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Cover crops are often planted to build soil health and improve soil conservation. However, following grain corn, cover crops often have limited time to establish and provide intended agronomic benefits. Interseeding a cover crop earlier in the growing season provides more time for the cover crop to establish.

Interseeding is defined as planting a cover crop early in the season when the corn is between V4-V8 growth stage. In contrast, cover crop overseeding typically occurs near harvest and the cover crops are seeded using specialized high-clearance equipment or aerially applied.

Goal of Cover Crop

A goal is needed to achieve maximum cover crop success. Cover crop species often have common benefits but each species may contribute more of one benefit over another.

Several cover crop goals include enhancing nutrient cycling, improving soil health, surpassing weed growth, supporting beneficial insects and pollinators, and providing supplemental forage. Cover crop interseeding can be part of a long-term strategy for soil improvement. However, one year of interseeding will have little effect on soil health. Long-term and continual use of cover crops combined with soil conservation practices may lead to improvements in the soil condition.

Species and Establishment

Wisconsin research has demonstrated success with red clover when interseeded into V5 growth stage corn. Interseeded red clover plots have resulted in no significant difference in grain yield when compared to a non-interseeded plots at the Arlington and Lancaster Agricultural Research Stations. This research has occurred over the past four growing seasons.

Red clover was seeded with a modified no-till drill at university recommended rates and depths. The modified no-till drill ensures good seed-to-soil contact, which improves interseeding success when compared to broadcast seeding.

Cover crops can be interseeded using specially made equipment, fertilizer spreaders, and air-flow equipment, however, higher seeding rates are necessary for success. In row-cultivated corn, cover crops should be interseeded at the last cultivation. Cover crop seeding rate, soil moisture levels, and environmental conditions should be considered prior to seeding the cover crop with a cash crop.

Interseeding cover crops into stressed corn or during dry growing conditions may result in reduced corn yield.

Many cover crop species may work in an interseeding system, however, experimentation in any unproven species may result in reduction in yield, future cover crop management issues, and lack of desired cover crop performance.

Winter rye, radish and annual ryegrass have been interseeded in Wisconsin with mixed success. Crimson and berseem clover, oats, and peas have not been successful in University trials. Corn variety and plant population may impact cover crop establishment due to light competition.

Considerations for Successful Interseeding

Beyond cover crop species and seeding method there are several more considerations for interseeding. The herbicides previously applied on the desired field for interseeding may dictate whether interseeding is possible or not.

In general, residual herbicides may reduce cover crop growth. Interseeding and using residual herbicides is not impossible but is challenging. If the interseeded cover crop may become a supplemental forage crop, rotation restrictions of the herbicides used in the crop rotation must be known.

Herbicide resistant weed management should be considered when planning herbicide applications. The field should be weed free prior to interseeding. The cost of the herbicide program, cover crop benefits, and resistance management should all be considered.

To prevent the cover crop from becoming a weed the following growing season, a management plan is needed. The simplest solution is to plant a cover crop that will winterkill, however, most of the species that have shown success in an interseeded system will over-winter.

In these cases, a termination plan is needed, and cover crop termination method is species dependent. Tillage is not a recommended termination practice unless the cropping system has limited termination options. Frequent tillage can degrade soil health and many cover crop species may require multiple tillage passes for termination.

Mowing and forage harvest may slow and delay cover crop growth, but typically do not result in cover crop termination. A spring burndown herbicide application will provide termination if applied under ideal weather conditions and the cover crop is actively growing.

Finally, talk to your crop insurance agent before interseeding. Cover crops for soil conservation purposes need to be established in a way that does not affect the harvest and yield of the cash crop.

For more information email, dhsmith@wisc.edu. Wisconsin cover crop recommendations can be found at https://fyi.extension.wisc.edu/covercrop/

Smith is the Southwest Regional Specialist of the Nutrient and Pest Management Program for the University of Wisconsin-Madison College of Agricultural and Life Sciences and Division of Extension
 

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