Corn test weight tends to be a topic of hot debate. A common misconception is the assumption that higher test weight corn yields more.
High-yielding fields won’t necessarily have a higher test weight, just as lower-yielding fields won’t necessarily have a lower test weight. To understand the concept, we need to think of corn yield in terms of pounds harvested per acre, not necessarily bushels per acre.
If we sold grain by the true volumetric measurement that is a bushel, hauling grain would be nothing short of a nightmare.
Imagine unloading an entire semitrailer by way of a bushel basket. It would be much more practical to sell by weight, which is exactly how we market grain.
The standard weight for a bushel of No. 2 yellow corn was set at 56 pounds, even though the weight per bushel of corn test weight can vary hybrid to hybrid, farm to farm and year to year. When you sell 1,000 bushels of corn, you are really selling 56,000 pounds of corn.
The concept is confusing because we still speak in terms of the volumetric measurement, a bushel, but weight is what our check depends on.
What about the test weight measurements taken on each load of grain? Think of test weight as just another quality check, like foreign matter, damage and so forth.
Test weight can drop to 54 pounds per bushel for No. 2 yellow corn before a price discount may be applied at market, but no premium is added for higher test weight. So, staying above the threshold is important, but striving for high test weight is not.
For example, let’s say we harvest two different hybrids from the same test plot. Hybrid A yields 12,000 pounds per acre with test weight measurement of 56 pounds. Hybrid B yields 10,000 pounds per acres and test weight measurement of 60 pounds.
Hybrid A is the clear winner because it produced more pounds of grain per acre while maintaining the 56-pound test weight threshold. Hybrid B isn’t rewarded for exceeding the 56-pound threshold. Dipping below the threshold, however, say 54 pounds or below, would likely trigger a price dock at the elevator.
This Season’s Impact On Test Weight
It won’t be unusual for areas of Illinois and Indiana to experience some incidences of lower test weights this harvest. Stress during grain fill resulting from drought and varying degrees of ear and kernel rot are likely culprits of potential test weight reduction.
Another looming factor that can cause premature plant death and, therefore, compromise test weight is a killing frost prior to black layer.
Typical first freeze dates range from the last week of September in northern Illinois to the last week of October in southern Illinois and from the first week of October for areas in northern Indiana to the last week of October in southern Indiana.
Given the extremely late planting this season, some areas are up against the clock, even with some above-average temperatures in September.
Speaking of late planting, one of the most talked about implications of a delayed spring has been a delayed harvest and managing wet grain. It’s important to note that grain moisture has an inverse relationship with test weight.
High moisture grain tends to be swollen and sticky, therefore grain does not slide and pack easily into a volumetric bushel, resulting in lower test weight. As grain dries and shrinks, test weight improves.
Test Weight Management
Managing for test weight can be tricky as it is a factor highly dependent on environmental conditions throughout the lengthy grain fill period. There are a few management factors that can help, but none are a silver bullet.
Select hybrids with consistent and adequate test weight from year to year, coupled with a good disease package and below-ground insect protection for at-risk acres.
Maintain an optimum fertilizer application plan, especially nitrogen, to ensure nutrients are available at the end of the season. Finally, reduce planting populations if you feel your soils are unable to support higher densities.
For more information related to test weight, visit www.agry.purdue.edu/ext/corn/news/timeless/TestWeight.html.
For questions about selecting hybrids for your specific geography and soil types, please don’t hesitate to contact me or your agronomic adviser.