Article by Dale Cowan
Agronomy Strategy Manager and Senior Agronomist
AGRIS Co-operative - CENTRAL OFFICE
As corn harvest season arrives each fall, discussions around the relationship between corn test weight and yield inevitably arise. Many believe that higher test weight implies higher yield, while lower test weight means lower yield. The easiest way to settle the discussion is plotting multiple samples of yield and test weight over time, which shows no significant relationship between the two.
Understanding Test Weight and Yield
Test weight, though unrelated to yield, is essential for determining corn quality and grade. Yield is driven by the number of cobs, kernel count, and kernel weight, while test weight simply measures the weight of kernels in a half-liter cup as outlined by the Canadian Grain Commission.
Factors Impacting Test Weight
Test weight often reflects how well the grain-fill period developed, and lower test weights typically result from environmental and management stresses. Early frost damage, a common cause, can disrupt grain fill and reduce test weight. Weather challenges, such as drought, insufficient sunlight during grain fill, or limited green leaf area, can reduce photosynthesis and sugar production, compromising kernel fill. Nutrient deficiencies, especially in nitrogen and potassium, as well as foliar diseases like Tar Spot, further interfere with normal grain fill, leading to lower test weight.
Hybrids also play a role; however, environmental factors and management significantly impact each hybrid’s performance. For example, one hybrid tested at seven locations last year showed test weights ranging from 54.2 to 57.7 lbs. per bushel, underscoring the role of external conditions.
Harvesting and Storage Challenges with Low Test Weight Corn
Low test weight corn can present unique harvesting challenges. With slow drydown in the field, these kernels often contain tiny voids that hinder moisture migration and evaporation, slowing the drying process both in the field and through mechanical drying. To compensate, operators may raise drying temperatures, which risks caramelizing kernels or, in extreme cases, causing dryer fires. Additionally, low test weight kernels are prone to cracking, contributing to fines in storage. These fines can lead to moisture rebound when temperatures drop, impacting long-term storage stability. For this reason, a marketing plan to sell lower test weight corn promptly is advisable, as it’s not ideal for extended storage.
Selecting the Right Hybrid
When selecting hybrids, focusing solely on test weight may be shortsighted. Characteristics like yield potential, flowering dates, maturity, adaptability to soil type, and ideal planting populations are key considerations. Engaging with our Crop Specialists can help ensure the right hybrid selections for each farm and field, optimizing overall yield potential.
Below is a 2023 chart showcasing our decade-long study that we’ll continue in 2024. The R² value of 0.075 clearly demonstrates that there is no strong correlation between test weight and yield, reinforcing that test weight alone is not a predictor of yield.

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