Corn Harvest - Minimizing Foreign Material in the Combine’s Grain Tank

Matthew Digman, Assistant Professor and Machinery Systems Extension Specialist, UW - Madison

Reports from the field are that corn grain is being docked and in some cases rejected due to large amounts of broken corn and foreign material (BCFM). The U.S. standard for No. 2 yellow corn is less than 3% BCFM. Foreign material and grain fines rob grain bin capacity because they occupy space that was intended for grain. Additionally, airflow can be restricted by pockets of foreign material and fines, causing hot spots, damaging grain and possibly leading to fire.  Here are a couple of tips to follow if you are finding a large amount of foreign material in your clean grain tank.

Ground Speed

Be sure to select a ground speed that does not overload your machine as the engine must be able to maintain its rated engine speed to keep separator and cleaning shoe at full speed. Adjust your speed with the hydrostatic transmission to maintain the engine near rated speed under varying crop conditions.
 

Header

The usual advice for minimizing trash input into the combine by operating the header as high as possible is even more critical in these wet conditions. Introducing tough, wet leaf and stalk material into the combine reduces its effectiveness to thresh, separate and clean the grain.
 

Concave Clearance

Your operator’s manual will specify clearances for your particular machine, but generally you’ll need to set your concave approximately to the diameter of a shelled cob. A properly adjusted concave will break up some cob, but excessive broken cob is an indicator that the concave is set too close to the cylinder or rotor. Too many broken cobs can lead to high levels of cob in the clean grain tank and/or can overwhelm the cleaning shoe.
 

Cylinder or Rotor Speed

After the concave is adjusted properly, adjust the cylinder or rotor speed to maximize threshing, but make sure you balance this adjustment with grain damage. If grain damage becomes excessive, slow the cylinder or rotor. Do not increase the concave clearance. Concave spacing has very little effect on grain damage in corn.

Cleaning Shoe

Always begin harvesting with the chaffer and sieve openings to the maximum specification for corn in your operator’s manual. Closing down the sieve will produce clean corn in the grain tank, but it will also increase tailings returned for rethreshing, which can increase grain damage.  If there is too much cob in the grain tank, first try increasing airflow, then close the top chaffer sieve a little and finally the lower shoe sieve a little. Wet crop residue will require higher air speed compared to a dry crop.

Monitoring Conditions

With the recent spell of favorable weather, crop conditions are begining to change. Be sure to check your grain tank throughout the day, when switching fields or varieties and as weather conditions change.

For more information on this year’s harvest please visit us at the new University of Wisconsin Cooperative Extension Team Grain website at http://fyi.uwex.edu/grain/.
 

References

Allis-Chalmers. 1980. Operator’s Manual: N5, N6 and N7. Milwaukee, WI
John Deere. 2003. Operator’s Manual: 9660 CTS. Moline, IL
John Deere. 2006. Recommendations for harvesting field corn, popcorn, soybeans peas and edible beans - STS Combines. Solution Number 44539. Moline, IL
John Deere. 2009. Operator’s Manual: 9570 STS. Moline, IL
New Holland. 2009. Operator’s Manual: CR9060, CR9070 and CR9080. New Holland, PA.
USDA-GIPSA. 1996. United States Standards for Corn. Washington, D.C.