Corn harvest is when many farmers are ready to drill cover crops into their fields. Cover crops offer an array of well-known benefits, including erosion control, weed suppression, increase in soil organic matter, increase in soil nitrogen (when using legumes) and possibly a source of livestock forage.

In some cases, such as after chopping for silage or in more southern areas of the Mid-Atlantic, it’s easier to establish a cover crop behind corn. In other cases – when it’s too wet to get in and combine corn or in northern regions – there might not be enough growing degree days remaining after the corn harvest to get a good cover crop established. What to do then?

One option is to start cover cropping at the beginning of summer, interseeding a cover crop into early corn. Dr. John Wallace, assistant professor of Weed Science at Penn State, recently spoke in a webinar about this practice.

Wallace suggested interseeding cover crops into no-till corn is a good tactic “where it’s difficult to establish cover crops consistently after corn harvest.”

“Prior to the herbicide era it was common to broadcast a cover crop during the last corn cultivation,” he added.

Of course, drilling is preferred to broadcasting, to ensure good seed-to-soil contact. Some farmers, though, have modified RoGators® to broadcast cover crops later in the growing season.

Wallace summarized recent investigations using high-clearance no-till grain drills in early corn. The best time for the practice, Wallace said, is V3 – V5 corn, to maximize weed control and fertility management. Interseed earlier than that and you could see a drag on corn yield.

“Ideally, you’re interseeding during the last pass through the field,” Wallace said. “You can combine interseeding with side-dressing or an herbicide application.”

Some farmers practice early season interseeding even when they have the conditions to establish a cover crop post-harvest. In addition to the above-listed benefits of having a cover crop, farmers have cited as their reasons for early cover cropping an increase in water infiltration as well as having a crop on hand to scavenge and retain applied fertility.

Drill interseeding cover crops into early corn

A high-clearance grain drill such as this one is ideal for interseeding into early corn. Photo courtesy of Bill Currin

When planting a cover crop in early corn, the crop will have less available light and possibly a reduced supply of water and nutrients. Thus, it’s important to choose a cover crop which will successfully establish and thrive in those conditions.

Recent work has shown that the best grass to use when cover cropping in early corn is annual ryegrass. Cereal rye will establish but has a hard time persisting through the warmer months. Other cover crops which have done well are medium red clover, crimson clover and daikon radish. It appears a cover crop mixture will outperform a single cover crop, but differences in management practices may also account for the variation seen in the results.

Other interesting findings have also appeared, such as the relative outperformance of daikon in drilled vs. broadcast applications and in higher fertility soils. However, when daikon is overexpressed as part of a cover crop mixture, there is less spring cover crop biomass.

There has been no sign in the investigations so far of any link between early cover cropping and a decrease – or increase – of corn yield (when the cover crop is planted when corn is V3 – V5). The most apparent conclusion is that farm management is what drives yields and overall success.

If you are interested in early interseeding of cover crops, Wallace does recommend doing so post-glyphosate. The risk of cover crop injury is high when there is still herbicide present in the soil.

Wallace is working on developing tables to show the relative sensitivity of cover crops to herbicides (with annual ryegrass being the baseline). For example, small-seeded legumes are highly sensitive to herbicides while winter cereals are less sensitive to herbicides than annual ryegrass.

Another step you can take to maximize the success of an early interseeded cover crop is in the selection of your corn variety. A variety with an upright architecture will allow more light to penetrate to the cover crop than a corn variety with an open architecture.

For more information on this topic and all questions related to drill interseeding cover crops into early corn, check with your Extension agent.

by Karl H. Kazaks