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Harvested yields of soybeans in many North Carolina fields can easily be increased by 5 to 10 percent just by leaving fewer beans in the field when combining. Studies have shown that field losses average about 10 percent of yield, but run as high as 15 to 20 percent in many cases. A machine harvesting loss of only 3 to 4 percent (114 to 112 bu/a in 40 bushel beans) is practical to achieve with carefully operated modern equipment. Careful combining costs nothing extra, so the additional beans harvested go directly into the net profit column.

Unless you know how much you are losing and from what part of the machine the loss is coming, you don't know how to make corrections. It is essential to measure losses and pinpoint their source to see where machine adjustments are needed. Always recheck losses after making adjustments to see if they had the desired effect. Once you learn the procedure, a loss check can be made in just a few minutes.

Types of Losses

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Soybean field losses fall into one of the following categories:

Preharvest Loss. Loose beans or beans in detached pods which are on the ground prior to harvesting.

Gathering Unit Loss. All beans which are attached to plants at harvest, but which never get into the combine. Most harvesting losses are in this category. There are four types of gathering unit losses:

  • Shatter loss - loose beans and detached pods resulting from harvesting,
  • Stubble loss - beans remaining in pods attached to stubble,
  • Lodged stalk loss - beans remaining in pods attached to stalks which were not cut, and
  • Loose stalk loss - beans remaining in pods attached to stalks which were cut but not delivered to the threshing unit.

Cylinder loss. Beans which pass through the combine but remain in the pod.

Separation loss. Threshed beans which go out of the combine with the trash.

Procedure for Checking Losses

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Estimates of the bushels per acre of soybeans lost are based on the number of beans per square foot left in the field after harvesting. About four average-size beans per square foot are equivalent to one bushel per acre. It may require up to 10 very small beans or only two very large beans per square foot to equal one bushel per acre.

Bean counts are made in a 10-square-foot area. It is convenient to mark the area with a collapsible rectangular frame made from four stiff wire pegs and string, which can be rolled up and carried on the combine. Width of the rectangle should equal the swath width of the combine header. The length needed to enclose 10 square feet can be determined from Table 1.

  1. Determine the total field loss. Stop the combine (do not clear), well in from the end of the field, where the crop is typical of the whole field. Disengage the gathering unit and back up about 15 feet. Place the rectangular frame across the harvested swath at the rear of the machine. Count all beans within the frame area and record in column A, line 1 of Table 2. Divide by 40 (in average-size beans) to get bu/a of preharvest plus harvesting loss and record in column B, line 1.

    If the total field loss is not more than 3 percent of yield (1.2 bu/a in 40 bu/a beans), continue harvesting. If total loss exceeds 3 percent, follow steps 2 through 5 to see where the losses occur and make adjustments to reduce them.
  2. Determine the preharvest loss. Place the rectangular frame in standing soybeans in front of the combine, and count all beans lying loose on the ground within the frame, both in and out of pods. Record the total count in column A, line 2 of Table 2. Divide by 40 to get bu/a, and enter in column B, line 2.
  3. Determine the overall machine loss. Subtract the preharvest loss (line 2) from the total field loss (line 1) in columns A and B, respectively, of Table 2. If the machine loss is not more than about 3 percent of yield (1.2 bu/a in 40 bu/a beans), continue harvesting. If more, proceed with the remainder of the loss analysis and make adjustments to reduce losses where needed.
  4. Determine the gathering unit losses. Place the frame across the harvested swath between the combine header and the standing beans. Make counts as follows:
    1. Shatter loss. Count all loose beans and beans in detached pods lying on the ground. Subtract preharvest loss (column A, line 2) and record remainder in column A, line 4a. Divide by 40 and enter bu/a in column B, line 4a.
    2. Stubble loss. Count beans in pods attached to stubble, and enter in column A, line 4b. Divide by 40 and enter bu/a in column B, line 4b.
    3. Lodged stalk loss. Count beans in pods attached to stalks which were not cut, and enter in column A, line 4c. Divide by 40 and enter bu/a in column B, line 4c.
    4. Loose stalk loss. Count beans in pods attached to loose stalks or portions of stalks which were cut but not gathered by the header, and enter in column A, line 4d. Divide by 40 and enter bu/a in column B, line 4d.

