Corn Is Drying Down Slower Than Usual In Fields This Fall

Corn Is Drying Down Slower Than Usual In Fields This Fall

You can let corn dry some more in the field if grain moisture is still high in October, but don't wait too long.

When corn reaches maturity later than normal, drydown of the grain in the field in the fall is slower due to cooler air temperatures. Corn grain drydown in fields across Iowa is shaping up to be a big issue this fall.

There are many factors that will affect the rate corn dries down while it is still on the stalk standing in the field, says Paul Kassel, an Iowa State University Extension agronomist at Spencer in northwest Iowa. Some of those factors are obvious – like hybrid maturity, and the amount and duration of sun and wind activity. Also, the number of rainy days will affect the rate and amount of grain drydown – since little or no grain drying occurs during rainy conditions.

NEEDS HEAT: "In October the potential for corn grain to dry down in the field for this year's late maturing corn crop is not real high," says ISU Extension agronomist Paul Kassel. "It will take some unusually warm weather in late October to achieve high levels of field drydown."

"Grain drydown is like any other air drying activity," says Kassel. "It requires heat to lower the relative humidity and requires air movement to assist the drying process. One way to estimate the drying power of the air is to use Growing Degree Days or GDDs. The use of GDDs to estimate corn drydown is not a perfect predictor, he says, but it does give a general idea of the potential for field drydown to occur.

GDD accumulation can give you an idea of potential for drydown
The table accompanying this article shows the expected GDDs for northern Iowa. Kassel put this table together last week. Information on GDDs for 2009 is also listed, since the fall of 2009 was a challenging fall for field drying of corn and for harvest. One bright spot in the 2009 data shows one week in November that equaled the typical GDD accumulation for mid-October.

Expected Growing Degree Days for northern Iowa


2014 dates





—GDDs base 50 North Central Iowa—










































Generally, it takes 30 GDDs to lower grain moisture in the field each point from 30% to 25%, says Kassel. Field drying corn from 25% down to 20% requires about 45 GDDs per point of moisture removed. "Sources of information on GDD requirements for rates of field drydown do not all agree," he notes. "For example, some Ohio information shows that GDDs needed for one point of field moisture loss ranges from 22 to 29 GDDs per point."

Information from a field study by corn agronomist R.L. Nielsen at Purdue University shows that rates of grain drydown can be 0.75 to 0.50 point per day in late September and early October. However, rates of field drydown usually slow considerably once mid-October occurs, adds Kassel.

Much of the corn crop in northwest Iowa this year reached maturity on about October 1. Corn grain moisture is usually about 30% once corn reaches black layer maturity. "Therefore, the potential for a lot of field drydown of corn occurring with this year's crop is not real high," says Kassel. "It will take some unusually warm late October weather to achieve high levels of field drydown."

More on stalk rot, and corn dry down in the field
Stalk rots and corn drydown are two issues that are tied together and farmers may have some tough decisions to make. Artificial drying can certainly test a grower's patience, says Clarke McGrath, an ISU Extension field agronomist at Harlan in western Iowa. As energy prices (especially LP gas) climb and/or availability of LP becomes an issue, costs can really add up. "All this makes us appreciate any natural drying that Mother Nature can provide," he says. "This fall, leaving corn in the field to dry naturally for too long may be problematic in some fields and areas of fields, for a couple reasons." They are:

• Stalk rot has gotten worse. Stalk rot and the resulting standability issues are being found in more and more fields as we enter October, says McGrath. If you can scout your corn well and find areas that have good stalk quality, then some field drying may be in order. For fields with significant stalk rot and risk of lodging, the risk/reward tradeoff of the corn in the field drying vs. harvesting the grain wet and artificial drying it is worth a good look.


• Risk of lodging and ear loss is rising. Unfortunately, this time of year the risk of the corn lodging escalates and the reward of natural field drying typically decreases. "We have had tough luck getting a lot of GDD's for speeding along maturity and drying in the last month, around 20% below average. And as we head further into October field drying usually slows even more," says McGrath.

• What about artificial drying? Compare the risks involved with field dry-down of corn to the costs of your artificial drying options—such as harvesting corn wet and drying it with a grain drying system on-farm or hauling and having it dried commercially at the elevator. You can make this comparison with the help of two new ISU Ag Decision Maker online decision tools, now available with their September 2014 updates.

Click on these links: Estimating the Cost for Drying Corn and Grain Drying and Shrink Comparison.

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