More northern Corn Belt farmers are planting continuous corn, and that means more hard-to-handle residue left in fields.

Higher plant populations, better-yielding hybrids, less aggressive tillage and the cold climate – which slows down decay – all increase the mounds of debris.

Surface residue lowers soil temperatures, hindering germination and early growth. Excess corn debris can also tie up nitrogen (N) and cause planting problems, reduced stands and more disease.

“Residue management is our No. 1 challenge with corn after corn,” says John Nelson, who farms with his son Jared at Hanska, MN. The Nelsons have a little over half of their 2,800-acre operation in continuous corn. “We’ve been tweaking our tillage and fertilizer for 10 years and we’ve learned a lot, but we still make mistakes.”

A 200-bu. corn crop creates more than 10,000 lbs./acre of residue. Here are some tips from experienced “residue managers” on how to handle all that trash.

*Consider your rotation.

For John Nelson, economics favor corn over soybeans. “I have a lot of high-pH soil, and soybeans don’t do well,” he says. But his land can produce 200+-bu. corn crops. Last year, his whole-farm average was 215 bu./acre.

In fact, throughout the northern Corn Belt, “There’s a comparative yield advantage for corn over soybeans that’s much higher than in the central Corn Belt states,” saysJeff Coulter, University of Minnesota Extension corn agronomist. Corn yields up north have climbed faster than soybean yields, and northern states appear “better suited to corn than soybeans when compared to other regions.”

Still, crop rotation typically increases both corn and soybean yields by 5-10%, Coulter notes. As an alternative to continuous corn, he suggests a corn-corn-soybean rotation.

*Size and spread residue evenly.

The Nelsons use a John Deere chopping corn head with stalk stompers to process corn stalks at harvesttime.

It’s really important to spread residue evenly, says Clyde Tiffany, a Pioneer Hi-Bred field agronomist in Minnesota. Combines with wide header widths may concentrate residue in swaths. Windrowed corn debris reflects more sunlight in the spring and slows soil warming, resulting in uneven emergence in rows where residue accumulated.

After harvest, Nelson uses a Case IH 330 vertical-tillage tool, at high speed, to size residue before disk ripping. Closely spaced wavy coulters shatter brace roots and tear up root balls, knocking the soil out of them, Nelson says.

Sizing residue aids incorporation and provides more entry points for fungi and soil microbes, the organisms that break down residue, Tiffany says.

Use fall tillage to speed up residue decomposition

*Use fall tillage to speed up residue decomposition.

Continuous corn responds more to tillage than corn after soybeans, Coulter says – especially on heavy soils.

Two decades of continuous-corn trials at the University of Wisconsin found that fall chisel tillage improved yields 5-8% for second-year corn, and 8-11% for consecutive years of corn.

However, tillage did not improve corn yields for first-year corn following soybeans.

“If you’re in a corn-soybean rotation, you can get by without tillage,” says University of Wisconsin Extension Corn Agronomist Joe Lauer. Even in second-year corn, it’s not always profitable to chisel plow, he says. “But when you get deeper into consecutive years of corn, there is an advantage to tillage.”

John Nelson follows vertical tillage on continuous-corn ground with a Case IH 870 disk ripper, equipped with shanks spaced at 24 in. and a harrow. His fall tillage operations leave about 40% residue cover for the winter. “The residue is fine so it breaks down better.”

Elkton, SD, farmer Spencar Diedrich has experimented with several types of tillage for continuous corn, which represents about 75% of his family’s operation. The Diedrichs don’t use tillage for soybeans, but have found corn-on-corn “tough to do without tillage.”

They tried fall strip-till, but had problems with residue blowing over the strips, slowing spring warm-up. They’ve gotten better results with full-width tillage, Diedrich says.

For several years, they used a Sunflower land finisher in the fall. Recently, they switched to a Wishek disk, which both chops and incorporates residue into the top 6 in. of soil. Fields that will be planted to corn again get two fall passes with the Wishek disk, if there’s time, at a cost of $8/acre/pass.

Move your fall tillage for continuous corn as early as possible, Coulter adds, so shredded residue has time to decompose. Soil microbes are most active at soil temperatures above 50° F.

*If you have a market, harvest some residue.

The addition of distillers’ grains to cattle diets offers an “excellent opportunity to use corn stalks as feed,” says Gregg Carlson, South Dakota State University plant scientist.

In cattle diets, distillers’ grains plus corn stalks provide about the same level of total digestible nutrients as corn grain. “This is a great opportunity to increase profitability and productivity,” he says, “especially if you put manure back on the field.”

Removing some residue raises yields, lets you reduce tillageand has agronomic benefits, too, Coulter says.

Illinois research found that grain yields for the following corn crop rose about 5% when half or all of the corn residue was removed the previous fall. Nitrogen requirements fell about 13%, and no-till yields were comparable to those with conventional tillage.

In continuous corn with disk-rip tillage, you can sustainably remove about 40% of residue, Coulter says. Choose productive fields with low erosion risk and rotate residue harvest among fields. Also remember that you will need to replace the nutrients in harvested stover, especially potassium.

Harvesting more corn residue than just the cobs is not usually sustainable in a corn-soybean rotation, or on erodible or droughty soils, Coulter adds.

*Skip N to break down cornstalks, but consider adding sulfur.

The Diedrichs of South Dakota used to apply a 28% UAN solution to corn residue in the fall to speed up decomposition, but decided it didn’t pay.

Midwest research confirms that adding N to corn stalks in the fall doesn’t accelerate residue breakdown, says Wisconsin’s Lauer. That’s because residue decomposition in the northern Corn Belt is limited by cold soil temperatures – not a lack of N. Treating corn stalks with N just adds unnecessary expense and leaching risk, he adds.

Minnesota grower John Nelson applies 5 gal./acre of ammonium thiosulfate in a band over the top of the corn rows at planting. “Sulfur deficiencies are common now,” Coulter says. In Minnesota research trials, “We’re seeing an early season response to sulfur in continuous corn, with taller, larger and more uniform plants.”

*Use row cleaners.

Row cleaners on the planter are essential tools for effective residue management in continuous corn, Pioneer’s Tiffany says. A 6-10-in. residue-free band at planting improves seed-to-soil contact and raises soil temperatures in the seed zone.

Does Bt corn residue break down more slowly?

There’s a widespread perception that Bt-corn residue resists decomposition, resulting in more surface trash. But a recent series of field experiments found no differences in how rapidly Bt and non-Bt corn residue decayed.

This matters, says Michael Lehman, a microbiologist at the USDA-ARS North Central Agricultural Research Lab in Brookings, SD, because “if more aggressive tillage is needed to manage tougher residue, we will expect a cost in more soil erosion.”

Lehman led three field studies and one greenhouse trial that compared residue decomposition rates for Bt hybrids and their related non-Bt isolines. The trials included genetics from several seed companies. Corn residue was compared from fields with and without corn rootworm and European corn-borer infestations.

The corn residue was chopped and buried, simulating the effects of combining, chopping and fall tillage. “We found no differences in decomposition of corn residue linked to Bt genes,” Lehman says. Nor were there differences in stalk strength related to the presence of Bt genes, he says.

Still, Lehman adds, “I don’t discount farmers’ observations.” It’s likely that the apparent persistence of Bt-corn residue is related to the steady increase in the total amount of residue produced as a result of higher yields and plant populations, he says. Another factor could be the prevalence of hybrids selected for traits that keep stalks standing longer, he adds.