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  • Writer's pictureRachel

Impacts of rainfall on soybean grain quality and storage

Updated: Oct 18, 2018

This growing season has been a roller coaster ride for soybeans. An early warm window allowed for some early planting of beans, with a significant amount getting in the ground before May 1st. This was followed by a hot and dry May, leading into a significantly dry June and July. Yield potential seemed moderate at best until we caught some early August rains. These rains dramatically increased our yield potential and we seemed to be looking at a pretty decent soybean crop. But the year wasn’t over yet. A very wet window early in October resulted in massive moisture absorption by the beans resulting in pod splitting and grain loss. So after all of these ups and downs, where does this last hill leave us? This blog post will focus on what happens with a wet harvest season, the impacts on grain quality and what that means at the elevator, and tips for storage.

A Wet Harvest Season

Across the Pederson Seed area, rainfall amounts have ranged from 4.21-6.25 inches in the first 10-12 days. This makes up anywhere from 15-24% of our growing season rainfall. While we appreciate the rainfall and all it has done to help recharge our subsoil profile, it has reduced our number of suitable days for field work substantially. This has also resulted in some complications for our soybean crop as well. Initially the wet weather increased soybean moisture. Prior to the rains, many reports were coming in with moisture around 14-16%. This rain began to increase moisture by keeping pods saturated. With the prolonged rainfall, this pod saturation allowed the beans to keep increasing in moisture to the point where beans began to swell and split the pods open. On many of these beans, you could begin to see some slight swelling of the radical, indicating that moisture was above 50% and germination was feasible. This is a fairly rare occurance as beans must get below 50% moisture to reach physiological maturity, and then gain moisture to increase above 50% to actually germinate.

Fortunately, the weather began to dry up further preventing any germination in pods or on the ground. Of the swollen seeds whose pods had split open, probably around 0-30% actually germinated. This increase and decrease in moisture has some negative effects on pod structure and soybean quality. The more times the soybeans themselves shrink and swell, the lower their quality can be. This can also contribute to a poor seed coating, decreased viability, and potential seed splitting. This also affects the pods themselves by weakening the pod to the point where the side seams split open and release the seeds. This is actually a natural mechanism in soybeans as a means for a plant to spread its seed and propagate the next generation. However, this is not desirable from a conventional farm management scenario as we are trying to maintain and sell as many bushels per acre as possible. Plant breeders have spent years breeding this quality out of soybeans. This often results in varying scores by variety for shatter. While this is the case, at some point, environmental conditions override breeding and soybeans will shatter. As for the pod splitting that has occurred over the past week, exact percentages are unknown and highly variable across fields. While it seems fairly drastic and poor looking from the road, some estimates put split pods around 0-5%. We may see more splitting or shattering in the coming week as things stay dry and pods potentially shrink up a bit, however, it appears we will have moved past the issue of soybeans germinating in pods. Beans that have not fallen out of pods appear to be fairly stable for the time being.

Impacts on Grain Quality

As I mentioned before, repeated and exaggerated wetting and drying of the soybeans themselves can result in decreased grain quality. Additionally, higher moisture levels can also contribute to a host of fungal and bacterial diseases. Some of the fungal diseases include Diaporthe pod and stem blight, frogeye leaf spot and anthracnose. While these are not directly pod and seed diseases, they can affect the seed quality. Saprophytic fungi also will also infect soybeans and can result in discoloration of soybean seeds. Purple seed stain can result from cercospora infection and also result in discolored seed. All of these diseases can result in reduced seed germination, and reduced oil and protein concentrations. Again, the more rainfall received, the higher chance of these fungal diseases. These diseases can all overwinter on soybeans and can result in infection in subsequent years. It can also be maintained on seeds and transmit to the next generation of plants. Consequently, its important to use crop rotations to reduce inoculum and avoid bin run beans that were seed infected. Foliar fungicides earlier in the growing season can help prevent some of these diseases, particularly if applied at R5. However, residual from these fungicides may no longer have efficacy at this stage of maturity.

Beans delivered to the elevator will be docked for quality issues resulting from fungal activities or seed stains. Seeds that are split will also receive a dock at the elevator. Generally elevators will dock soybeans with more than 20% splits. However, discounted prices for lowered grain quality from disease or splits will depend on the local market and elevator decisions.

Tips for Storage

Storing beans that have been impacted by high moisture and fungal activity should be treated a little differently for bin storage. This includes beans with cracked seed coats; they will be more prone to deterioration and splitting. First, avoid mixing good quality and poor quality beans. Mixing good beans with those that are split, sprouted, discolored, or diseased will lower grain quality when selling.

If storing beans in the bin, it is important to get the seed down to a uniform lower moisture content. If storing soybeans over winter, shoot for 13%. If storing beans over summer or closer to a full year, aim for 11-12% moisture. You best bet for getting beans through the winter without further contamination of the rest of the bin or spoilage is to cool the contents of the bin down to 32-35 degrees. It can be more difficult to get beans to this temperature with temperatures this week in the 60s. Remember the dew point is an estimate of the lowest temperature you can cool the grain to on a given day. That means for the next couple days, if drying overnight, the temperatures the dryer is pushing through the bin is around 38 degrees. This should beneficial for drying and cooling. Keep checking various spots in the bin as temperatures will not always change uniformly. As we approach spring, pay attention to the south side of the bin as it will have more solar gain and grain temperature can increase more rapidly than the rest of the bin.

After beans are cooled to the ideal temperature, make sure to shut up openings to prevent snow or rain form getting in through openings. Additionally, keep monitoring bins routinely for temperature changes. Keep an eye out for insects, temperatures, and condensation as indicators that something might be going wrong with your stored grain. Ultimately, with compromised grain quality, storage time may need to be kept to a maximum of six months. More intensive management may be required beyond that point.


A tough growing season followed by significant amount of rains led to pod splitting, decreased quality, and soybean germination. Pod splitting appears to have affected around 0-5% of pods. The decrease in quality is at an unknown percentage. A decrease in quality will result in dockage at the elevator. If storing lower quality beans in a bin, make sure to keep it separate from good quality beans, dry it to 11% for long term storage and 12-13% for 6 month storage. Keep the grain temperature around 32-35 degrees. Make sure to keep an eye on grain quality and temperature in bins to prevent spoilage.


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