Corn Drydown

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When is corn going to mature and when will it be dry enough to allow for harvest? Several factors can influence field drydown of corn grain after maturity, including weather conditions and seed product characteristics.

Corn kernels are around 30% moisture when physiological maturity or black layer occurs (Figure 1). How quickly corn will drydown after maturity will dictate harvest date and the amount of on-farm drying that will be needed. Depending on the conditions, post black layer corn may need a month of field drying to reach a moisture content that facilitates an efficient grain harvest.

 

Figure 1. Black layer at kernel tip indicates that corn has reached physiological maturity.

The actual rate of drying will be influenced by the moisture of the corn and weather factors such as temperature, relative humidity, and wind speed. Kernel moisture content decreases faster with warm, dry weather. Cooler fall temperatures decrease the rate that kernels lose moisture content. Fuller season corn products will also be more likely to drydown slower as the fall progresses within an area.

 

Figure 2. Field drydown of corn showing a husk covered ear on the left and a drooping, open husk on the right. Which corn ear will likely have faster drydown in the field?

The ideal harvest moisture content for corn is considered to be around 23 to 25%. At this moisture, kernels shell easily and stalks generally stand better, which can make harvesting more efficient. Corn drydown is linked to growing degree units (GDUs). Under ideal weather conditions, corn could lose up to one point of moisture per day. However, studies have shown that typical drying rates after black layer can range from 0.4% to 0.8% kernel moisture content loss per day.1 As the days get cooler, GDU accumulation per day decreases and grain drying slows. As a rule of thumb, 30 GDUs per moisture content point are required to lower the grain moisture content from 30 to 25%, and 45 GDUs per point are required from 25 to 20%.2 This means that late-maturing corn may take two to three times longer to dry in the field.

Field losses can increase as drydown occurs in the field. Combine losses are least when corn is around 25% moisture and increases as grain dries. Losses can be as high as 10 to 15% when grain is harvested at 15% moisture.

Corn products differ from one another in drydown rates. Plant characteristics that can influence drydown rate include:3

  • Number and Thickness of Husk Leaves - fewer husk leaves and thinner leaves can lead to faster moisture loss.
  • Husk Dieback - earlier dieback of husk leaves can lead to more rapid grain drying.
  • Ear Tip Exposure - exposed ear tips may provide for quicker grain moisture content loss.
  • Husk Tightness - Husks that are loose and open may help increase grain drying (Figure 2).
  • Ear Angle - Drooping ears tend to lose moisture content more quickly (Figure 2).
  • Kernel Pericarp Properties - Thinner pericarps (outer layer covering a corn kernel) have been associated with faster field drying rates.

Waiting for corn grain to dry to 18% moisture or less in the field can certainly save on the energy bill, but it also increases the likelihood of excess harvest losses due to stalk lodging, ear drop, and detrimental weather, all of which can affect your bottom line.

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