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16 steps to better corn-on-corn and continuous corn

1. Know your foe

The 5% to 15% yield drag in corn-on-corn and continuous corn sometimes can be lessened. To do that, though, you have to overcome excessive in-row residue that keys five issues.   

  • Poor seed placement. Residue stashed in the seed furrow at planting nixes seed-to-soil contact and results in uneven emergence.

  • Autotoxic compounds. “As residue decomposes, autotoxic compounds slow growth and reduce vigor of young corn plants,” says Jeff Coulter, University of Minnesota (U of M) Extension agronomist. “They can inhibit growth and vigor of young corn seedlings.”

  • Low soil temperatures. Excessive residue can lower soil temperatures below the optimal 50°F. recommended for planting. That delays emergence, early growth, and nutrient uptake.

That’s especially true in no-till corn-on-corn. “Soil temperatures can average 2°F. to 3°F. lower in the first three to four weeks after planting in no-till corn-on-corn when compared to disk-ripped corn-on-corn,” says Coulter.

  • Nitrogen (N) availability inhibition. Ever notice the crunch of cornstalks on just-harvested corn ground? That’s the sound of carbon. Long term, the carbon that ends up as soil organic matter from residue decay boosts soil’s water-holding capacity and other benefits.

Short term, though, it can create a fertility issue.

“That residue is a sponge in which the soil microbes are using N to feed on as they break down carbon,” says Jason Webster, Central Illinois Practical Farm research director for Beck’s Hybrids. “They use N, and if you don’t apply enough N next season, the corn plant will say, ‘Hey, what about me?’ ”

  • Increased disease. “This is especially true for diseases that survive on surface corn residue, especially anthracnose seedling blight,” says Coulter.

2. Don't show up late

Residue that causes late corn plant emergence will cause problems all season.

“Seeds need to imbibe 30% of their weight in water to germinate,” says the U of M’s Coulter. “Seeds surrounded by residue instead of soil will not imbibe water as quickly.”

The result is delayed and uneven emergence that creates plants unable to fully compete for water, nutrients, and light. Later on, these plants are late to silk. This boosts the risk of less pollen to make kernels, more stressful weather, and low soil-moisture levels during pollination.  

In the chart below, you’ll see early-emerging plants yield more than late-emergers in uneven emerging fields. “However, it is not enough to fully overcome the yield penalty from late-emerging plants,” says Coulter.

3. Reduce in-row residue 4 ways

  • Distribute residue evenly behind the swath of the combine.

  • Shred stalks and till early in the fall if a full-width tillage system is used.

  • Have good planter row cleaners that work well. “Removing residue from the row is critical,” says the U of M’s Coulter.

  • Monitor double-disk opener wear.

4. Make Cover Crops Do the Heavy Lifting

Dan DeSutter has successfully no-tilled corn into corn on his Attica, Indiana, farm for years. Among the tools he uses are cover crops that range from cereal rye to radishes.

Cover crops do an excellent job of spurring soil microbes that consume corn residue over winter, says DeSutter. Live roots provide habitat for microbes that break down surface organic matter. Less residue coupled with planter-mounted row cleaners make a good seeding environment.

“We plant into nice, clean garden dirt,” he says.

Meanwhile, remaining between-row residue provides a mulch that sustains biological activity throughout the growing season. He supplements the corn crop with nutrients several times during the growing season to make up for the N consumed by the residue-munching microbes.

5. Tile Your Fields

 “You have to have good drainage,” says DeSutter. “It doesn’t work worth a darn with poorly drained soils.”

6. Carefully Eye Stalk Breakdown Via Liquid N

That’s because it often doesn’t work. A Wisconsin trial found 100 pounds per acre of fall-applied 28% N did break down residue, but only one out of every three years.

University of Illinois (U of I) tests show no benefit by adding 50 pounds per acre of 28% N on stalks before tillage.

7. Target Aggressive Tillage Toward Poorly Drained Soils  

You’d think that aggressive tillage like deep-ripping would resolve excessive residue issues. That isn’t always the case, though.

U of I researchers have compared 8-inch-deep fall disk-chiseling vs. aggressive 12-inch deep-ripping. In some cases, deep-ripping increased yields. On average, though, little effect occurred. In some cases, shallow tillage worked better.

“More aggressive fall tillage is not always the answer,” says Coulter. “It may work better on poorly drained soils, but not on others.”

8. Partially Remove Residue

That’s what’s happening in a 2013 DuPont Stover Harvest Collection Program near Nevada, Iowa. Farmers receive compensation in a program that partially removes corn stover from their cornfields to fuel a cellulosic ethanol biorefinery near Nevada in exchange for a payment.

Partial removal under the program is key. Removing all corn stover would decrease residue breakdown and subsequent soil carbon as well as organic matter formation, says the U of M’s Coulter.

“On the other hand, if properly handled, corn stover removal and use of cover crops and green manure can build organic carbon levels,” says Coulter.

9. 40%

That’s the amount of annual corn stover removal that’s likely sustainable for continuous corn in today’s disk-rip systems, says Coulter.

