Soybean Harvest

Pawel Wiatrak, Emerson Shipe, and Jason Norsworthy

When harvest is delayed due to bad weather, or when some varieties dry down to seed moisture levels below 11 percent, seed shattering may occur in the field or at the cutter bar at harvest. To reduce the potential for shattering losses, harvest should begin at seed moisture levels of 14 to 12 percent.

If storage bins have the capacity for drying with air blowers, harvesting at 16 percent is not out of the question. In fact, for most years in South Carolina those farmers who wait for ideal moisture around 12 percent often have difficulty in harvesting their entire crop without losses in yield and quality, either from shattering, lodging, or disease. Timely harvest is essential in obtaining maximum yield and a high quality crop. Significantly reduced yield and quality may be expected if harvest of maturity group IV is delayed due to unfavorable weather conditions.

Lodging, plants falling over, can occur at any time after first bloom, and is usually more of a problem with broadcast or drilled plantings. Early lodging can reduce yields by interfering with pod set and pod fill, or by encouraging more pod and stem disease problems. Late lodging, such as after a storm with heavy winds, can reduce yields and seed quality because of harvest difficulties and/or improper drying down of the crop.

Tall, late-maturing varieties, soybean planted at higher than optimum seeding rates, or soybeans planted in highly fertile bottomland have a higher risk of losses due to lodging. Farmers who anticipate a problem with lodging should select varieties with strong upright stalks or main stems (usually the shorter varieties in Groups V and VI). Additionally, using the proper seeding rate for the row spacing will assist in reducing losses from lodging (see the Planting Considerations section). If excellent growing conditions are expected, seeding rates can further be reduced to ensure crop stand ability.

To estimate the soybean yield prior to harvest (calculate loss or storage needs, insurance purposes, etc):

  • Count the number of plants from 10 randomly selected rows to get the average plant number. For example, count plants in 14'6" long rows for 36 inch wide rows or 13'9" long rows for 38 inch row spacing (1/1000 of the acre) (Table 1). Calculate the average and multiply by 1000 (this is your plant population per acre).
  • Count the number of pods per plant from 10 randomly selected plants and calculate the average.
  • Multiply the plant population per acre by average number pods per plant to get the number of pods per acre.
  • Multiply the number of pods per acre by 2.5 (avg. number of seeds per pod or use your own number) to get the number of seeds per acre.
  • Divide the number of seeds per acre by 2500 (or known number of seeds per pound for the variety) to get weight in pounds per acre.
  • Divide the weight in pounds per acre by 60 to get yield in Bu/acre.

Table 1. Row spacing and row length for 1/1,000 acre.

Row spacing (inches)

Row length (1/1,000 acre)

15

34 ft. 10 inches

20

26 ft. 2 inches

22

23 ft. 9 inches

28

18 ft. 8 inches

30

17 ft. 5 inches

36

14 ft. 6 inches

38

13 ft. 9 inches

40

13 ft. 1 inch