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Channel® Field Check Up Grain Test Weight May Be A Factor In 2017
MORGAN SCHMIDT
LUBBOCK, TEXAS
In all of the talk about corn yields, the importance of grain test weight is often lost in the conversation. With this year’s challenges of late-planted and replanted corn fields, test weight may be an important factor to consider during harvest. Lower test weight usually indicates that the crop did not mature entirely or was subjected to stresses. High test weight corn is more desirable because it means the kernels have a higher percentage of hard endosperm.
Corn in the United States is sold on a weight basis in a 56 pound block called a “bushel”. Historically, a bushel is a measure of volume, not weight, equivalent to 32 quarts or 1.2445 cubic feet. Because the logistics of selling by weight make more sense than by volume, a standard was set that each 56 pound measure of corn would be considered a bushel.
When it comes to the logistics of grain handling, it makes sense that higher test weight corn would be more desirable. Transportation and storage of low test weight grain is more expensive per pound, so it is often discounted by buyers. Higher weight in a smaller volume is advantageous in handling and storage as well as during harvest because more bushels will fit in the truck, bin, or grain tank of the combine.
Test Weight vs. Moisture
There is generally an inverse relationship between test weight and moisture; test weight increases as moisture level decreases. Because kernel dry matter is denser than water, proportionally as the amount of water decreases, the bulk density of the kernel increases. How much test weight increases upon drying varies based on the corn product, grain condition and drying temperature. Drying from 28 percent down to 20 percent moisture content generally results in an increase in test weight because seeds shrink and get denser. A change from 20 percent to 15 percent; however, can actually decrease test weight in some cases because kernels can lose moisture weight without a change in size or shape.2
Occasionally there is confusion regarding how drying grain can increase its value, the implication being that drying can increase the weight of grain. Although the cause is not fully understood, studies have shown that slow drying with natural or low-heat air can result in greater increases in test weight than fast drying with high heat.
Research was conducted at the University of Minnesota to assess the effect on test weight from plant death at different stages of development prior to natural black layer formation. It was found that test weight will vary based on the stage corn had reached before grain fill was ended. Immature ears were taken at various stages from soft dough through full maturity and dried at 80 and 120 degrees F. The study showed that those kernels that had reached soft dough and early dent actually decreased test weight after drying, whereas there was an expected increase at all other stages. Increase in test weight will depend on stage of development, kernel moisture and grain quality and drying temperature. The general result of this study found that if corn is well dented or beyond in maturity, some increase in test weight should occur with drying.1
Test Weight vs. Density
Test weight, however, is not only a function of density, as other factors also determine test weight: how well kernels fit together (size and shape), how slippery the seed coats are, and other physical characteristics. In some cases, seeds that fill a little longer and get heavier can actually lose test weight due to shape changes. Test weight can also be a good indicator of storability, as it generally decreases as grain deteriorates.
Other factors contributing to lower test weights include any plant stresses that impact nutrient movement and grain fill, such as, diseases, insects, soil fertility and environmental conditions. To learn more about test weights in your fields or for help choosing corn products, consult with your Channel Seedsman.
Sources:
1 Hicks, D. 2004. “Corn test weight changes during drying.” Minnesota Crop News.
http://blog-crop-news.extension.umn.edu/2004/09/corn-test-weight-changes-during-drying.html.
2 Nafziger, E. 2003. “Test weight and yield: A connection? The Bulletin.” University of Illinois. http://bulletin.ipm.illinois.edu/pastpest/articles/200323h.html. Web sources verified: 07/28/2017.
Monsanto Technology LLC. Channel® and the Arrow Design® and Seedsmanship At Work® are registered trademarks of Channel Bio, LLC. ∆
MORGAN SCHMIDT: Channel Agronomist
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