Wallaces Farmer

When and how to terminate a cover crop is a popular question as corn planting time draws near

Rod Swoboda 1, Editor, Wallaces Farmer

April 8, 2016

7 Min Read

As the number of Iowa farmers using cover crops continues to grow, it’s important to help make sure these farmers have a successful experience. The Iowa Department of Agriculture earlier this week released a list of spring management tips and information for farmers who are new to growing cover crops.


“We continue to see significant growth in the number of farmers using cover crops on their farm and also the total acreage of cover crops in the state. As a result, farmers are seeing the benefits firsthand around reduced erosion, improved water quality and soil health benefits,” observes Iowa Secretary of Agriculture Bill Northey. “With good soil moisture and warm spring weather we are seeing very good cover crop growth.  This makes good management this spring even more important.”

Let cover crop grow as long as possible to gain most benefit

It’s important to allow the cover crop to grow as long as possible to maximize the benefits of reducing erosion and improving soil health. That was the message Barb Stewart gave to about 50 farmers attending a cover crop field day April 5 at the Gordon Wassenaar farm near Prairie City in central Iowa. Stewart is the state agronomist for USDA/NRCS in Iowa. The field day was sponsored by NRCS, the Iowa Corn Growers Association and Jasper County Farm Bureau.

“Letting the cover crop grow as long as possible before terminating it in the spring to plant your corn or soybeans will help you get the most benefit from the cover crop,” says Stewart. “Of course, this is typically easier to do if you are planting soybeans after cover crops because of the later planting date and there’s less potential impact on soybeans following a winter cereal grain. For corn, it’s important to terminate cover crops 10 to 14 days ahead of planting. More experienced users of cover crops may be more comfortable with closer termination windows -- that is terminating the cover crop close to corn planting. Some farmers have tried terminating the day before planting or the day of planting, with variable results.”

Six timely tips to help make cover crop decisions this spring

The following information was put together with the help of the Iowa Cover Crop Working Group, which includes representatives from the Iowa Department of Agriculture & Land Stewardship, Practical Farmers of Iowa, Iowa State University, Iowa Learning Farms, USDA’s Agriculture Research Service and NRCS. More information about putting cover crops to work in your farming operation can be found at cleanwateriowa.org/farm-practices.aspx  or at extension.iastate.edu/ilf/content/cover-crop-resources

1) Evaluate for winter kill – The mild and wet winter we’ve just had in Iowa, coupled with an early spring has provided near optimal conditions for cover crop growth. Cover crop species that may normally winterkill may have over wintered. It’s important to assess how cover crop fields survived the winter so you can make informed management decisions. If the aboveground cover crop is brown and near the soil surface and no green plant material is present, then your cover crop has winterkilled.  Cover crops such as tillage radishes and oats typically winter kill and then no additional spring management is needed. Other cover crops, such as winter rye or cereal rye, winter wheat, triticale and barley, consistently overwinter in Iowa. 

2) Termination options – Herbicides, tillage or a combination of the two can be used to effectively manage cover crops in the spring. Keep in mind any tillage will reduce the effectiveness of the cover crop residue to protect against erosion and suppress weeds. Some additional considerations for both methods of termination follow:

Herbicide: For successful termination using herbicide, make sure the plant has "greened-up" and has enough living surface area for the herbicide to work. Experienced farmers suggest spraying during the middle of the day and, if possible, spray when air temperature is at least 45 or 50 degrees F. Unless you have experience, separate your nitrogen application from a "burndown" herbicide application.

Tillage: Terminating cover crops with tillage can be effective, but may take more than one tillage pass. Wet periods can delay tillage to terminate cover crops and wet conditions following tillage can allow cover crop plants to survive tillage operations.  Also, tilling a cover crop to terminate it eliminates the erosion prevention benefit that the cover crop would usually provide in the early part of the growing season.

3) Consider nitrogen needs – Cover crops effectively sequester nitrogen and as the plant residue breaks down it will release its nutrients, making them available for the crop later in the season when it is most needed. However, there is the potential for lower available nitrogen early in the growing season, especially following an overwintering grass cover crop like cereal rye. To protect the yield of the corn, farmers growing corn after a cereal rye cover crop may want to apply 30 to 50 pounds per acre of nitrogen at or near corn planting. This is not additional nitrogen, but within the farmer’s total fertilizer program.

4) Know crop insurance requirements – Crop insurance rules state that a cover crop in Zone 3 (western third of Iowa) must be terminated by the day of cash crop planting. A cover crop in Zone 4 (eastern two-thirds of Iowa) must be terminated within five days of cash crop planting. If using no-till, you should add seven days to either scenario. More information about insurance requirements can be found at rma.usda.gov/help/faq/covercrops2016.html.

5) Start planning now for cover crop needs this coming fall – Determine what cover crop(s) work with your current or planned crop protection program. Some residual herbicides have carryover restrictions for certain species of cover crops. Consult with your agronomist and/or cover crop seed representative to look at your specific management system with the integration of cover crops. Additional information can be found at weeds.iastate.edu/mgmt/2015/CCherbicides.pdf

6) Consider participating in the Conservation Technology Information Center’s annual cover crop survey – The CTIC conducts an annual cover crop survey of all farmers, whether they plant cover crops or not. Farmers can take the 10 to 15 minute survey completely anonymously and it helps guide policy, research and education on cover crops nationwide. The survey is available at conservationinformation.org/Cover%20Crops.

“Hopefully these tips and the information resources that are available statewide will help farmers have success as they manage their cover crops this spring. We want farmers to have a successful experience and be encouraged to try cover crops again in the future,” says Northey.

Background information on the Iowa Water Quality Initiative

The Iowa Water Quality Initiative was established in 2013 to help implement the Iowa Nutrient Reduction Strategy, which is a science and technology based approach to achieving a 45% reduction in nitrogen and phosphorus losses to streams, rivers and lakes in Iowa. The nutrient reduction strategy brings together both point sources, such as municipal wastewater treatment plants and industrial facilities, and nonpoint sources, including farm fields and urban stormwater runoff, to address these issues.

The initiative seeks to harness the collective ability of both private and public resources and organizations to deliver a clear and consistent message to stakeholders to reduce nutrient loss and improve water quality.

More and more farmers are using nutrient reduction practices       

As part of the initiative, last fall 1,800 farmers committed $3.5 million in cost share funds to install nutrient reduction practices on farms in each of Iowa’s 99 counties. The practices that were eligible for this funding are cover crops, no-till or strip till, or using a nitrification inhibitor when applying fall fertilizer.

Participants include 980 farmers using a practice for the first time and more than 830 past users that are trying cover crops again and are receiving a reduced-rate of cost share help. Farmers using cost share funding contribute 50% or more of their own money to the total cost of the practice. 

Partnering organizations are helping provide some of the funding

There are also currently 45 existing demonstration projects located across the state to help implement and demonstrate water quality practices through the initiative. This includes 16 targeted watershed projects, seven projects focused on expanding the use and innovative delivery of water quality practices and 22 urban water quality demonstration projects. More than 100 organizations are participating in these projects. These partners will provide $19.31 million dollars to go with over $12 million in state funding going to these projects.

More than $325 million in state and federal funds were directed to programs with water quality benefits in Iowa last year. This total does not include the cost share amount that farmers pay to match state and federal programs, nor does it include funds spent to build practices without using government financial assistance.

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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