September 5, 2017

By Mark Hanna
Corn and soybean crops are quite variable across Iowa as the 2017 harvest season approaches. Spotty rainfall, sandy or clay soil spots, temperature extremes and storms have resulted in varying sizes of corn ears and bean pods.
This variability exists among fields across Iowa — and in some cases within fields or even within individual rows. Such variations put a premium on proper combine adjustment this fall.
Proper adjustment can only be accomplished by taking time to measure and observe grain loss and quality. Combine grain losses can be held to 1 bushel per acre or less if the crop is standing reasonably well. One bushel loss equals two corn kernels or four soybeans per square foot on the ground. Grain quality is evaluated by inspecting harvested grain in the tank, looking for splits in soybeans, and cracked or damaged seed coats in corn or soybeans.
Measuring losses
Losses occurring at the head can be separated from losses of the entire combine by stopping the combine and backing up several feet to look for losses on the ground traversed by the head, but not the rear of the combine.
How to measure losses can be found in two Iowa State University publications: PM 574, Profitable Corn Harvesting, and PM 573, Profitable Soybean Harvesting. Field studies show 90% of soybean loss and 60% of corn loss typically occur at the head with proper threshing and separating adjustments.
Header adjustments needed
For corn, ear diameters in some fields are smaller than normal this year. The gap between deck plates above snapping rolls (1.25 inches in normal conditions) should be narrow enough to avoid shelling kernels on the ear, yet wide enough for stalks to be pulled through without wedging. Stalk roll speed should be matched to ground speed. Ear savers (at the bottom of stalk rolls) should be in good condition to keep ears from bouncing from the head.
For soybeans, research identifies the cutterbar as the most responsible for soybean losses, but reel speed and position, and cross-auger operation, can also affect losses. Ensure that cutterbar sections are sharp, in register with guard positions and held firmly against the guard with hold-down clips. The reel centerline is normally about 8 to 12 inches in front of the cutterbar, with height adjusted so that reel finger tips are no closer than about 2 inches to the flexible cutterbar when at its highest position.
Reel speed index (ratio of peripheral reel speed to combine travel speed) is normally about 1.25 (25% faster reel than ground speed) but may be up to 2.0 (twice as fast) if the crop is severely lodged. If plants are short, the cross-auger position on some heads can be moved forward to help pull plants into the feeder-house. The position of the front idler drum of most feeder-house chains is adjustable and should be in the lower position for soybeans (particularly if the crop is short) to help pull in crop.
Check rotor, concave
Before harvest, check the condition of your combine’s rotor or cylinder, and concave. Level and calibrate the rotor position according to the manual, or re-zero the concave to the rotor. Start at the lower end of suggested rotor speeds, using only enough speed to minimize threshing loss. Clearance of the concave with the rotor may be narrower than normal for smaller corn ears, or shorter or fewer soybean plants.
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 the aggressiveness of threshing (speed, clearance) for adequate threshing and throughput without causing green discoloration to soybeans. Keeping the thresher loaded limits grain damage, but it may be more difficult in lighter crops where excessive travel speed can increase combine grain loss.
Inspect combine’s cleaning shoe
Sieve openings may need to be smaller if corn kernels or soybeans are smaller, but this may increase the amount of grain going to the tailings return and increase grain damage as it passes again through the rotor or concave area. Kernel size can also be larger on ears with significantly fewer kernels, requiring larger sieve openings.
Adequate airflow is necessary for good separation and cleaning, so start near the upper end of fan speed and reduce speed only if necessary to limit lighter-weight grain blowing out the rear of the combine.
Think safety
Review safety procedures and train everyone involved with harvest. Fire is always a potential with dry, combustible plant material and combine heat sources. Also, the lighting on your equipment and the marking should be checked to ensure safety when moving the machines between fields. During the 2017 harvest season, 3 billion bushels are expected to be removed from Iowa fields.
Overall, don’t assume crop conditions are whatever you think they are. Get out into the fields. Do a preharvest inspection of fields for variability. Be sure to check before harvest with your crop insurer if yield or crop losses will be claimed.
Schedule the harvest of your fields based on factors of drydown and preharvest loss potential, as well as optimizing adjustments required on the combine. Harvest your fields that contain invasive weeds last or clean out the combine between fields.
Develop the right attitude and make it a safe harvest. Unscheduled downtime due to accidents or fire is more costly than taking short breaks to recharge and rest.
Hanna is an Iowa State University Extension ag engineer. Contact him at [email protected].
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