How To Estimate Grain Harvest Losses

Studies have shown that losses off the combine can run as high as 20%, even with a properly adjusted machine when it is overloaded. A reasonable loss is considered to be 3% of the total crop or less. Total harvest losses are seldom if ever zero.

Usually over 60% of the grain left in the field is due to shattering of the crop and grain lost in getting it cut and into the combine header.  Once the crop is in the combine, loss is very low with properly adjusted and operated equipment.

To keep harvest loss low, determine how much grain is being left in the field. A simple, accurate method to estimate losses requires the use of a one-foot square frame.  Pick several typical areas in the field after the combine has passed and follow these steps.

1. Count the kernels left directly behind the rear of the combine.  Count several separate square foot areas (A- Figure 1).

Figure 1: Sampling Locations to Estimate Combine Yield Losses

2. Count the kernels already in the field due to shatter and cutter bar loss (B- Figure 1).

3. Subtract (B) from (A).

4. Divide the results of  Step 3 by the ratio of:
Width of windrower/header width (ft)
Width of combine (ft)

5. Divide the result of Step 4 by the number of kernels for the particular crop from the Table 1 (above right) for one bushel per acre loss.  This is the approximate machinery loss in bushels per acre.

6. To find total loss, add the count in (B) to the result in Step 4.  This gives the total seed count from shatter, cutter bar and machine loss.

7. Divide the total seed count of Step 6 by the number of kernels for the particular crop for one bushel per acre loss (Table 1).  This will give the approximate total loss in bushels per acre.

Table 1: Number of kernels per square foot to equal one bushel per acre loss. Crop Number of Kernels / ft2 HRS Wheat 20 Durum 16 Barley 14 Oats 10 Source: University of Minnesota Extension Service

8. For a percentage loss, divide the loss in Step 7 (loss in bushels per acre) by the total yield (harvest yield plus loss) in bushels per acre for the field.