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Residue: Too much of a good thing

Farmers are getting slammed with a triple whammy (or too much of a good thing) when it comes to crop residue, particularly that from corn.

Bt hybrids bred to withstand lodging and the increased use of foliar fungicides have resulted in stalks that resist decomposition.

Ever-increasing plant populations and corresponding fertilization programs are boosting both yields and the amount of stover a crop produces.

Compounding both situations is the trend to more corn-on-corn. The result is a bounty of crop trash that, if left unattended, can spell trouble next spring.

“Generally, excess residues tend to be a problem in the northern U.S. and Canada. Warmer temperatures in the south promote winter degradation,” explains Steven Butzen, Pioneer Hi-Bred.

Adam Heimer of John Deere cautions there is no single solution for dealing with increased residue. “It starts with the combine doing a good job of processing trash and a strategic tillage program,” he says.

On the other hand, University of Nebraska ag engineer Paul Jasa says crop residue disappears too fast for his preferences. “In terms of catching moisture (in snowfall) and stopping soil erosion, residue is an asset,” he says.

Following are six management tips to help you tame your trash.

1. Aim for 80% head-width distribution

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Even distribution of trash behind the entire width of a combine's head is the key.

An arsenal of tools can be brought together to battle against excessive residue. Two such tools are full-bodied residue-management systems and more aggressive heads. Discover a step-by-step guide to keeping choppers fine-tuned on page 35. Corn heads that process (chop, chew up, or crush stalks) are discussed on page 36.

“When it comes to residue management at the combine, the key is to spread it evenly behind the entire width of the head or platform whether running in corn, soybeans, or small grains,” recommends Kim Cramers of John Deere.

Situations where a narrow strip or a windrow of residue is being left directly behind the combine are a recipe for trouble next spring, warns Bob Wolkowski, a University of Wisconsin agronomist.

Wolkowski uses a rule of thumb for distribution where residue is spread across a minimum of 80% of the width of the head. If that is not occurring, he recommends upgrading the combine with a more aggressive residue chopper.

“Generally, farms don't spread wide enough,” says Phil Needham of Needham Ag Technologies. “You've absolutely got to spread evenly as well. We've seen examples where a heavy band of residue right behind the combine can cause a decrease in stands by 20% to 30% in no-till situations.”

Options abound when it comes to residue systems on combines. Some manufacturers are now offering three system options, ranging from the traditional beater spreaders (horizontal spinning disks) up to aggressive attachments with chopping knives that can be adjusted to conditions.

“Remember to adjust these systems to the situation,” says Kelly Kravig of Case IH. “Both the chop length and the distribution pattern can be altered.”

For small grains and soybeans, operate choppers at a high speed, recommends Kevin Cobb of Massey Ferguson. In corn, you end up running at a slow speed. “By not switching to slow speed in corn, the impact of cobs can start to create more damage,” Cobb says. 

2. Maintain choppers

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Here's a 5-step guide to combine chopper maintenance and repair.

Residue-management systems (also known as the combine chopper) are a great tool for sizing and spreading residue evenly across a field. But they are a powerful accessory that demands attention, otherwise, “you can end up with a $7,000-plus repair in the form of buying a new chopper,” warns Earl Knuth of MachineryLink. “Balanced rotation is the key to smooth chopper operation and a long life.”

Knuth, who has seen unattended choppers self-destruct from vibration ending up being drug behind a combine, offers the following five-point inspection plan to head off disaster.

