Guidance When Using Corn as a Cover Crop

This year, traditional cover crop seed is hard to find. However, corn and soybean can be considered a cover crop (click here and here). Corn is deep-rooted and by the end of the growing season can produce significant residue even when planted in July. The first thing you must do, however, is talk to your crop insurance agent and make no decisions without their input.

"Farmers taking the full prevented plant indemnity should note that they cannot ever harvest the cover crop for grain or seed. RMA rules allow, only after September 1, grazing and harvest as hay (for bedding or feed) and now for silage, haylage or baleage. If a farmer wants to harvest it as grain or seed, then they should declare it as an alternative crop and only collected the partial (35%) prevented plant indemnity."  --- Paul Mitchell, UW Ag Economist

The end of the late planting period is set by USDA-RMA (Risk Management Agency) and is posted for most of Wisconsin as June 25 for corn grain and June 30 for corn silage. A farmer is not allowed to take the full prevented plant indemnity, using the same crop as a cover crop before these dates. If planted before these dates, the farmer should report it as late planted with a reduced guarantee.

As corn planting moves into June, yield swings (risk) increases. Some years can result in good grain yields, other years not so much. Early June planting dates often produce high yielding corn silage of good quality. Late June planting dates are difficult to predict for grain or silage production. Planting corn in July rarely results in adequate grain production so silage quality is poor. Corn makes an excellent "emergency" forage when planted in July. During 2005 and 2006, corn planted July 1 had forage yields ranging from 5.9 to 7.7 Tons Dry Matter / Acre (T DM/A). For corn planted July 15, forage yields were 3.5 to 5.6 T DM/A, and corn planted July 31 forage yields were 0.7 to 2.8 T DM/A.

The following agronomic guidance is given when growing corn as a cover crop. The goal of a cover crop is to protect the soil from erosion (wind and water), to improve water quality by capturing nutrients, to build organic matter, and to suppress weeds. Ultimately the decision to use corn as a cover crop is the cost of production. Typically, it would cost $400 to $450 per acre to establish corn.

Practices that maintain ground cover or establish a crop canopy quickly include:

• Seed: Conventional hybrids and open-pollinated varieties are less expensive than bio-engineered hybrids. Neither seed nor grain from bio-engineered corn hybrids can be used as cover crop seed. Upon purchase of bio-engineered hybrids, farmers sign a contract that: 1) limits usage of grain to specific end product channels, 2) restricts ownership of bio-engineered traits, and 3) requires a refuge (stewardship). There has been some discussion of using the F2 (grain) of 2018 production ("bin-run" seed/grain). A 10-20% grain yield drag would be expected for F2 seed, however, little grain yield is expected anyway with July planting dates. Using bin-run grain as seed might be possible for conventional hybrids and open-pollinated varieties. Check seed labels and grower agreements to make sure. Again, it is illegal to use bio-engineered hybrids. For specifics about contracts for bio-engineered hybrids, see https://www.agcelerate.com/Home.

Performing any ONE of the following practices, if different from the current on-farm commercial production practice, indicates that the objective of growing corn for grain has changed to the objective of growing corn as a cover crop.

• Plant population and seed costs: Higher populations lead to faster ground cover and helps with weed suppression. Minimum populations upwards of 35,000 plants/A are needed for corn as a cover crop. However, seed costs can also be prohibitive for higher populations.
• Narrow row spacing: Corn is a row crop. Using a narrower row corn planter (< 30-inches), twin-row planter, or a grain drill can lead to faster ground cover by the corn canopy and weed suppression. Criss-crossed rows can lead to quicker canopy cover. 
• Crop rotation: Rotating crops helps with interrupting pest cycles and promotes early growth and quicker canopy coverage. The choice of the cover crop this year should be based upon the subsequent crop intended next year. For example, if soybean is planned for the field next year then corn (or some grass crop) should be the cover crop this year.
• Planting into residue: Seeding into fields with > 30% residue provides some ground cover between planting and canopy establishment. 
• Pesticides: Herbicides should be used to help with weed control. Use care about pre-grazing and/or pre-harvest restrictions after September 1.
• Nitrogen: The most important nitrogen applied to corn is the first 40 to 60 lb N/A. Even this may not be needed if N credits can be taken. Reducing N rate would improve cost of production, especially since little grain is expected.

July plantings rarely result in grain production in Wisconsin. A killing frost usually occurs during September or early October. If grain is produced and kernels develop beyond the milk to dough (R3-R4) stage then the crop should be cut with a haybine.

Further Reading

Conley, S., J. Lauer, and P. Mitchell. 2019. Soybean and Corn are Considered Cover Crop Options in WI

Mitchell, P. 2019.  Can I Use Corn or Soybeans as a Cover Crop on Prevented Plant Acres?

Mitchell, P. 2019.  Crop Insurance: Late and Prevented Planting and Replant