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Variability will be key issue to manage in 2019 corn and soybeans



Iowa Correspondent

AMES, Iowa – Due to late planting delays and inclement weather throughout this year’s growing season and into harvest, variability will be the key issue to manage in 2019 corn and soybeans, which will eventually effect test weight this fall, according to Iowa State University (ISU).

In an Oct. 10 ISU crop report, Charles Hurburgh, ISU professor of agricultural engineering and manager of ISU’s Iowa Grain Quality Research Laboratory, and Alison Robertson, ISU associate professor of plant pathology and microbiology, said this year continues the chain of growing seasons, with extremes and rapid changes that have gone beyond expectations.

“This made for periods of both stress and favorable crop growth despite the planting dates,” Hurburgh and Robertson said, adding that frost, potentially killing in the northern half of Iowa, had already been forecast.

“The USDA data indicated a wide range of maturity due to planting date, but the periods of hot weather scattered through September and early October may have reduced the potential for very high-moisture corn and soybeans,” they added.

As a result, test weight, which is a measurement of bulk density or weight of a unit volume of grain and of general overall grain quality, will be down this fall, Hurburgh told Farm World.

“It’s driven by the planting date and lack of maturity,” he said. “The effect is on handling and storage. The lower the test weight, the lower the shelf life. Once the test weight is really low (40 lbs. per bu., or less), it probably won’t have a lot of impact on nutrition and digestibility.”

ISU reported that corn test weight values can range from 45 lbs. per bu. to over 60 lbs. per bu., with the USDA having established the standard test weight of a bushel of corn as 56 lbs. per bu., based on 15.5 percent moisture content.

“As long as you know what the protein is and balance test weight, then digestibility will be OK,” Hurburgh added. “But you might have to put more soymeal with it. The legal test weight is 56 lbs. per bu. If we are above 50 lbs. per bu., we won’t notice it that much.”

For example, with corn, normal-to-very late planting guarantees a large range in maturity and harvest moisture, Hurburgh and Robertson said.  

“Test weight, which is a good indicator of maturity, will probably average 54-55 lb. per bu. - less than the long-term average of 56-58 lb. per bu.,” they said. “Lower test weight means more handling breakage, shorter storage life, and often higher drying costs per unit of water removed.

“On a weight basis, feed value and digestibility does not decline significantly until test weights fall below the mid-40s,” they added. “Producers should check the test weights from each field/hybrid. The lightest corn should be sold first.” 

Hurburgh and Robertson said test weight should increase about 0.2 lb. per bu., per percent of moisture removed; increases less than that indicate immaturity.

“Early death from frost typically creates low test weight grain that does not increase much during drying,” they said. “The detrimental effect of low test weight is primarily on storage and handling. More fines will be created in handling, which increase storage issues by restricting airflow.”

But as long as low test weight grain is formulated by weight and not volume, the feed value is not greatly reduced.

“On a weight basis, ethanol yields should not be effected unless there has been spoilage,” they said. “Variable grain quality means more variability in storage. Try to even out moisture going into dryers by not mixing grain from areas with large differences in quality.

“Dryers will not even out variable input corn,” they added. “Grain elevators will have more difficulty controlling uniformity because deliveries cannot be controlled.”

But elevators will likely be paying more attention to test weight, Hurburgh told Farm World.

“Most of the time, they don’t pay much attention once the grain gets dried,” he said. “The test weight goes up once the grain is dried, but water loss will increase test weight.”

At the end of the allowable storage time, grain will have lost about 0.5 percent of weight and will have increases in damaged kernels enough to reduce its grade by one number, which in general would trigger damage discounts in the market as well, Hurburgh and Robertson said.

“With the expectation of lower test weights even in fully mature grain, these storage times should be reduced,” they said. “Variability plays a big role in storage life because if there are pockets of wetter (and likely lighter) grain, those pockets will behave as wetter grain would, not the dry average.” 

For this reason, the researchers said this would not be a good year to hold wet grain before drying, even for short periods. 

“A load of 24 percent corn left on a truck for a day could lose half its storage life in that day; more if it were immature and low test weight,” Hurburgh and Robertson said. “Additionally, from a mycotoxin perspective, fumonisin levels can increase in the time between harvest and drying.

“Minimizing wet-holding time is critical to quality and safety maintenance.”


Photo cutlines:

Photo #1: Charles Hurburgh, Iowa State University (ISU) professor of agricultural engineering and manager of ISU’s Iowa Grain Quality Research Laboratory, told Farm World test weight, which is a measurement of general overall grain quality, will be down this fall (photos courtesy of Joseph L. Murphy/Iowa Soybean Assoc.)

Photo #2: Pushing into November, weather continues to be the main factor in farmers’ ability to get their crops harvested, said Charles Hurburgh, Iowa State University (ISU) professor of agricultural engineering and manager of ISU’s Iowa Grain Quality Research.