With corn grain stubbornly retaining moisture in the field, growers will have to decide whether to trade some yield losses by allowing the crop to dry in the field, or add the costs of mechanical drying, noted Scott Sanford, University of Wisconsin-Extension/Madison agricultural engineer.

“Growers will have to balance time needed to complete harvest, crop condition (lodging) and increases in field losses during combining with savings in drying costs from delaying harvest,” he said.

The wet fields that have delayed growers from harvesting increases the risk for yield loss from wildlife damage and weak plant integrity due to unfavorable weather conditions, said Peter Thomison, an Ohio State University Extension agronomist. And although delaying harvest has little to no effect on grain quality traits such as oil, protein, starch and kernel breakage, it may result in more moldy grain.


Field drying

One question is, how much drying will occur in the field as the calendar turns to November?

The amount of field drying can be estimated using growing degree days (GDD) or reference evapotranspiration (RET) values – amount of water a growing plant will transpire. 

It generally takes 30 GDD for each 1% grain moisture reduction from 30% down to 25%, and 45 GDD per 1% of grain moisture reduction from 25% down to 20%, Sanford said. In a typical year, growers can expect 4% drydown in northern Wisconsin to 6% in southern Wisconsin by Nov. 1;  0% to 1% during November; and none in December.

The percentage of drydown based on RET is about 4% for each inch of reference evapotranspiration. The potential field drying is about 0.5% per day in September; early to mid-October it drops to 0.25% per day; mid to late October it drops to 0.125%% per day; and by early November the field drydown rate is only about 0.1% per day. After mid-November very little field drying occurs.

The general recommendation is to start combining corn for dry grain at 25-26% moisture. As the corn gets dryer, combine shatter losses caused by the header increase. The longer the corn is allowed to stand in the field, the higher the losses. A two-year study of field losses of corn left standing after October reported 3%-5% loss in November; 22% in December; and if the corn is allowed to stand in the field all winter, a loss of up to 40%.

In Ohio, research found an average of 11% loss between mid-November and mid-December when corn was left in the field. Thomison’s study was conducted at three locations statewide over a three-year period. It looked at the effects of four plant populations – 24,000, 30,000, 36,000, and 42,000 plants per acre – at three different harvest dates, early to mid-October, November and December – on the agronomic performance of four hybrids in varying maturity and stalk quality.

The Ohio study found:

• Nearly 90% of the yield loss associated with delayed corn harvest occurred when delays extended beyond mid-November.

• Grain moisture decreased nearly 6% between harvest dates in October and November. But delaying harvest after early to mid-November achieved almost no additional grain drying.

• Hybrids with lower stalk strength ratings experienced greater stalk rot, lodging and yield loss with a delayed harvest, while early harvest of the same hybrids eliminated this issue.

• Stalk rot incidence increased the most between harvest dates in October and November, while stalk lodging increased the most after early- to mid-November.


Drying costs

It takes about 0.02 gallons of propane to remove 1% of moisture from a bushel of corn, according to Sanford.

“To estimate drying costs for a high temperature dryer, multiply the propane price by 0.02 and then multiply by the number of percentage points of moisture to be removed,” he said. “For example, if propane is $2.00/gallon and corn is to be dried from 28% to 15% (13%) - $2.00 x 0.02 x 13 = $0.52 drying cost per bushel.”

He provided these tips to reduce drying costs:

• Screen corn before the dryer to remove broken kernels and bees wings so you are only drying salable product

• Use the highest plenum temperature possible without scorching the corn – higher drying temperatures are more energy efficient – less energy required to remove a pound of water.

• Clean screens and air intakes daily so they are free of debris (bees wings, cracked kernels, leaves) to maximize air flow

•  Check gas pressure regulators and burners to ensure efficient and complete combustion before the drying season starts

•   Use dryers with heat recovery or in-bin cooling to reduce the amount of drying needed

 • Prevent condensation under the roof of bins so moisture doesn’t drip back onto the grain. Make sure eaves are open. Adding a ventilation fan to increase air flow under the bin roof may aid in reducing the formation of condensation.

Determining the right drying temperature depends on what the grain will be used for. If corn is being used for feeding or ethanol, the kernel temperature should not get above 140-150°F.

The maximum plenum temperature will depend on the grain moisture and type of drying system being used:

• high-temperature in-bin and batch dryers a maximum plenum temperature of 140 to 150°F is recommended,

• cross-flow dryers are typically 180 to 220°F but if they have multiple stages, the first stage could be higher for higher moisture grains.

•  mixed flow dryers can be operated at higher temperatures because the grain is only exposed to intermittent full plenum heat.

For growers with low temperature dryers, this may be a year when the corn will be too wet to use this type of dryer in many areas, Sanford noted. Corn above 22% may heat or mold before it dries if the bin is loaded in a single fill. Options are to layer corn in small layers to increase the air flow per bushel or install a high temperature heater and dry the corn down to 20-22% with heat (140 to 150°F) and then switch to air-only drying to remove the remaining moisture. This is called combination drying and is one of the most energy efficient and cost effective drying methods.