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Drought a challenge to soybean harvest

Reducing harvest losses is a simple and effective way to increase soybean yields and profitability. Losses of 7.5% are common, but could be much higher this fall due to the drought and heavy spider mite infestations.

The drought reduced overall plant height and the height of the lowest pods on the plants. Both conditions increase the potential for gathering losses at the combine head. The pods will also be more brittle and prone to shatter losses in fields that have been stressed by spider mites.

With careful maintenance and operation, harvest losses can be maintained at 3%. Reducing harvest losses from 7.5% to 3% in a 45-bushel-per-acre soybean crop will increase the marketable yield by 2 bushels per acre. With market prices projected to average nearly $16 per bushel for the marketing year, this translates to $32 per acre of additional income.

Key Points

• The drought reduced height of overall plant and the lowest pods on the plant.

• Shatter losses shown to greatly increase when seed moisture falls below 11%.

• Nearly 80% of harvest losses occur while cutting, gathering plants into the combine.


Properly timing your harvest operations is critical in reducing harvest losses. Harvest can begin anytime after the beans have initially dried to 14% to 15% moisture. This will occur five to 10 days after 95% of the pods have reached their mature color under good, drying conditions.

Harvest as much of your crop as possible before the moisture level falls below 12% to reduce splits and cracked seed coats. Shatter losses have been shown to increase significantly when seed moisture falls below 11% and when mature beans undergo multiple wetting and drying cycles.

Before harvest operations begin, inspect and repair the cutting parts on the header. Make sure that all knife sections are sharp and tight. Check the hold-down clips to ensure that they hold the knife within 1/32 of an inch of the guards. Adjust the wear plates to the point that they lightly touch the back of the knife.

Equipment adjustment

Information from the University of Arkansas shows that a skilled combine operator can reduce harvest losses significantly when compared to an inexperienced operator or one who is trying to hurry or cut corners. Combine operators should understand how losses occur and how to make the proper adjustments.

Nearly 80% of harvest losses occur while cutting and gathering the plants into the combine. Most of these are due to shattering. The following recommendations will reduce gathering losses:

Maintain ground speed at 3 mph or less. Higher speeds are reported to be possible with a draper head or when air is added to the head. Pods stripped from the stalks and uneven stubble are signs that the travel speed is too fast.

Set the speed of the reel to run 25% faster than groundspeed. For a reel with a 42-inch diameter, this is 10 rpm/mph.

If the beans are lodged, increase the reel speed up to 50% faster than the ground speed (11 rpm/mph).

Position the reel axle 6 to 12 inches ahead of the cutter bar. Ideally, the reel should leave the beans just as they are being cut. Set the height of the reel just low enough to control the beans (generally the top third of the plants). In lodged conditions, operate the reel as low as necessary to pick up the plants.

Measuring gathering losses after each adjustment is the best way to verify your progress. Losses can also occur once the beans have entered the combine. However, the combination of these losses typically accounts for only 1% of the total harvest losses.

For more information, visit www.msue.msu.edu. To contact an expert, visit expert.msue.msu.edu, or call 888-678-3464.

Staton writes for MSU Extension

This article published in the October, 2012 edition of MICHIGAN FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.