It’s the right time for cover crops

Nearly 90,000 acres of cover crops were planted in Iowa in the fall of 2012. That estimate is based on data from several sources including sales figures from major cover crop seed companies and cost-shared acres through the USDA Natural Resources Conservation Service’s EQIP program, and the Iowa Department of Ag and Land Stewardship’s state cost-share funding.

Not included in that estimate are many farmers who didn’t take advantage of cost-share funds but added cover crops to their farming systems through saved seed or other outlets.

Cover crops protect soil from wind and water erosion, and capture nitrogen that can otherwise leach from the soil and pollute nearby water sources. According to the state of Iowa’s Nutrient Reduction Strategy Science Assessment, on average cover crops can reduce nitrogen loading by 28% and phosphorus loading by 50%.

Goals to protect Gulf

Meeting the state’s ambitious goal of a 45% reduction in the loss of nitrogen and phosphorus to the Gulf of Mexico seems reasonable when cover crops are added to the equation. However, while immensely beneficial to soil and nutrient protection, winter small-grain cover crops may have a negative impact on corn yields. Commonsense management is vital when adding this conservation practice to a farm.

In 2010, six locations measured an average 12-bushel-per-acre reduction in corn yield following a winter rye cover crop. However in 2009, 2011 and 2012, no reductions in corn yield were measured following a winter rye cover crop.

Soybean yield in 2009, 2011 and 2012 following a winter rye cover crop was the same as if planted following no cover crop. In 2010, soybean yield was 4 bushels per acre greater when following a cover crop.

In 2011 near Clutier in east-central Iowa, farmer Mark Pokorny saw a significant increase in yield of his non-GMO soybeans when they were planted following a cover crop. The cover crop residue controlled weeds in his soybeans, resulting in an 8-bushel-per-acre yield increase.

The possibility of negative effects could discourage farmers from adding a cover crop as a conservation practice to their farms in the fall before a corn crop.

Legume cover crops fix nitrogen and have the potential to decrease a cover crop’s negative impact on corn yield. However, they haven’t been studied or used extensively in Iowa, so little information exists about establishing these nitrogen-producing cover crops.

Legume cover crops in Iowa

Because a large majority of cover crop acres in Iowa are seeded with airplanes or helicopters, finding a legume cover crop that works in this system is important. Members of Practical Farmers of Iowa wanted to learn more.

The PFI farmers participating in cover-crop trials overseeded 20 cover crop species, including pure and mixed grasses and legumes, to determine which species would have the greatest success.

Seed disbursement

Seeds were broadcast by hand, to mimic overseeding with an airplane. Cover crops were planted when soybeans had their first yellow leaves or corn was nearing black layer.

Plots were 25 feet long and 7.5 feet wide, and two replications of each variety were planted. Ground cover measurements were collected before “winter” snow was predicted at each farm or between mid-November and mid-December.

At Carroll in western Iowa, farmer Art Behrens planted the different cover crops into both standing corn and soybeans, and collected ground cover data on Nov. 17.

As expected, the winter small grains had a greater percentage of ground cover compared to legumes when broadcast-seeded into a standing crop. Still some legume species (winter lentil, common vetch and hairy vetch) also had significant growth under the soybean or corn canopy. Information from this study will help other farmers decide which cover crops may be successful if seeded with an airplane.

Spring cover suggestions

Ten farmers around Iowa have completed year four of an on-farm cover crop research project. Cover crop specialist Sarah Carlson cites their answers to the following questions regarding spring management of fall-seeded cover crops.

• When is a cover crop ready to be killed? Last spring, farmer Tim Smith from Eagle Grove was concerned if the rye was dead after spraying it with glyphosate. As shown in the photo above, the rye had major growth in spring 2012 and was actively growing at time of herbicide application.

At a recent PFI meeting, Doug Alert from Hampton said, “I make sure the winter rye cover crop is killed before it gets to the top of my redwing boots. It’d better be dead by then.” That’s good advice. You should kill a winter small-grain cover crop eight to 10 days before planting corn or a couple days before planting soybeans.

• What about soil moisture? Central Iowa farmer Dick Thompson says if moisture is limiting, get the cover crop killed early. A small-grain cover crop needs water to grow, although it doesn’t use as much water as a corn plant. From March to May, when cover crops are growing, water is usually available.

However, if the cover crop has grown until near the time when spring rains shut off, establishing a cash crop could be difficult. Play it safe; if your area is moisture-deficient at the end of April, make sure the cover crop is killed.

• What about grazing? Silage harvest? Many livestock producers are seeing the benefits of cover crops providing cheap feed for livestock, while also protecting their soils. It is advisable to graze before or following the spring freeze-thaw period, to minimize the risk of damage to soil structure and compaction. Cover crops may be grazed or hayed prior to reaching a “bud stage” or at the very latest before May 10, based on current crop insurance rules.

However, you should always check with your crop insurance agent regarding USDA Risk Management Agency rules on cover crops to ensure no surprises. Grazing into early May needs to be balanced with stage of plant growth, if a producer is planning to plant and insure a cash crop.

• Where can I find out more? To learn more about what other farmers in Iowa do to add cover crops to their farm, attend one of the nine spring field days organized by Practical Farmers of Iowa and the Iowa Learning Farms. Visit a farm. See the cover crops. Learn more about this practice and how it could fit into your farming system.

Or contact PFI to conduct an experiment on your farm. Last year more than 50 farmers did research with PFI, and the majority of those were focused on testing cover crops on their farms.

Contact Sarah Carlson at


TIMING: Last spring this rye cover crop had significant early growth at time of herbicide application. “You should kill a winter small-grain cover crop eight to 10 days before planting corn or a couple days before planting soybeans,” says PFI’s Sarah Carlson.

This article published in the March, 2013 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2013.