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Beware of Claims That High Yielding Corn Has Best Test Weight

Beware of Claims That High Yielding Corn Has Best Test Weight
Corn specialist contends no one has proven the connection.

You'll likely hear a lot of talk about test weight in corn during harvest and in the months following, whenever it finally ends. Most of it will likely be negative, because test weights are trending lower this year for a variety of reasons, ranging from excessive grain moisture at harvest to early death of leaves and plants by disease, cool weather and even frost.

Listen to discussions or sales pitches where test weight becomes an issue with both eyes and ears wide-open. You may want to double check the information and decide what makes sense for yourself before making a decision based on some connection to test weight.

Bob Nielsen, Purdue University Extension corn specialist, and Jim Camberato, Purdue Extension soil fertility specialist, have conducted a variety of trials over the past couple of years throughout Indiana, primarily to establish new nitrogen recommendations based on Indiana soils. At the same time, they've made other interesting observations. One of them reaffirms little if any correlation between yield potential and test weight, even though many argue to the contrary. They certainly saw little connection in the past two seasons, with test weights and yields jumping all over the chart so much that it wouldn't be possible to fit a straight line curve on any relationship, if there is any.

"Hybrid variability exists for test weight, but also does not necessarily correspond to differences in genetic yield potential," Nielsen comments. "Test weight for a given hybrid can vary from field to field and year to year, but does not necessarily correspond to the yield level of an environment.

"When we plotted our numbers from our own recent trials, the figure we produced illustrates the absence of a strong correlation between relative grain yield and test weight for two hybrids grown in our nitrogen rate trials over multiple years in Indiana."

Nielsen says some other common conclusions and assumptions about low test weight corn aren't necessarily proven by data. One of those assumptions is that low test weight corn results in lower processor efficiency and quality of processed end-use products like corn starch.

"The research literature doesn't consistently support this belief," Nielsen says. "Similarly, low test weight corn grain is often thought to be inferior for animal feed quality. Again the research literature is not in agreement on this. Whether or not low test weight grain is inferior to high test weight grain may depend upon the cause of the low test weight in the first place."

For example, if test weight is low because mold was prevalent on ears before harvest, then you may be dealing with a different set of circumstances. Many kernels won't have as much starch. Mycotoxins that affect species such as swine, but can also affect even dairy cattle if in the feed at higher levels, may be present, depending upon which fungus caused the mold.

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