  1. Examine drive belts for separation, wear, and dilapidation. “Considering the job they perform in transmitting power, the entire length of belt should be scrutinized,” Knuth says. In that regard, examine the belt's cover for separation, missing chucks, and burned streaks, grooves, and glazing. Detecting any of these problems requires that the belt be replaced. These conditions can also indicate a problem with misadjustment (of an idler or tensioning pulley) or an impending parts failure (such as a bearing going bad). “Worn or damaged belts set up vibration in the chopper. And vibration is the worst enemy of this attachment,” Knuth warns.
  2. Examine the hinge (pivoting) point where the chopper attaches to the combine. Look for cracking around the hinge point. Also, check that neither the mounting bolt holes nor the bolts are worn. Cracking and wear indicate excessive vibration, Knuth says. “Also look behind the rotor bearing for cracks in the sheet metal.”
  3. Take the belt off the rotor and turn it over by hand. Position a helper at the other end of the rotor shaft in this effort. “Doing so provides you a great opportunity to listen and feel (by placing a hand on the bearing) for any grinding noise,” Knuth says. “Grinding noise indicates that the bearing needs to be replaced. The speed at which these choppers rotate makes it very critical that you check their bearings.”
  4. Inspect the chopper's knives – both those on the rotor and stationary knives – for wear and damage. “Anything that damages those knives, taking a nick out of them, will throw the chopper out of balance. And balanced operation is everything with chopper operation,” Knuth says. “Remember, a chopper is throwing a lot of metal around at a high rate of speed.” Replace all worn and damaged knives and do so in sets. “Knives work in opposing pairs, and both knives must be replaced even if only one of them is damaged,” Knuth says. “New sets of knives come with installation instructions. Always follow manufacturer instructions to a tee.” Sharp knives (those that rotate and those that are fixed) cut better and require far less power to operate, says Jeff Gray with Claas of America.
  5. Inspect the chopper's distribution vanes. “Often overlooked, these vanes can become damaged from impact,” Knuth says. “Cracks in these vanes, as well as surrounding sheet metal, catch and keep crop trash, which compromises even residue distribution.” Sheet metal cracks can also indicate excessive operating vibration from a bad bearing or a damaged knife.

3. Consider a head that processes residue

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Accelerate cornstalk decomposition with the right head.

The front line for battling residue stands at attention in front of the combine with the corn head. Sensing farmers' needs to process stalks during harvest, manufacturers now offer a wide range of head options capable of chopping, crimping, crushing, and lacerating stalks as they go through the corn head.

“The more those stalks are chopped, lacerated, or crushed, the more access soil microorganisms have to stalk material,” says Steven Butzen of Pioneer Hi-Bred. “Which type of these stalk-aggressive heads you choose depends somewhat on your tillage system.”

Phil Needham of Needham Ag Technology defines a chopping head as one that employs horizontally spinning blades under the head (shown in the upper left image) to chop stalks as they go through. The purpose of the blades is to reduce the length of material at harvest, which accelerates decomposition.

A crimping head (shown in the illustration at far left) or a shredding head (shown near left) generally operates vertically and employs knife rollers that crimp, lacerate, or grind up the stalk as they are pulled through the head (depending on the design).

“Crimping or shredding heads generally chop the residue into shorter pieces or crimp the stem to get multiple entry points for microbes to accelerate decomposition,” Needham says.

“Imagine a 4-foot cornstalk pulled through two counter-rotating rollers with knives. They will generally shred the residue, or at least kink it and damage the stalk to the point where residue will deteriorate faster. You accelerate breakdown if you've got multiple entry sites for moisture and microbes,” he says.

The head system you choose will depend somewhat on your needs, of course. For example, you may opt for a horizontally or vertically chopping head if you plan to follow behind the combine with some form of fall tillage. Heads that crimp or crush stalks may work well in no-till or spring minimum-till fields when you want to leave stalks standing during the winter.

The power required for all aggressive head types is greater than a standard corn head, Needham notes.

“For certain, you don't lack alternatives in a processing head,” he says. “Generally, the amount of damage to the residue will be related to the power consumption and fuel usage of the combine.”

Regardless of the type of corn head you put to work, University of Nebraska agricultural engineer Paul Jasa says if a head is doing its proper job, the only things coming out of the back of a combine should be cobs and husks.

“If more than that is seen, the corn head itself needs attention,” he says.

4. Leave stalks upright for no-till

The challenge of heavy residue cover, particularly in corn-after-corn, is keenly felt by no-tillers trying to blaze a trail through last year's stalks. Almost universally, the experts urge no-till farmers to leave stalks standing tall during harvest (by increasing the operating height of the corn head) and to not chop stalks during (with a chopping corn head) or after harvest (using a stalk shredder). “If I was in corn-on-corn no-till and planting between rows, then I'm not going to chop down and flatten that residue,” says Steven Butzen of Pioneer Hi-Bred. “I'm better off leaving 18 inches of stalk to minimize how much trash ends up in next year's planting strip. If I was going to some minimum tillage, that becomes a different equation.”

Ag engineer Paul Jasa agrees. “In the early days of zero tillage, I liked to run the corn head about 6 to 8 inches off the ground to get all the residue processed through the snapping rolls,” he says. “Now I prefer to leave stalks 18 to 24 inches high. This provides for more uniform residue cover. Also, standing residue catches more snow in the winter, keeps the wind from moving residue around the field, and helps warm up the soil in the spring.”

