Corn Drydown Rates

Choosing the corn moisture content for harvest is often an economic decision that weighs excess harvest losses against the energy costs for drying corn. Other factors, such as stalk strength or the presence of ear rots, should also be considered when determining the target harvest date. Harvesting early may be a good practice since field losses can increase when harvest is delayed, as well as when the crop dries down after maturity. Since energy costs are currently lower than in past years, growers may find it even more advantageous to harvest corn early this season.

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Corn Maturity and Drydown

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When corn reaches physiological maturity or black layer, it is around 30% moisture. There are many factors that can affect how quickly corn dries down in the field after reaching maturity. Warm, dry weather can speed up the drying rate, whereas wet and cool weather can slow it down. Additionally, late-planted and full-season corn products tend to dry more slowly.

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In general, it takes about 30 growing degree units (GDUs) per point of moisture to dry corn from black layer to 25% moisture content1. After reaching maturity, typical drying rates may range from 0.4% to 0.8% loss of moisture content per day2. Rates of drydown vary depending on temperature and moisture levels. Typically, the rate of moisture content loss continues to decrease as temperatures cool and days get shorter. Studies from Purdue University show this relationship, where 0.5% moisture content is lost in a day when the mean GDU accumulation is 12, and 0.75% moisture content is lost in a day when the mean GDU accumulation is 22 (Table 1).

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Knowing the grain moisture content at maturity can help predict grain moisture at different potential harvest dates. A year with wet weather and delays in planting may result in slower field drying of corn. However, if enough growing degree units (GDUs) accumulate, the drying process may be hastened. Other factors may also come into play if harvest is delayed. For example, corn could have developed a shallow root system because of the early-season moisture. In addition, conditions may have been conducive for the development of stalk rots and stalk cannibalization in corn. These factors could lead to higher than normal harvest losses because of an increased risk for stalk lodging in corn this fall. 

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Germplasm Characteristics

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Ear and husk characteristics of different corn germplasm can affect the rate of drydown. These characteristics have the largest effect when weather conditions are unfavorable for rapid grain drying.
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•   Number and Thickness of Husk Leaves. Fewer husk leaves and thinner leaves can lead to faster moisture loss.

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•   Dieback of Husk Leaves. Earlier dieback of husk leaves can lead to more rapid grain drying.

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•   Husk Coverage of the Ear. Husks that are open at the tip of the ear may provide for quicker grain moisture loss.

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•   Tightness of Husk Leaves. Looser fitting husks on the ear can lead to faster grain drying.

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•   Ear Angle. Ears that droop from an upright position after maturity tend to lose moisture more quickly. Upright ears can capture additional moisture from rainfall.

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•  Properties of Kernel Pericarp. Thinner pericarps (outer layer covering a corn kernel) have been associated with faster drying rates in the field.

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Harvest Loss

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The optimum harvest moisture content for corn is approximately 23% to 25%2. At this moisture level, kernels shell easily and stalks generally stand better, which can make harvesting more efficient. A normal harvest loss level of a timely and efficient harvest is about 1 to 2%3. 

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Delaying harvest until corn dries down to 17% to 19% moisture content can save on artificial drying costs. However, as corn dries down in the field there is greater potential for excess harvest losses from stalk lodging and ear drop. Most harvest losses are mechanical, caused by kernel shattering or corn never getting into the combine. Allowing corn to drydown in the field could lead to excess harvest losses, as much as 2 to 8% above the normal level with Table 1. Average rate of grain moisture content loss in relation to average daily heat accumulation. a timely and efficient harvest2.

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If stalk lodging or ear drop problems are observed, harvest timing will be more critical to maximize yield potential. Time should be taken to watch crop condition in the field in an effort to balance field drydown with harvest losses.

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