When dry August weather hit and persisted into September, the common perception was that kernels would be light and test weights would be low. Maybe that's true in some cases, but certainly not true in all cases.
One field hit hard by both drought and signs of nitrogen shortage is still yielding well, and producing 60 pound test weight. The normal test weight for no. 2 corn is 56 pounds per bushel. Test weights below that can be subject to dock. Dave Nanda, former plant breeder and Director of Genetics and Technology for Seed Consultants, Inc., says that test weight is not an easy concept to grasp, and is often misunderstood. It is basically the weight that fills a bushel volume.
"What people don't understand is that genetics is a major player when it comes to test weight," Nanda says. "Weather may have some effect, but genetics is really the main driver for this factor."
Some hybrids tend to produce lighter, chaffy kernels under normal conditions, he says. Others produce heavier kernels. It's a characteristic that breeders track as they select hybrids.
Part of the dilemma, he says, is that sometimes hybrids that are only average for test weight are high yielders. And vice-versa, hybrids that produce the great test weight aren't always amongst the best yielding hybrids. The hybrid producing the 60 pound test weight in the field we visited recently happens to be both – a good yielder and good on test weight.
Water content will also affect test weight. The 60 pound test weight is figured on dry corn. With corn coming out of the combine at 20% moisture, the test weight will likely be lower before drying and removing the moisture, Nanda says. That's because water is lighter than starch.
The bottom line is that while test weight is important, it's not the only factor to make decisions on, Nanda says.