Test weight is important with corn because if it drops too low sellers are docked and buyers can even reject the grain. And corn with low test weight just doesn’t store that well. Iowa State University extension says, “By law, a “weight” bushel of corn is exactly 56 pounds, a soybean bushel is 60 pounds and a wheat bushel is 60 pounds, regardless of the test weight. Test weight is a general indicator of grain quality and higher test weight normally means higher quality grain.”
What about test weight in soybeans? Should we concern ourselves with it? Earlier this year I wrote a blog “Understanding Test Weight” posted on ILSoyAdvisor. I concluded “Fortunately, most soybeans being harvested are No. 1 yellow and are bought with a 60-pound test weight even though it may be slightly less than that.” This did not really answer whether low test weight can be an issue in soybeans.
Emerson Nafziger wrote in a University of Illinois Bulletin article back in 2003 “Soybean test weight doesn’t seem to vary that much, and it doesn’t get much attention. Soybean seeds tend to be more regular in shape than corn seeds, and spherical shapes like soybean seed tend to fit together more uniformly regardless of size differences. A shortened seed-filling period may also result in smaller seed, but not much change in density of individual seeds.”
 However, this fall’s grain quality was an exception to the norm of No. 1 yellow soybeans, resulting in empty pods, shrunken seed (low test weight), discolored and generally poor-quality beans.
Fall Harvest 2018: Some growers were plagued by rain, which delayed soybean harvest leading to damaged soybeans standing in the field with low quality. Ignacio Ciampitti, soybean specialist at Kansas State University, wrote in his recent extension article, “Large areas of the soybean belt have poor quality soybeans that are being either severely discounted or outright refused at the elevator. In Kansas, there are confirmed reports of loads being rejected at local elevators and large terminals due to high levels of purple seed stain. One reason for these rejections could be due to a reduction in feed value.”
We know that August rains are crucial to soybean yield, however too much can set up a risk of infection. Ciampitti explained that excessive rain during the reproductive stages provided an opportunity for infection by pod and stem blight, purple seed stain, and anthracnose. Further rain during and after maturity allowed these diseases to develop and were responsible for poor quality seed.
Ciampitti listed three options for growers if their field-harvested soybeans were of poor quality.
  • Feed to livestock
  • Dry and store
  • Blend with good seed
For more information on using soybeans as cattle feed, please see an article from the University of Nebraska: Can Damaged or Discolored Soybeans be used as Cattle Feed?
Elevator Considerations: Does test weight matter at the elevator or at its destination—a crush plant? Soybean test weight is normally pegged at 60 lbs. per bushel, but at delivery often comes in at 56 to 58 lbs. Richard Galloway, retired soybean crush expert said “Test weights below 54 (lbs.) are docked at most receiving sites. The only reason for this (dockage) is that storage bins and processing equipment are limited by volume. That is, a storage bin holds fewer lbs. of low-test weight soybeans than normal beans. An extractor in a processing plant is limited by volume, not weight, so the crush rate of a plant is less crushing low-test weight beans than normal beans.”
However, if low test weight soybeans also show signs of mold and purple staining there is risk of dockage for damage and shrink. Every elevator that receives soybeans has a discount schedule. Discount schedules are important because they communicate how and when various shrink factors, damage or foreign matter discounts are applied at delivery. Elevators allow up to 2% damage in soybeans. To learn more about handling wet and damaged soybeans click here to read a recent article from Iowa State University.
Soybean agronomist Dr. Daniel Davidson posts blogs on topics related to soybean agronomy. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919. 

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About the Author: Dan Davidson

Soybean agronomist Daniel Davidson, Ph.D., posts blogs on topics related to soybean agronomy. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.