      Determine total gathering unit losses by adding the number of beans representing shatter, stubble, lodged and loose stalk loss (column A, lines 4a-4d). Enter total in column A, line 4. Divide by 40 and enter bu/a (total gathering unit loss) in column B, line 4.
  5. Determine cylinder and separating losses. Subtract gathering unit loss (column B, line 4) from overall machine loss (column B, line 3), and record in column B, line 5.

Examine the various types of gathering unit losses, and the cylinder and separating losses to see where adjustments should be made. Comparison with the "acceptable" losses in column C, lines 4a-4d should be helpful in identifying the problem source. If your yield is much different from 40 bu/a, these "acceptable" bushel-per-acre losses should be adjusted accordingly. Make only one change in combine adjustment (i.e., reel speed, reel height, ground speed, cutter-bar height, cylinder speed, concave clearance, etc.) at a time, and recheck losses to see if the change improved performance. If not, go back to the original setting and try another approach, rechecking losses after each change. Only with this systematic approach can you isolate and correct the cause of excessive harvesting losses.

Operational Guidelines

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Typically more than 75 percent of soybean machine harvesting losses are gathering losses, so greatest attention should be given to proper header adjustment and operation. Some of the more important things to remember are:

  1. Keep ground speed to 3 mph or less. Long stubble, uneven cutting height and shatter losses due to knife stripping are indications that ground speed is too fast.
  2. Operate cutterbar as close to the ground as possible at all times. A floating flexible cutterbar with automatic header height control is virtually essential for low loss levels.
  3. Keep knife sections sharp, and make sure guards, wear plates and hold- down clips are in good condition and properly adjusted. Narrow-section knives reduce shatter and may permit slightly higher ground speeds.
  4. Operate reel about 25 percent faster than ground speed. Position reel axis 6 to 12 inches ahead of cutterbar. Bats should enter crop only enough to gain control.
  5. Complete harvest as quickly as possible after beans first reach 15 percent moisture. When beans reach 13 percent moisture or less, take advantage of damp pod conditions brought on by dew, light rain or high humidity to reduce shattering.
  6. Operate the cylinder at the slowest speed which will give complete threshing to reduce splitting. Check and adjust if necessary as conditions change from damp to dry.
  7. Measure losses when field and crop conditions, varieties or machine settings change.

Table 1. Dimensions for rectangular 10-square-foot plot.

Swath width (ft) Distance along row to enclose 10 square feet (inches)
8 15.0
10 12.0
12 10.0
13 9.25
14 8.6
15 8.0
16 7.5
18 6.7
20 6.0

Table 2. Soybean field losses.
Step Type of Loss Frame location or How Calculated Column A Column B Column C
in 10 sq-ft area;
Max "acceptable" loss
in 40 bu/a
1. Total Behind combine 1.2
2. Preharvest In standing beans 0.1
3. Machine Total minus preharvest 1.2
4. Gathering unit Between header and standing beans 1.1
a. shatter All loose beans minus preharvest loss 0.4
b. stubble All beans in pods still attached in stubble 0.3
c. lodged stalk All beans in pods still attached to lodged stalks 0.2
d. loose stalk All beans in pods still attached to loose stalks 0.2
5. Cylinder & separation Machine minus gathering unit loss 0.1
* Beans in 10-sq-ft area divided by 40, for average-size beans.


Professor and Extension Soybean Specialist
Crop and Soil Sciences
Extension Specialist
Biological and Agricultural Engineering

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Publication date: Nov. 22, 2017

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