corn in the field
WEATHER IS WHY: Even though test weight is a highly inherited agronomic trait, it can vary from one season to another, field to field, by planting date and by disease susceptibility.

Unusual growing season may impact test weight

Breeder’s Journal: If corn test weight is lighter in some cases this year, don’t be surprised.

Lots of corn was planted late this year. There were many cooler nights during this growing season, which affected maturity. Cooler temperatures allow corn plants to live longer, but grain from late-planted corn is usually higher in moisture. How will test weight be affected by the weather this year?

First, let’s review what test weight is and why it is important. It’s a ratio between weight and volume, and is measured as the weight of grain that fills 32 quart containers. There are 32 quarts in a bushel basket. So the weight of grain in 32 quarts is the test weight.

It’s really not a fixed quantity or value. Corn is marketed in the U.S. on the basis of 56 pounds test weight per bushel. We assume that was the average grain weight when the grading system started. Corn with 56 pounds per bushel can qualify as No. 1 yellow corn if no other factors lower the quality. Corn with 54 pounds per bushel will be no higher than No. 2 yellow corn. You’re docked at the elevator if your corn has less than 56 pounds test weight, but aren’t credited if your corn has higher than 56 pounds per bushel test weight.

When test weight matters
Higher test weights give you bragging rights. Also, you’re able to haul more bushels of higher test-weight grain in the truck to the elevator as compared to lower test-weight grain.

Higher test-weight grain is better able to maintain its integrity than lower test-weight grain during shipping. Hybrids with higher test-weight ratings at maturity are most likely to maintain those values. You have less chance for getting docked at the point of sale.

Even though test weight is a highly inherited agronomic trait, it can vary from one season to another, field to field, by planting date and by disease susceptibility. However, if you compare two hybrids in side-by-side test plots, the hybrid with higher test-weight ratings in your company’s seed book should remain higher than the hybrid with the lower test-weight ratings.

Other factors
This statement about the comparison between hybrids will be true unless other factors like disease resistance affect them differently. A hybrid with a higher test-weight rating hypothetically can become the victim of a leaf or ear-rot disease that can adversely affect yield, grain moisture and test weight. Late-season leaf and ear diseases and late-season drought stress tend to decrease test weigh because they interrupt grain fill and proper grain development. These factors affected test weight in some areas in 2017.

So how important should test weight be in your hybrid selection process?

There’s no relationship between test weight and yield. If I must decide between a hybrid with highest yield potential with average test weight and a hybrid with the highest test weight and average yield, I’ll pick the first one, as long as both have similar disease-tolerance packages.

Nanda is president of Agronomic Crops Consultants LLC. Email him at [email protected], or call 317-910-9876.

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