That doesn’t apply to all tillage systems, though. If a more aggressive tillage system (like moldboard plowing) is used, even less residue should be removed, says Coulter.

10. Go With Your Best Ground

Excessive in-row residue is one reason why continuous corn and corn-on-corn yields drag. That’s not the only reason, though. Steps such as shrewd hybrid selection and fertility management are also needed.

“Growing corn-on-corn takes a whole new level of management,” says Bruce Battles, Syngenta solutions development manager. “It is not for someone taking the economy approach.

“Some of this is the right placement on the right acres,” he adds. “Don’t plant corn-on-corn in rough ground or low-yielding ground.”

11. Choose Hybrids Carefully  

A good hybrid is a good hybrid, regardless of whether you plant into corn or another crop. The same holds true for a poor hybrid.  

“If it doesn’t work locally in a corn/soybean rotation, it definitely won’t work in continuous corn,” says Syngenta’s Battles.

That said, check hybrid ratings for stress and emergence ratings for hybrids going into corn ground.

“All hybrids are rated on their ability to perform well in stressful environments,” says the U of M’s Coulter. “You need to look at this when you grow continuous corn. Choosing hybrids with good early emergence will likely result in more uniform emergence.”

That’s important, because corn in these systems tries to emerge through a corn residue mat under reduced tillage or no-till.

Coulter cites data from six trials in southern Minnesota showing that emergence falls 1% for every 10% increase in total surface-residue coverage.

Another way to deal with this is to boost seeding rates on high-residue fields, he adds.

“Don’t forget about disease,” says Battles. Additional residue provides a haven for disease-causing inoculum. Planting disease-resistant hybrids and applying fungicides, if needed, can curb disease.

12. Expect Corn Rootworm to Call

Corn rootworm thrives in a corn monoculture. In some cases, corn rootworm is resisting certain rootworm-resistant traits. Mixing up control measures such as traits, crop rotation, and soil insecticides is a good way to forestall resistance.

“No matter what technology is used, it all runs into trouble when just one mode of action is used,” reminds Jeff Hartz, Wyffels Hybrids director of marketing.

13. Beat Compaction With Patience

Residue prompts soils previously planted to corn to dry slower than those planted to soybeans. “You can get compaction issues if you till and plant in soils that are too wet,” says Emerson Nafziger, U of I Extension agronomist. .

Summer droughts also worsen sidewall compaction created by wet planting. “I will not plant wet,” says Jim Mitchell of his continuous corn strategy near Eaton, Ohio. “When I plant wet, I can see where it didn’t work later in the year.”

14. Plan For Sidedressing Delays  

Rainy day after rainy day can nix even the best-intended sidedressing plans.

The good news is more application options now exist. “There are hiboys that can go through 5- to 6-foot-high corn and spread coated urea,” says Syngenta’s Battles.

Mitchell equips his tractor with tall tires for late-season side-dressing of his continuous corn.

“Without them, I’m in trouble,” he says. “Two years ago, it was even wetter than this year. I ended up dropping 28% N with hiboys. It did an awful lot of leaf damage, but I did salvage the crop.”

15. Split N

Nitrogen immobilization by residue is a good reason why recommended corn-on-corn and continuous corn N rates are often at least 40 pounds per acre higher than corn following soybeans, says Coulter.

“Corn doesn’t take much N until it gets up to the V5 and V6 stages,” says the U of M’s Coulter. “Then it takes it up rapidly.”

There’s a risk that N applied preplant could be lost due to leaching or volatilization by this prime N need time. That’s why sidedressed applications that complement preplant and starter applications work well in these systems.  

“Typically, we see a response to split N,” says Beck’s Webster. Sidedressed N boosted yields by 11.4 bushels per acre in corn-on-corn over N-applied preplant in a 2009-2012 trial conducted by Beck’s Hybrids at Downs, Illinois. This strategy benefited corn following soybeans even more, as a 13.5-bushel-per-acre yield edge for sidedressing resulted. Averaged together, sidedressing boosted yields 12.4 bushels per acre and revenues $43.20 per acre.

16. Don’t Assume Starter Always Boosts Yields

Starter fertilizer containing N, phosphorus, and sulfur boosted early growth and sliced plant growth variability on continuous corn grown under reduced tillage in 2010-2011 U of M trials.  

Inconsistent yield responses resulted, though, says Jeff Vetsch, a U of M soil scientist. At a 2011 Rochester, Minnesota, site, 4 gallons per acre of 10-34-0 applied in-furrow boosted yields 4 bushels per acre. Yield boosts of 6 to 9 bushels per acre occurred at a Waseca, Minnesota, site in 2010 when soil scientists banded 12-0-0-26.

Other tests showed no response. Corn planted on poorly drained corn ground was more likely to respond than corn planted on better drained soils, Vetsch says.

If you apply starter, you don’t have to spend a lot of money on starter equipment for your planter.

A 2004-2006 U of M study found a surface-dribble band equaled the performance of a starter band placed 2 inches deep and 2 inches away from the seed.

“You don’t have to have heavy starter attachments on your planters,” says Vetsch. “You can just dribble it on.”

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