36 Thank You for Your Trust & Time, Since 1999 Better Farming | December 2024 Each fall at the beginning of corn harvest, the discussion, debate, and sometimes arguments surface around the subject of test weight and its impact on yield. The premise being that high test weight corn is high-yielding corn and low test weight corn equates to low-yielding corn. This is easily settled by tracking and plotting both test weight and yield. When you do, it becomes evident there is no relationship. Test weight measurement on corn is a man-made test; it is not a yield component. It does not involve the yield components of number of cobs per acre, or kernels per cob, or even kernel weight. It is simply the weight of kernels that can fit inside a half-litre cup. The weight might have more to do with kernel shape, size, or how slippery it is, allowing individual kernels to slide by one another. The methodology is described in the Canadian Grain Commission Guides: greatlakesgrain.com/Products-Services/Canadian-Grain-Commission-Guides. The test weight is important for grading and pricing the crop upon delivery to an elevator or end user. Most contracts specify No. 2 yellow corn with a usual minimum bushel weight of 53 pounds per bushel. Below this weight, discounts are applied. That would be the primary concern for having a good test weight. Test weights are also an indicator of grain quality and how well the grain fill period progressed in the later stages before R6 black layer. Lower test weight is often attributed to stresses that occur prior to or during grain fill period. Early frost damage is often the main concern for interrupting grain fill and causing low test weights. Most often, a late planting season contributes to: The risk of a fall frost lowering test weight; weather stresses such as drought; lack of sunshine during grain fill that can lower photosynthesis and produce less sugar to fill the kernels; loss of green leaf area due to a combination of stresses; and nutrient deficiencies – most notably nitrogen and potassium – and diseases such as foliar pathogens like tar spot. These can all interfere with the normal progression of grain fill and result in low test weight corn. Hybrids can be a factor, but they are also influenced by the growing environment and management. Last year, I had the same hybrid in seven different locations and the test weight varied from 54.2 to 57.7 pounds per bushel. This is the time of season for test plot harvest. Pay attention to the results. Seldom will the highest yielding hybrid have the highest test weight. Low test weight corn is not fun to harvest. Drydown in the field is very slow. CORN TEST WEIGHT VS. YIELD: A DEBATE Debunking the test weight myth. By Dale Cowan crops: yield matter$ The data above is from 2023 and shows the relationship of test weight to yield. (n=170) Test weight lbs per bushel Yield bushel per acre
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