Combine Settings for Drought

August 9, 2012
ICM News

By Mark Hanna, Department of Agricultural and Biosystems Engineering

Hot mid-summer field conditions are affecting upcoming harvest. Although soybeans are still developing, corn ear diameter has been established in most fields. Smaller ear diameter and, in some fields, weaker stalks at the base of the corn plant and at the ear shank will affect harvest operations. 

 General harvesting

Crop conditions vary across regions, but also within fields in the same farming operation. Harvest won't be business as usual. Pre-scouting fields and approaching harvest with the right attitude is an important first step. We know that faster combine travel speed helps load the combine and improve grain quality; however, with weak and/or lodged stalks and stems it may be necessary to travel slower to ensure the crop feeds into the combine as easily as possible. Finding the correct travel speed to balance machine field losses (reference PM 574, Profitable Corn Harvesting, to check field losses) with crop quality requires checking both losses behind the combine and grain quality in the tank. Be sure to check before harvest with your crop insurer if losses will be claimed. Warmer temperatures associated with an early harvest and dry field conditions increase fire potential. Review your combine and field fire prevention plans.


Ear sizes vary in fields. In many cases, ear diameter (cob and grain) is smaller than normal. On the cornhead, the gap between snapping plates above the stalk rolls should be adjusted so that the ear butt is held on the plates above the rolls but with is enough room for stalks to be pulled through without wedging. A gap of 1.25 inches used in normal years will likely need to be narrowed closer to just over an inch to avoid butt shelling of smaller diameter ears. 

Smaller diameter stalks may be more easily pulled between narrowed snapping plates, but a weakened stalk base makes corn susceptible to lodging by late-season winds. Similarly, weakened ear shanks in some fields may cause ear droop, making it advantageous to scout individual fields for early harvest. Significant amounts of lodged corn may require slower travel speed and/or the use of a reel, cones or divider modifications on the corn head. 

Concave clearance should be adjusted for ear size and material flow. Smaller diameter ears and less plant material suggest narrower concave clearance than normal. Don't use faster rotor or cylinder speed than necessary for adequate threshing. Check the amount of seed coat cracking to fine-tune concave clearance and rotor speed. Smaller kernel sizes may require smaller than normal sieve openings in the cleaning shoe. Be careful not to adjust so small that significant amounts of grain are recirculated in the tailings return. Air drag is slightly greater on smaller kernels but, unless test weight is low, fan speed should be similar to normal. Kernel size may be larger on ears with significantly fewer kernels requiring larger sieve openings. 


Crop and field conditions still have the potential to change before harvest. Plant heights, however, appear shorter in a number of fields. Some grain platforms allow the cross-auger position to be moved forward. This may be considered to help pull shorter plants away from the cutterbar and into the feederhouse. The reel can be adjusted downward but be careful that reel fingers are not clipped by the cutterbar when it flexes upward to its highest position. 

If biomass amounts are smaller, concave clearance may need to be decreased to allow adequate traction to pull material though the threshing area. Check the grain tank for splits and seed coat cracks. Use only enough rotor speed and only narrow enough concave clearance as required for grain quality and throughput. Low yield areas in some fields may keep plant stems green when beans and pods are mature and ready for combine harvest. These conditions require more attention to adjust aggressiveness of threshing (speed, clearance) for adequate threshing and throughput without causing green discoloration to soybeans. 

Smaller soybeans require slightly narrower sieve openings in the cleaning shoe. Fan speed may be reduced if soybeans are blown out the back. Extremely small soybeans may be brittle during threshing and challenging to clean. 


Don't assume crop conditions. Inspect fields for variability. Schedule field harvest based on factors of yield and preharvest loss potential, as well as optimizing adjustments required on the combine. Make it a safe harvest. Unscheduled downtime due to accident or fire is more costly than a few extra bushels of preharvest loss.

Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Hanna can be reached at or (515) 294-0468.

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