Stalk shredding with a rotary or flail chopper, on the other hand, can leave a mat of residue that may keep no-till soil surfaces wetter and colder the next spring, says Richard Wolkowski, University of Wisconsin agronomist. “I'm definitely not a fan of chopping stalks after harvest when planting no-till,” he says. “Actually, I think that chopping in a no-till system might make matters worse.”

With no-till, you must be a stickler for spreading residue as evenly as possible across the full width of a combine. “Avoid, at all costs, leaving a trail of chaff or residue directly behind the combine,” Wolkowski warns. “You may have to invest in a residue-management system that distributes trash more evenly behind the combine, if you don't already have such an attachment.”

Run off to the side of the row. “Planting 4 to 5 inches off to the side avoids last year's old root stumps,” Jasa says. “Simply line up a tractor's tires to run next to last year's row. This way you plant 4 to 5 inches off the old row and avoid tire stubble damage.”

5. Fine-tune tillage

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Turning to tillage to tame residue requires keeping soil-engaging essentials sharp, regardless of differing implements and when you till.

“You can handle a lot of residue with sharp disks and coulters, keeping the implement level and then tilling at an angle to the rows,” says Richard Wolkowski, University of Wisconsin agronomist.

Sharp disks are very efficient at dicing stalks rather than hairpinning them into the soil. Implements leveled both front to back and side to side are far less apt to bury part of the implement's gangs in the soil while the other end or side of the implement runs lightly across the field. And tilling sideways to rows presents stalks to coulters or disks at an angle for more effective sizing of trash.

Those tips aside, the range of tillage tools available has grown in recent years with the advent of vertical tillage implements.

“When used in the fall, vertical tillage tools are designed to size residue, incorporate some of it with soil, thereby, accelerating microbial action and hastening decomposition over the winter,” says Phil Needham of Needham Ag Technologies. “They are designed not to bury residue but, rather, to hasten its decomposition while on the surface of the field. There is a place for these machines, depending on your tillage plans.”

Traditional tillage tools – such as disks or coulter-chisel combinations – are also effective in slicing up residue but also bury part of the residue in the soil after a single pass.

“Which implement you go with really depends on your system,” Wolkowski says. “If you're having trouble just getting primary tillage done (due to abundant residue), I suggest that maybe you look at the implement you have and possibly make a change.”

For example, if you opt to add a chopping or crushing corn head to your combine, then the need for the tillage implement to size stalks has been reduced. Straight corn heads may require implements with more cutting coulters or disks spaced closer together.

“It's tough to provide a one-answer-fits-all solution, as even crop rotation has an impact on tillage-tool selection,” Wolkowski says.

He does note that based on two years of recent field tests, chopping or shredding stalks (using a flail chopper in his trials) by itself reduces residue cover by a third. Following shredding with fall chisel tillage reduces surface residue from 61% down to 41%. Subsequent secondary tillage the following spring may reduce surface residue below 30% in the chopped fields.

“There are a number of conclusions you can draw from this research,” he says. “But we also found that chopping did not affect early-season soil temperature, seed-emergence rate, final stand, early-season plant height, or corn yield.”

6. Minimize tire damage

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Stubble can shred rubber.

The bite that stalks and stubble take out of tires can be minimized by employing a few precautions starting with letting cornstalks stand taller during harvest.

Paul Jasa suggests leaving stalks standing taller than 1 foot after harvest (he prefers 18 to 24 inches).

“I never have tire problems at that length,” the University of Nebraska ag engineer says. “That's because when I hit a tall-standing stalk with a tire, it will lean over without puncturing the tire.” Cutting cornstalks 6 inches or shorter leaves a sharp stump behind that can attack tires, he warns.

Jasa and representatives from the tire industry are big proponents of using stubble shoes or similar devices on combine heads or in front of tractors to knock stubble over in front of tires.

Jeff Vasichek of Titan Goodyear says during tillage it's better to run with the grain of the stalks as they were harvested. “This way, stalks are leaning over and away from the tractor and are less likely to be angled into the tire,” he says.

Wayne Birkenholz of Firestone Tire recommends not installing new tires on tractors running in aggressive stubble. As tires age, they harden, and that lessens damage to the rubber.

Be sure to maintain proper tire inflation. Underinflated tires are more susceptible to stalk damage.

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