Lower Test Weight Means Added Challenges

By Jane Fyksen Crops Editor
Thursday, October 30, 2008 7:19 AM CDT

Weather this fall has allowed late-planted corn to mature. Unfortunately, quality issues have been surfacing in some locations. A long cool growing season will often result in good yields with high grain moistures and low test weights. Lower test weight is the result of relatively more starch and lower protein n a condition that also reduces field dry down rates and increases drying costs.

Corn that hasn’t dried early in the harvest season often stops at 17 to 18 percent. That may well be the case this year, as the number of favorable drying hours is much less after Oct. 20. Producers shouldn’t anticipate much additional field drying, say Charles Hurburgh and Roger Elmore with Iowa State University.

They say to expect drying to cost about five cents per point of moisture removed. Eight points removed, down to 15 percent moisture, would cost about 40 cents per bushel plus the weight shrink. For this reason, they say there’ll be an incentive to hold corn at higher moistures, awaiting better drying conditions in the spring, blending opportunities, or higher moisture feeding.

This year, they note, dry corn test weights of 52 to 54 pounds per bushel (compared with the more typical 55 to 57 pounds) indicate incomplete maturity. Loss of N from extreme rainfall may be a contributing factor to lower test weight this year.

Ethanol processors may not be greatly affected by the somewhat lower test weight; lower protein and higher starch yields more ethanol, but does reduce DDGS quality. Pay attention to the moisture limits of ethanol plants; most stop taking corn at either 17 or 18 percent, these two advise.

Test weight is a good indicator of corn “storability.” Corn below 54 pounds per bushel after drying should not be stored into warm weather and should be dried to less than 15 percent moisture before storage of any duration. Lighter corn also will break more in handling.

Corn normally gains about 0.25 pound per bushel per percent of moisture removed - more with low temperature drying and less if corn temperatures exceed 150 degrees. “We are also learning that corn that has reached 150 degrees or more in drying is more difficult to ferment in ethanol plants. A discount for test weight in wet corn can be simply an extra discount for moisture, depending on the actual values for moisture and test weight,” say these Iowa State University crop experts.

Keying on storage, they remind growers to always cool grain quickly and minimize variations both from the dryer and from the field. “Holding wet grain, especially without aeration, shortens ‘shelf life’ considerably. Fungi grow very fast in corn above 20 percent moisture. Overnight storage of wet corn in a wagon or truck can have a marked effect on future storability,” they say. “Always get wet corn into an aerated storage immediately. Likewise the practice of holding medium moisture corn - 16 to 20 percent - for future blending or feeding opportunities will cause problems for corn stored - even after drying - into the following summer.”

They suggest the following for aeration:

- Phase 1 or Fall Cool Down: Lower grain temperatures stepwise (October, 40 to 45 degrees; November, 35 to 40; December, 28 to 35)

- Phase 2 or Winter Maintenance: Maintain temperatures with intermittent aeration (January and February, 28 to 35 degrees)

- Phase 3 or Spring Holding: Keep cold grain cold (i.e. seal fans and ventilate headspace intermittently).

“This year there will be more wet corn held because of high field moistures and expensive drying. Wet corn should be checked weekly, and monitored for temperature increases. Wet corn should have 0.2 cfm per bushel of aeration - double the normal rates for dry corn. Problems will start to show up in February and March as temperatures rise, they warn.

When large amounts of wet corn exceed drying capability, dry to 17 to 18 percent moisture and cool in the storage bin. The corn will end up at about 16 percent. Or, dry to 20 percent, cool in the bin and hold wet corn for spring.

“The less you dry, the more risk you are accepting. But spreading out the drying into spring may be the only choice. Risk will require more constant attention,” says this pair.

Be selective about what corn is placed in storage versus moved at harvest. Deliberately decide which corn and bins are going to be kept into the summer. “This should be your best (i.e. highest test weight) corn, harvested below 20 percent moisture with careful combine settings to minimize trash and placed in storages with good aeration rates/airflow distributions,” advise Hurburgh and Elmore.

Low test weight corn should not be put in temporary storage. Don’t mix corn of different crop years in the same storage bin; the mix is generally much less stable than each year’s crop stored separately. The 2008 corn will be more susceptible to mold and heating in storage than average corn at the same moisture, which means that holding wetter corn should only be done in cases where there is drying or other options to halt spoilage if it starts, they report.

Remove the center core and use a grain distributor if possible. Check your grain at least every two weeks, with some way to take grain temperatures. If a slow rise is noted, aerate. If a hot spot starts, make that the next corn to be moved out; one storage problem always leads to another.

Understand your buyers' needs, and match storage and drying practice to intended marketing time. For example, corn sold for July or August 2009 delivery should be dried more fully right away.

Cool wet conditions also favor fusarium fungi - the white or pink ear rots often found in ear corn stored too wet. Field moistures in the low 20s over a long period are favorable for these fungi, which can produce several toxins (vomitoxin, zearalenone and fumonisin) harmful to people and livestock. Grain with field mold should be tested for mycotoxins before feeding. Fields still standing should be scouted to determined the extent of ear and stalk rot fungi. Harvest problem fields (10 to 15 percent or more ear rot) as soon as you can. The longer the corn remains in the field, the greater the chance of toxin production.

Diplodia ear rot is more prevalent this season than in previous years in some fields, too. Although mycotoxins aren’t usually associated with Diplodia, grain quality will decrease substantially if the corn is allowed to remain in the field; harvest is also recommended.

Adjust harvest equipment to minimize damage to kernels since mold and mycotoxin levels tend to be at greater levels in damaged kernels. Dry (to less than 15 percent moisture) and cool (to less than 45 degrees) as quickly as possible to reduce further mold growth and toxin production.

Field damaged grain will not store beyond winter months. Maintain 1 to 2 percentage points lower moisture than normal grain (for example, 13 percent instead of more typical 15 percent). Do not try to hold field damaged corn at higher moistures to avoid drying expense. If you suspect mycotoxin problems, check with crop insurance provider to see if adjustments may be needed, and how to represent areas to be adjusted. Crop adjustments for quality problems, including mycotoxins, must be done on standing corn at or before harvest.

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