Harvesting Soybeans in Late Fall

If the growing season was not enough of a challenge, there are two more hurdles yet to get over – harvest, and because of the cool season, drying.

As you race to get the last of your soybeans off before the weather closes in, try to keep your groundspeed reasonable. This helps keep the cutterbar low to the ground and reduce losses. The best beans are often lowest on the plant and you do not want to leave them on the ground behind the combine.

Part 1: Considerations before Harvest

Most of the fields that reached full maturity before the frost have already been harvested and we are now dealing with soybean fields that didn’t fully mature before the frost and as a result they have some level of immature beans in them.
Depending on variety selection, seeding date or the amount of excess moisture you received during the cool growing season the soybeans that are still out in the field fall into one of the following two categories:
1) Wet, Mature Soybeans with Big Fat Green Ones Mixed In
These fields are mostly mature, but the soybeans were delayed in the low spots in the field or areas of the field that were hit with iron chlorosis earlier in the summer. Beans from these delayed areas are immature (green, soft and puffy). While these fields can still be harvested (especially as we get closer to snowfall) it would be best to leave them until the green beans dry down. If the green beans are cut in half and the green colour is limited to the seed coat they might turn yellow in the bin.
Be careful when taking moisture readings on these samples as these green, puffy soybeans can often give you a little lower reading on the moisture meter than the sample actually is. Recommendations from North Dakota State University indicate that you should add around 1.5% to get a more accurate reading.
2) Soybeans that had Lots of Green Pods when they Froze
These fields did not mature before the frost. Soybeans within most of the pods will be immature as they did not reach physiological maturity. Upon drying the seeds will shrivel. The amount of shriveling will relate to how immature they were at the time of freezing. Soybeans with shriveled, frozen seed coats are considered damaged. You are allowed 2% damaged before deductions are applied. Immature beans will be very high in moisture and will take a longer time to dry down in the field so don’t be surprised with moisture readings well over 25% at this time of the year. These immature beans will never lose their green colour so if possible combine areas of the field that had more green patches separately. Harvest the field when the overall seed moisture is appropriate.

Part 2: How to Deal with Wet Soybeans after Harvest

Harvesting at 18% moisture or slightly higher can be done, but drying – either this fall or next spring is required. Some immature fields that are measuring at 25% moisture are just too wet to harvest. These beans will be easily crushed and drying costs will be prohibitive. Freezing them in the bin and drying with aeration in the spring will take too much time and they might spoil before they dry down. Ask yourself if you would put 25% wheat in an aeration bin at this time of the year and be comfortable with it. The quality of the soybeans will probably be very poor too.
Natural Air
Air flows through beans easier than some crops and the increased air flow decreases drying time. BUT when the outside air temperature is cool, drying with ambient air will be limited and will require a long time. The higher the moisture in the beans, the longer it takes to dry them down.
When using natural aeration any crop, including soybeans, will reach an 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. Cool, moist air does not have much drying ability.
Drying speed can be increased by reducing the depth in the bin, increasing the airflow per bushel, or by adding supplemental heat to the aeration.
Adding Supplemental Heat to Aeration
When adding supplemental heat we are talking about only an extra 3 to 5.5°C (5 to10°F). Generally, fans (and low heat burners) should be operated continuously as long as the average 24-hour air conditions are below 70 - 75% relative humidity and soybean moistures are above 15%. Usually only little rewetting occurs, and then only in the bottom 6 to 18 inches in the bin. The balance of good weather during the day or week more than offsets short high-humidity periods during the night, or 1 to 2 days of drizzle. Additionally, heat generated by the fan motor reduces the ambient relative humidity by 10 to 20 percentage points.
The limitation on drying capacity can be further reduced by only harvesting during the afternoon hours when moisture contents are closer to 16%.
Cooling and Holding Soybeans Over Winter
You can put 18% soybeans in the bin and hold them overwinter once things have froze up. 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 them down, probably until the end of May.
Grain Dryer
Typical dryer temperatures are too hot and the air is too dry resulting in excessive seed coat cracking and split seeds. If you are growing the beans for seed then 38 - 49°C (100-120°F) should be the maximum temperature. If you are drying crush beans you can go higher because you are less concerned about reducing the germination or increasing the splits. A temperature of 54 - 66°C (130-150°F) and running the dryer a bit slower is a good strategy. Keeping the relative humidity of the drying air above 40% minimizes cracking, but this greatly limits dryer temperature and may not allow the through-put needed. Again, this is more of a concern with non-crush beans.
Check the Bins Regularly
If you are storing beans that aren’t dry then you should check them regularly even if they are on air. Immature pods will tend to flow to the outside as you fill in the bin. These pods restrict air flow through the bin and are higher in moisture which could cause a hot spot. Especially at this time of the fall when temperatures are above freezing consider pulling a load or two out of each bin. This will give you an idea if there is any heating and will help break up hot spots. During the winter put the fans on every couple of weeks to help keep hot spots from developing.
For further information, contact your GO Representative.