While most of the attention on crops will be focused on yield in the coming weeks, test weight also has the potential to be an issue, according to Charles Hurburgh, a professor at Iowa State University and head of the grain quality laboratory there.
“It could be (an issue this fall),” Hurburgh says.
The question right now is probably one of moisture. If there is drought in an area but the plants don’t necessarily die prematurely then the test weight could potentially go up. But if the corn plant dies early, weight could become a problem.
That was a topic of discussion after the derecho that ripped through Iowa two years ago. Most farmers and analysts thought there would be light corn that year, but Hurburgh says the state benefited from two months of excellent weather after that derecho and the corn managed to mature, although there were some grain quality issues.
Hurburgh stresses that test weight doesn’t impact yield measurements. Buyers automatically determine yield by weight by simply dividing the weight of the grain by 56 pounds, no matter what the test weight is. That means a higher or lower test weight doesn’t necessarily mean more or fewer bushels. But a low test weight will mean less weight per measurement of volume.
He says it is important to note that test weight is also dependent on grain moisture levels. The test weight is based on dry corn (about 15% moisture). As corn dries it loses some test weight due to the loss of moisture. As a general rule of thumb, it will lose about 0.2 lb. per point of moisture. Using that criteria drying a bushel of corn from 20% down to 15% should change the test weight by a pound.
Normal test weight is about 56 lbs. per bushel. A lower test may not be an issue for many end users of the grain. It makes relatively little difference for hog or cattle rations, Hurburgh says. It can make a difference in poultry rations because the birds are small enough that they can’t make up for the difference in weight by consuming a larger volume of grain.
Right now, Hurburgh says, it is too early to determine what will happen with test weights this fall but growers will know more in just a few weeks.
