Spring has sprung in the majority of Minnesota. It's now time to manage cover crops that were planted last summer or fall. Spring management of cover crops is as varied as the different farming operations across Minnesota. The plan of action any given farmer decides to do primarily depends on two things: 1) His or her reasons for using cover crops in the first place, and 2) the specific cover crops used.
Termination of cover crops
Winter-killed cover crops such as spring small grains (oats, spring wheat), some legumes (Crimson clover, field pea), and some non-leguminous broadleaves (buckwheat, oilseed radish) will have died over the winter. However, be aware that some winters may result in situations that allow cover crops that normally winter-kill to survive into spring. Some cold tolerant cover crops, turnips for example, may overwinter if there is plenty of snow cover. You may see a few scattered plants or possibly a patch in a protected area. Another possibility is spring germination of a seed that didn't germinate in the fall. If either one of these situations occurs, treat it like a winter-hardy cover.
Winter-hardy cover crops like 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 some plants not surviving the winter, so you may see spotty or limited growth. However, if you have any winter-hardy cover crops, you need to have a plan in place and be prepared with chemical or mechanical termination.
Chemical termination by a nonselective herbicide is often the choice for conventional farmers that need to manage winter-hardy cover crops. A general guideline for successful chemical termination is to spray when the cover crop is about 4-8 inches tall. Younger, smaller plants are easier to kill and tend to have a lower carbon to nitrogen ratio for faster decomposition. Cool spring temperatures can lead to cover crops that aren’t actively growing; if the covers aren’t actively growing then they will have trouble taking-up the herbicide and control can be compromised. If the spring weather is not cooperating or if you made the decision to allow the cover crop to grow taller, a second herbicide application may be needed to fully control the cover crop. Always consult product labels before using an herbicide and check for any restrictions to ensure use of the product will not impact your cropping rotation or forage plans.
Mechanical methods of cover crop termination primarily include use of tillage, a roller crimper, or a mower. These methods can be used alone or in combination with each other or an herbicide.
Different spring tillage equipment options can affect the termination success. A field cultivator operated at a 3-4 inch depth will cut most cover crop roots and bury the plant resulting in better termination. This is not necessarily true for coulter carts or vertical tillage equipment, since they move soil up and down which has little effect on cover crop, or weed, termination. One pass with a piece of tillage equipment may not be enough soil and root disturbance to kill the cover crop so be prepared to use two passes if needed.
A roller crimper or a mower can also successfully terminate winter-hardy cover crops. However, these methods are successful when the cover crops have reached maturity (flowering or heading stage of growth). This often puts the timing of these methods of termination into late-May. If you choose to use a roller crimper, be sure to plant in the same direction, and use a properly calibrated planter that has sufficient attachments or down-pressure to move aside or cut through the residue.
Cover crop residue management
The amount of residue left in the spring will depend on which cover crops were used and when they were planted. Brassicas and legumes begin decomposing and breakdown faster than grasses because of a lower carbon to nitrogen ratio in the plant material. The age of your cover crop stand will also affect decomposition. The earlier you planted the cover crop, the more mature the cover crop is at termination. This results in a higher carbon to nitrogen ratio and slower decomposition. The key for spring management of cover crop residue is planter set-up. Be sure to calibrate your planter so that it can sufficiently handle the cover crop residue situation. This may mean that you will need to re-calibrate the planter, even within a field if there are areas with measurable changes in residue type or amount.
Additional things to keep in mind
- Be on the lookout for potential spring pest issues in cover crops fields, particularly with winter-hardy cover crops. Make a point to scout your cover crop fields and/or be prepared to terminate as soon as the weather allows.
- It is normally recommended to wait 7-14 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 the surface soil moisture to recharge. That being said, there are farmers that successfully plant into standing cover crops or plant within days or hours of spraying. Keep in mind, however, that the USDA NRCS Cover Crop Termination Guidelines specify termination timing for those that are involved in USDA programs such as EQIP or crop insurance: http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/climatechange/?cid=stelprdb1077238#Guidelines
- For additional information regarding cover crops and crop insurance, visit the Risk Management website for their Frequently Asked Questions: http://www.rma.usda.gov/help/faq/covercrops2016.html.
One of the best sources of cover crop information is experience. If you have access to neighbors, crop consultants, agency personnel, or Extension Educators with experience managing cover crops, be sure to contact them. The majority of people with cover crop experience are more than willing to share what they have learned.