Spring management of cover crops
Spring management of cover crops is as varied as farming operations across Minnesota. A farmer’s plan of action will largely be determined by two things:
The reason for using cover crops in the first place.
The specific cover crops planted.
A farmer who wants to graze livestock in the spring may have planted winter cereal rye as a cover crop. Spring management in this situation will likely include letting the cattle graze the winter cereal rye for a few weeks, terminating the cover crop with an herbicide or tillage, and planting a cash crop that can successfully be grown with a late May planting date.
A second example might be a corn or soybean farmer who’s new to cover crops and interested in interseeding annual ryegrass and red clover into standing corn in mid-June at the V6 stage of corn (six corn leaves have visible leaf collars).
While red clover regularly overwinters in Minnesota, annual ryegrass winter survival depends on planting date and winter weather conditions. If planted in June, there’s a good chance that annual ryegrass will overwinter to some extent.
Spring management in this situation would likely include waiting until air and soil temperatures reach the requirements on the herbicide label for application and when the annual ryegrass and red clover ideally are 4 to 8 inches tall.
Cover crop termination
Cover crops that typically don’t overwinter include spring small grains (e.g., oats, spring wheat), some legumes (e.g., crimson clover, field pea) and some non-leguminous broadleaves (e.g., buckwheat, oilseed radish).
However, be aware that some winter cover crops that are normally winter-killed may survive into the spring. For example, some cold-tolerant cover crops like turnips may overwinter if there’s plenty of snow cover. There may be a few scattered plants or a patch in a protected area.
Another possibility is spring germination of seed that didn’t germinate in the fall. When this occurs, handle the cover crop as if it were a winter-hardy cover. Winter-hardy cover crops, including winter cereal rye, winter wheat and hairy vetch, go dormant over the winter and begin growing again in the spring.
Poor fall growth or harsh, open winters may result in winter-kill for some of these plants. Spotty or limited spring growth can be especially common with hairy vetch.
Approaches to termination
If cover crops are winter-hardy, have a plan in place that includes chemical and/or mechanical termination in the spring.
Chemical termination by a nonselective herbicide is often the choice for conventional farmers who need to manage winter-hardy cover crops. A general guideline for successful termination is to spray when the cover crop is about 4 to 8 inches tall.
Younger, smaller plants are easier to kill and tend to have a lower carbon-to-nitrogen ratio, which results in faster decomposition (Table 1). Cool spring temperatures can lead to cover crops that aren't actively growing. In this case, they’d have trouble taking up the herbicide and control can be compromised.
Table 1: Approximate carbon-to-nitrogen ratios of common crops and cover crops
|Organic material||Carbon-to-nitrogen ratio|
|Rye cover crop (at anthesis)||37:1|
|Rye cover crop (vegetative)||26:1|
|Young alfalfa hay||13:1|
|Hairy vetch (vegetative)||11:1|
A second herbicide application may be needed to fully control the cover crop if:
Cover crops are allowed to grow longer in the spring in order to graze it or to take up more nitrogen.
The spring weather isn’t cooperating.
Always consult product labels before using an herbicide and check for any restrictions to ensure the application will not impact your cropping rotation or forage plans.
Mechanical methods of cover crop termination primarily include using tillage equipment, such as a roller/crimper or a mower. You can use these methods alone, in combination with one another, or with an herbicide.
Different spring tillage equipment options can affect termination success. A field cultivator operating at a 3- to 4-inch depth will cut most cover crop roots and bury the plant, resulting in better termination.
This isn’t necessarily true for coulter carts or vertical tillage equipment, because these move soil up and down and have little effect on cover crop or weed termination. One pass with a piece of tillage equipment may not result in enough soil and root disturbance to kill the cover crop, so be prepared to take two passes, if needed.
A roller crimper or a mower can also successfully terminate winter-hardy cover crops. However, these methods have the best chance for success when cover crops have reached maturity, i.e., the flowering or heading stage of growth.
This often puts the timing of these two termination methods into late-May. If you use a roller crimper for cover crop termination, it’ll be important to plant the cash crop in the same direction and use properly calibrated equipment that has sufficient attachments or down-pressure to move aside or cut through the residue.
The amount of residue left in the spring will depend on which cover crops you used and when you planted them.
Brassicas and legumes break down and begin decomposing faster than grasses because of a lower carbon-to-nitrogen ratio in the plant material.
One exception to this is if the brassicas are allowed to mature and flower. In this case, they’ll become stemmy, increasing the amount of time it takes to decompose.
The age of the cover crop stand also affects decomposition rate. The earlier the cover crop is planted, the more mature it will be at termination. This results in a higher carbon-to-nitrogen ratio and slower decomposition.
Additionally, one of the keys to spring management of cover crop residue is planter set-up. Calibrate your planter so it can sufficiently handle the cover crop residue situation.
The planter may need to be recalibrated, not just between fields, but within the field as well. This is especially true in areas with measurable changes in residue type or amount.
Be on the lookout for potential spring pest issues in cover crop fields, particularly with winter-hardy cover crops.
Make a point to scout cover crop fields and/or be prepared to terminate as soon as the weather allows.
The general recommendation is to wait seven to 14 days after cover crop termination before planting the year’s cash crop. This is mainly to allow some time for the cover crop residue to begin breaking down and for surface moisture to recharge.
However, there have been cases when farmers successfully planted into standing cover crops or planted within days or hours of spraying. Keep in mind that the USDA-NRCS Cover Crop Termination Guidelines specify termination timing for those involved in USDA programs such as EQIP or crop insurance.
The USDA Risk Management Agency website has additional information about cover crops and crop insurance.
One of the best sources of cover crop information is experience. Contact any neighbors, crop consultants, agency personnel or Extension educators with experience in managing cover crops. Most people with cover crop experience are more than willing to share what they have learned.
Termination guidance from other Extensions
Reviewed in 2018