Corn Harvesting Losses

Grain has been drying exceptionally well during 2015, so many growers will be in the thick of grain harvest this week. All your hard work during the growing season can quickly be lost if your combine is not set correctly during harvest season. Taking some time to thoroughly read and review detailed settings on your specific combine model can help you fine tune changing field conditions and weather.

Sources of grain losses can be broadly divided into pre-harvest losses, gathering losses and machine losses. Remember that every two kernels per square foot equals one bushel of loss per acre.

Pre-harvest Losses

Some losses can occur before the combine even reaches the field. Hybrids differ in their ability to retain grain on the plant due to maturity and ear droppage. One ear (3/4 pound each) in each 1/100 of an acre is equivalent to one bushel per acre. To determine 1/100 of an acre, take the normal 1/1,000 acre distance times ten. For example, in 30-inch rows, 1/1000 of an acre is 17 feet 5 inches; 1/100 acre would be that distance across ten rows. For each ear in that area, there is one bushel per acre loss.

Weather events and the ability of the farmer to be timely can also increase grain loss before the combine even gets to the field.

Gathering Losses

Gathering loss is grain that does not get into combine. Shatter losses caused by the header and can be determined by counting the number of ears and kernels under the header.  More than a half bushel per acre (or one kernel per square foot average) indicates adjustments would be appropriate. Grain can also be lost from stubble losses, stalk losses, and lodged plants.

Machine Losses

Machine loss is due to improper adjustment of threshing, separating and cleaning sections. Threshing loss is indicated by kernels attached to pieces of cob behind the combine. These were not shelled by the rotor or cylinder. Separating losses are additional loose kernels on the ground behind the combine. These were not shaken out of the cobs and husks and were lost over the back of the separator.

How to Measure Losses

Determine average loose kernel loss and cylinder/rotor loss

1. Every 2 kernels per square foot = 1 bushel per acre
2. Kernel still attached to cob = cylinder/rotor loss
3. Acceptable level = 1.2 to 3 kernels per square foot

Determine machine ear loss

1. Behind combine, gather all ears on 1/100 acre
2. In front of combine, determine pre-harvest ear loss in standing corn on 1/100 acre
3. Subtract pre-harvest ear loss from ear loss at the rear of machine
4. Each 3/4 pound ear = 1 bushel per acre
5. Each 1/2 pound ear = 2/3 bushel per acre
6. Acceptable level = 0 to 1.0 bushels per acre

Typical total field loss level = 0.6 to 2.5 bushels per acre. Goal is to limit total field loss to less than half a bushel per acre.

Further Reading

Wisconsin Corn Agronomy - Grain Harvesting