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Cut corn head casualties

Thanks to more accurate loss monitors, remote combine adjustments, and vigilant farmers, grain shooting out the back of combines has been slashed to miniscule amounts of 1% or less.

Too bad the same can't be said for corn heads. Increasing yields, tougher stalks, and more resilient shanks are challenging row heads as never before. As a result, header losses appear to be increasing, depending on harvest conditions each fall.

“Today's heads are certainly better than those of the past, thanks to improvements such as lower profile snouts, remote adjustable stripper plates, and variable-speed drives,” says Kevin Bein of Gleaner. “But, you can't assume a good header is taking in all the crop. You need to get out of the cab and look under the combine to determine header losses.”

These losses take two forms in shelled grain (most often due to butt shelling) and whole ears. Combined, they can claim 5 bushels or more per acre. And with corn at $6 or more per bushel, such losses take a big bite out of bottom lines.

For example, finding two kernels per square foot or a single ear in a row behind a combine represents a 1-bushel-per-acre loss. “In the latter case, that's the average from the loss of one modest-size ear dropping down every 50 feet of row,” says ag engineer consultant Graeme Quick.

Quick led a field research effort at Iowa State University funded by Successful Farming magazine, which purposely misadjusted combines to gauge the affects of operator error. That work, combined with field surveys by Quick, revealed that deck plate misadjustment on corn heads is a particularly troublesome problem.

Results of that research are shown in the table below.


“Certainly no one would operate a corn head with a 1⅔-inch or wider deck plate settings in an average corn crop,” Quick says. “We went to extremes in adjustments to see what happens to losses.”

Losses accelerate

The ideal setting for the corn being harvested in Quick's research was 1 inch. What he discovered was being off by just ⅜ inch (with deck plates set at 1⅜ inches) reduced the amount of crop being harvested by as much as 26 bushels an acre. That represents a $156-per-acre loss with $6 corn.

Quick acknowledges that a great many corn heads in the field today have hydraulically or electronically adjustable deck plates that allow farmers to readily adjust gaps to changing stalk sizes (which can vary by variety). But he warns that remotely adjustable plates can be plagued by spacing problems due, particularly, to maintenance challenges.

“Over time, plates can seize (from rust) and become inoperable,” he warns. “That's why it is crucial that prior to harvest you get out of the cab and measure plate gaps to confirm they are consistent with the setting in the cab.”

Quick has found heads with adjustable plates operating with gaps that vary as much as ½ inch between rows.

When it comes to adjusting deck plates during the season, be sure to set them narrow enough to keep ears from butt shelling, but don't set them so wide as to allow small ears to fall through. Another consequence of too narrow a spacing is that this setting can result in excessive trash coming into the head.

Finally, set plates so they are always tapered from the front to the back. As a rule of thumb, the bottom gap should be set ⅛ inch wider than the top opening. While you are making that adjustment, check to see that the gap between the snapping rolls is the same as the plates.


Other head adjustments are listed below.

1. Set trash knives on corn heads close to the snapping rolls to prevent weeds and stalk material from wrapping on the rolls.

2. Match the gathering chain movement to the forward speed of the combine. If chain speed is too fast, stalks may be pulled out of the ground and broken, which results in ear losses. If the combine is traveling too fast for the chains, stalks will be pushed forward and ears will be stripped off.

3. In good field conditions, maintain a speed of 2½ to 3 mph. If corn is badly lodged, slow down and let the snouts float on the ground to lift crop.

4. Adjust gathering chains so their flights are opposite each other and extend about ¼ inch beyond the snapping bars.

5. Adjust snouts so their tips are as low to the ground as possible, if not just touching the soil. The angle of the snout relative to the ground should be at a minimum.

6. The opening between deck plates should be narrow enough to keep ears from butt shelling, but not so wide to allow small ears to fall through. A typical starting point for adjustment is to set plates at 1⅛ inches recommended by most manufacturers. Ideally, the plate openings should be adjusted on-the-go within a field to suit that crop. Settings need to be reassessed when changing varieties and fields.

7. Clear the feeder house slats 1 inch above the floor of the front of the feeder house. Deviate from that basic setting to suit different crop conditions.

8. Clear the flighting on a corn head's auger from the stripper bar so that crop or stringy material is not carried over and around the auger. For heavy crop conditions, clearance can be brought up and forward for greater capacity and less carryover by the auger.

9. Adjust snapping roll speed and spacing so the rolls snap ears off at a position about one half to two thirds of the way up the deck plates. Snapping bars should be spaced narrower in front than in back to prevent ears from wedging and shelling out (butt shelling).

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