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Harvesting Wet Soybeans

You want your beans in the combine, not on the ground.

After a tough growing season for soybeans there are two more hurdles – harvest and drying.

When racing to get the soybeans off keep the combine groundspeed reasonable. It helps keep the cutterbar low which reduces losses. The best beans are often lowest on the plant. You want your beans in the combine, not on the ground.

CONSIDERATIONS BEFORE HARVEST

Depending on variety, seeding date or the amount of excess moisture received, soybeans fall into one of the following four categories this season:

Mature beans: These are the first fields to harvest. At 15 per cent moisture or less few combine adjustments are needed. Ask the buyer what moisture level is required.

Mature beans, but wet: Harvest them next. They won’t have any immature beans.

These beans would have been 95 per cent yellow-pod stage when the first frost hit. Start combining when they reach 18 per cent moisture. The beans will be tougher to get out of the pod so reduce the concave clearance and increase the cylinder speed. Check behind the combine periodically and readjust as conditions change.

Wet, mature beans with big fat green ones mixed in: These fields are mostly mature, but some soybeans were delayed. Beans from delayed areas are immature (green, soft and puffy). While these fields can still be harvested, it’s best to leave them until the green beans dry down.

Cut some green beans in half. If the green colour is limited to the seed coat, they might turn yellow in the bin.

Green, puffy soybeans can often give a little lower moisture reading. North Dakota State University recommends adding 1.5 per cent to get a more accurate reading.

Beans that had lots of green pods when they froze: These beans will never lose their green colour. If possible combine them separately. Don’t wait for these soybeans to change colour before harvesting. Harvest the field when the overall seed moisture is appropriate.

Consider screening the soybeans to remove smaller green beans before putting them in storage, avoiding significant discounts at the elevator.

DEALING WITH WET SOYBEANS AFTER HARVEST

Harvesting at 18 per cent moisture or slightly higher can be done, but drying either this fall or next spring is required.

NATURAL AIR

Air flows through beans easier than some crops and the increased airflow decreases drying time. But when the outside air temperature is cool, drying with ambient air will be limited and will take a long time.

When using natural aeration, any crop, including soybeans, will reach Equilibrium Moisture Content, where the air only has the ability to dry the beans to a certain moisture level depending on the ambient temperature and relative humidity. No matter how much more air you pump through they will not get any drier.

Reducing the depth in the bin, increasing the airflow per bushel, or adding supplemental heat to the aeration can increase drying speed.

ADDING SUPPLEMENTAL HEAT TO AERATION

Only add an extra 15 to 12C (5 to 10F). Generally, fans (and low heat burners) should be operated continuously as long as the average 24-hour air conditions are below 70 to 75 per cent relative humidity and soybean moistures are above 15 per cent. Usually only little rewetting occurs, and then only in the bottom six to 18 inches in the bin. The balance of good weather more than offsets short high-humidity periods during the night, or one to two days of drizzle.

Moreover, heat from the fan motor reduces the ambient relative humidity by 10 to 20 percentage points.

Cooling and holding beans is another option. Once frozen,

18 per cent soybeans can be stored over the winter. Once the temperature is below freezing, hold the beans at that moisture and run the fan every couple of weeks in case there are any hot spots.

Running the fan when it is freezing is expensive as the rate of drying is very slow so turn it off, but check bins regularly. Start the fans in April and continue to dry the beans down, probably until the end of May.

Harvesting during the afternoon when moisture contents are closer to 16 per cent will free up dryer capacity.

GRAIN DRYER

Typical dryer temperatures are too hot and the air is too dry resulting in excessive soybean seed coat cracking and splits. The maximum temperature for drying seed soybeans is 38 to 49C (100 to 120F).

Higher temperatures of 54 to 66C (130 to 150F) and running the dryer a bit slower is a good strategy for beans destined for the crusher where preserving good germination isn’t a concern. Keeping the relative humidity of the drying air above 40 per cent minimizes cracking, but this greatly limits dryer temperature and may not allow the throughput needed.

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