When we deliver grain, the elevator runs moisture and test weights. For corn and wheat, these measurements can impact price and lead to price dockage, because low-test weight cereal grains will not store well and will be more prone to mold. Test weight is often used when seeding small grains where rates are bushels per acre, but you are buying pounds of seed and need a seed rate in pounds per acre.
We know that test weight is one measure of grain quality. It is a volumetric measurement based on grain weight in one official bushel or 1.244 cubic feet. For U.S. No. 1 yellow corn, the official minimum test weight is 56 pounds. For soybeans and wheat it’s 60 pounds, sorghum and rye are 56 pounds, barley is 48 pounds, oats are 32 pounds, and rice is 45 pounds. Test weights are determined by weighing grain samples filled in a standard dry one-quart measure.
Test weight is a measure of density (mass/volume) and is measured in pounds per bushel. The standard test weight of 60 pounds per bushel is always used to convert the scale weight of soybean loads to the number of bushels contained in the load. This is true even if the actual test weight of the load maybe lower or higher than 60 pounds per bushel. Therefore, actual test weight doesn’t impact the number of bushels harvested from a field.
Good quality seed of low (13 percent) moisture content can be expected to have a good test weight. Test weight is recorded and rounded to the nearest tenth of a percent and soybean grades are related to minimum test weight values. No. 1 yellow soybeans have a minimum grade of 56 pounds, but are usually assigned a value of 60 pounds when converting delivery to bushels for pricing, which is based on price per bushel.
Lower test weights are more common when crops have experienced stress during seed fill or when a frost hits before physiological maturity. Early start crops like corn and cereal grains are more impacted than oil and protein seed crops. Stress can be brought on by disease, insects, soil or weather conditions that impact the uptake, production or flow of nutrients and carbohydrates to the seed during grain fill.
Test weights don’t necessarily correlate with yield. High test weights aren’t always associated with high yields, and lower test weights do not always mean lower yields. But for corn, test weights have been trending up the past decade with good management and weather conditions. See past article by Emerson Nafziger.
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.
Soybean agronomist Daniel Davidson, Ph.D posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org or ring him at 402-649-5919.