Soybean Harvest Considerations

Late planting this spring and cool temperatures lasting into the summer have resulted in short soybeans this year. Many fields are 10-25% shorter than average. This means that pods are lower to the ground and extra care will need to be taken to minimize harvest losses.

Seed Moisture

The best time to harvest soybeans is the first time they dry down to an acceptable moisture level (ideally 14%). Wet-dry cycles of mature beans will decrease quality and increase harvest losses. Seed diseases such as phomopsis seed decay are more likely the longer the crop is left in the field. If the seed is to be kept for next year's seed, a timely harvest is even more important. Time of harvest studies conducted by the University of Guelph have shown that seed vigour is lost if there is a delay between physiological maturity and harvest.

Equipment Adjustments

A loss of just 4 beans per square foot (0.09 square meters) represents a 1 bushel per acre (67 kg/ha) loss. Approximately 80% of combining losses occur at the header, so proper header operation is essential. Choose a ground speed that will not overrun the header's ability to do the best job possible. Setting the correct cylinder speed and concave clearance is one of the most important jobs of the combine operator. Excessive cylinder speed is the leading cause of grain damage. Try to eliminate unthreshed losses by adjusting concave clearance instead of adjusting the cylinder speed. If the beans are to be kept for seed, or are IP beans, it is even more important to minimize seed damage. One way to quickly check the amount of seed coat damage in the field is to do a Hypochlorite Soak Test for Soybeans.

Hypochlorite Soak Test for Soybeans

The soak test is a quick way to reveal unseen soybean seed coat damage. Samples are tested in the field and then the appropriate adjustments can be made to reduce damage to less than 10% damaged seeds.

Procedure:

1. Prepare a 1:5 dilution of household bleach to water (this will make a 1% sodium hypochlorite solution).
2. Obtain several shallow plastic containers, which will each hold 100 soybean seeds.
3. Take a random sample of seed. Count out four replicates of 100 seeds each, excluding splits and other obviously broken seeds. Place in plastic container.
4. Submerge each 100 seed replicate in the solution for 10 minutes.
5. Remove swollen seeds with tweezers.
6. Average the number of swollen seeds per replicate. If over 10%, adjust the combine or handling to reduce damage.

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Evaluation

Seeds can usually be separated into three different categories following the 10-minute soak test.

Firm - seeds that do not take up solution. These are considered to have little or no damage.

Wrinkled - seeds that take up a small amount of solution that causes their seed coats to blister. These seeds are only very slightly damaged.

Swollen - seeds that take up solution and appear two to three times their original size. Some may have only a large water blister at one end and others may be breaking apart. These seeds are considered damaged.

Source: Iowa State University of Science and Technology - Seed Testing Laboratory, Seed Science Center 1992

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Is a Pre-harvest Burndown Required?

A pre-harvest burndown can be used if weed pressure is extremely high. However, if herbicides are only being used to facilitate harvest, a killing frost will usually accomplish the same task. If the field is intended for winter wheat and perennial weed pressure is high (eg. milkweed) a pre-harvest burn-down may be the only option for weed control, because once the soybeans are harvested, not enough top growth will remain to kill the weeds at that time. Tramping losses must be considered, and usually range around 4% crop loss. However, a pre-harvest burndown will not mature the crop more quickly, so harvest will not be possible any sooner. Burndown options include:

Precautions

• Apply in 225 L/ha water to burn off weeds when 80% natural crop leaf defoliation has occurred and 80% of the pods have turned yellow.
• Avoid regrowth by targeting spray within 7 days of variety maturity date and harvest 5-7 days after application.
• For ground application use 1.25-1.7 L/ha (0.5-0.68 L/ac).
• For aerial application use 1.7-2.3 L/ha (0.68-0.92 L/ac).

Precautions

• Apply in 50-100 L/ha (20-40 L/ac) water when the crop is 30% grain moisture or less.
• Do NOT apply to crops grown for seed.
• Apply at least 7 days prior to harvest when pod tissue is dry and brown and 80-90% of original leaves have dropped.

Related Links

• OMAFRA Publication 75, Guide To Weed Control

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