The Value of High Test Weight Corn Grain
Field Facts written by Agronomy Sciences.
According to corn extension specialists, low test weight grain may be due to any number of causes that reduce kernel fill: lower temperatures, leaf diseases or drought stress during the grain fill period, premature frost damage to late-developing fields and ear rots. Hybrid genetics also has a large influence on test weight. This article discusses test weight and its implications for grain marketing, transportation, storage, quality and feeding.
For Grain Trading, “Bushel” is a Weight Measure – Although “bushel” is technically a volume measure, grain is marketed by weight, not by volume. For this purpose, a “bushel” of corn is defined as 56 lbs. of grain at a moisture content of 15.5%. But because grain differs in kernel hardness or density, the volume occupied by 56 pounds of grain may vary substantially. Grain mass per unit volume, or density, is most important in grain transportation and storage. Denser kernels require less space, which means that fewer truckloads and storage bins are needed to store the same weight of grain. Denser grain also has higher quality characteristics for some end uses.
What is Test Weight? "Test weight" is simply a measure of grain bulk density. An official test weight measurement uses standardized equipment to determine the mass (weight) of a sample quart of grain, and then converts this to a pounds per volumetric bushel basis. Because transporting and storing lower density grain is more costly (on a weight basis), buyers discount grain if test weight is below the minimum standard set by the USDA (Table 1). In addition to density, test weight is affected by how kernels pack in a container, which is influenced by kernel shape and surface friction.
Table 1. Minimum test weight standards
for USDA corn grades*.
|USDA Corn Grade
||Test Weight (lbs/bu)
* Damaged kernels, % broken corn and foreign
material also affect the USDA grade.
As the table shows, the minimum test weight for No. 2 corn is 54 lbs/bu. Loads testing below this minimum will usually receive a dockage at the elevator.