cleaner water, reducing weed pressure, and enhancing your operation for the next generation.
Cover crops are more than just a great conservation measure—they are a valuable part of an integrated weed management system, and a tool that leads to greater efficiency, productivity and profitability.