This year’s early frost could make drying corn more difficult.

The corn’s moisture content likely will vary greatly, according to Ken Hellevang, North Dakota State University Extension Service grain drying expert.

“The first step is to determine the corn’s maturity and expected harvest condition,” he advises.

For example, corn just in the dough stage contains about 70 percent moisture, while in the dent stage, the moisture content is about 60 percent. The moisture content is about 52 percent in corn at the 75 percent milk stage, 40 percent at the 50 percent milk stage, 37 percent at the 25 milk stage and 32 percent if the corn is mature.

As of Sept. 18, three days after the first major frost in North Dakota this year, 83 percent of the state’s corn crop was dented, and 20 percent of that was mature, the National Agricultural Statistics Service’s North Dakota field office reports. That means 17 percent of the crop did not reach the dent stage before frost ended the corn growing season.

The amount of drying in the field will depend on parameters such as corn maturity, hybrid, moisture content, air temperature, relative humidity, solar radiation and wind speed. The moisture content to which corn will dry is determined by the corn’s equilibrium moisture content, which is based on air temperature and relative humidity.

Potential evapotranspiration (PET) is one predictor of corn’s drying rate. Evapotranspiration is the transfer of water from the Earth’s land surface and plants to the atmosphere. PET is based on parameters similar to those that affect drying.

Standing corn in a field may dry about 0.5 to 0.7 percentage point per day during September, 0.3 to 0.5 percentage point per day during October and 0.15 to 0.2 percentage point or less per day in November under normal weather conditions.

This means corn at 40 percent moisture content on Sept. 15 could be expected to dry to about 31 percent by Oct. 1 and 20 percent by Nov. 1 However, corn at 60 percent moisture content on Sept. 15 might dry to only about 50 percent by Oct. 1, 40 percent by Nov. 1 and 35 percent by Dec. 1.

Immature corn may dry more slowly in the field than mature corn, and frosted high-moisture corn can mold on the stalk.

“Therefore, field drying normally is more economical until mid to late October, and mechanical high-temperature drying normally is more economical after that,” Hellevang says.

Some producers leave corn on the field through winter to reduce the drying cost, particularly light test weight corn having moisture contents exceeding 30 percent in the fall. However, field drying is extremely slow during the winter, with corn drying to only about 20 percent moisture content by late February or early March.

Corn that isn’t harvested until late spring can be expected to dry to 14 to 16 percent moisture content.

Hellevang recommends producers examine and push on the corn stalks to determine their condition before deciding to leave corn standing in the field through winter. Corn losses generally have been small if the corn stalks were strong in November. However, frosted corn typically has weaker stalks, so field losses could be greater this year than in previous years.

Other disadvantages of leaving corn standing in fields during the winter include wildlife feeding on the corn, which can result in large losses, and accumulated snow and the cover the corn provides can result in wet fields in the spring.

For more information about corn drying, visit NDSU’s grain drying website at http://www.ag.ndsu.edu/extension-aben/post-harvest.

NDSU Agriculture Communication - Sept. 26, 2011