Ronald T. Schuler, Extension Agricultural Engineer – University of Wisconsin
In a year of high energy costs, producers may want to delay corn and soybean harvest to reduce the energy cost of drying. When delaying the harvest field, pre-harvest losses will be greater resulting in a form of added costs which must be compared to the reduced drying cost.

The field losses occurring as pre-harvest losses are the result of lodging, ears dropping to the ground and wildlife. The level of these losses is dependent crop variety, weather conditions, and pest infestations. Each day the harvest is delayed the losses continue to rise.

In machinery management work, proper machine sizing involves the use of a timeliness factor, which assumes there is an optimum date for most field operations. For each day the operation misses this optimum date, a loss occurs. The American Society of Agricultural and Biological Engineers publishes machinery management data that includes the timeliness factor. It is an estimation of the yield loss in percent of the yield.

For harvesting shelled corn, the timeliness factor is 0.3 percent per day based on Iowa data. If corn combining is delayed 10 days, the predicted pre-harvest losses will be 3 percent. If the expected yield is 150 bushels per acre, then the predicted yield loss due to the ten-day delay is 4.5 bushels per acre. This is the only data available for shelled corn. For ear corn, a factor of 0.7 percent is listed for Illinois data for harvesting after October 26. These factors should have application in Wisconsin. This yield loss must be balanced with a reduced drying cost.

For harvesting soybeans, the timeliness factor ranges from 0.6 to 1.0 percent, depending the variety. This is for data obtained in Illinois. The ten day delay could range in losses from 6 to 10 percent and at a 45 bushel per acre yield the losses would be 2.7 to 4.5 bushels per acre. Considering the prices for corn and soybeans, it appears the harvest delay will be more costly with the soybeans.

The timeliness factor is used only as a rough estimate of the pre-harvest losses due a harvest delay. This assumes a constant rate of pre-harvest losses throughout the harvest season. Nonetheless it is sufficiently accurate to make some decisions, especially if a producer has a choice between delaying corn harvest or soybean harvest. Based on other field research for Indiana, Illinois, Iowa and Nebraska, the losses increased about 3.5 percent from September to October (0.11 percent per day) and about 10.0 percent from October to November (0.33 percent per day), which is close to the timeliness factor for corn harvest.

These values are based on good crop conditions: minimal pest infestation, minimal wind induced lodging and minimal wildlife problems. These adverse conditions will cause higher loss rates (percent per day) than used above. Following are some considerations for delayed harvest:

• If a field has infestations of corn borer and stalk rot, the risk of ears dropping and lodged corn are greater, then delayed harvest in not recommended.
• If the grain moistures are high, such as 24 percent, the drying costs are going to be high, usually directly proportional to moisture (Some estimates are 2 cents per point per bushel), then delayed harvest is recommended.
• When grain moistures are high, the corn dries faster suggesting a delayed harvest.
• Early November pre-harvest loss rates are nearly three times that in early October, then a delayed harvest into November is not recommended.

If a grower has a choice in the order of fields or areas of a field to harvest, some recommendations are:

• Harvest pest infested fields or areas first,
• Harvest drier fields or areas first, and
• Harvest areas with greater access to wildlife first, unless the grower has other reasons to feed the wildlife.

Some management of the fall harvest can help make the 2005 season more successful. As a result the impact of the high fuel costs and high field losses can be reduced.

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