Corn Maturity and Drydown

Corn kernels are around 30% moisture content when physiological maturity or black layer occurs. Several factors influence field drydown after maturity. Kernel moisture content decreases faster with warm, dry weather and may decrease slowly in a wet and cool environment.

Fuller season corn products, that require more growing degree units (GDUs) to mature, will likely be slower drying as the fall progresses within an area. Crop maturity can be hastened by dry weather conditions, which usually results in a loss of yield potential because plant death occurs before the kernels gain their full weight and size.

Typical drying rates after black layer range from 0.4% to 0.8% kernel moisture content loss per day.1 About 30 GDUs per point of moisture are required to dry corn from black layer to 25% moisture content.2 Purdue University studies showed that a loss of 0.5% moisture content occurs when the mean accumulation of GDUs is 12, and 0.75% moisture content is lost when the mean accumulation of GDUs is 22 per day respectively. University of Minnesota research indicates field drying rates decline during September and October (Table 1).

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 loss.
  • Husk Tightness. Husks that are loose and open may help increase grain drying.
  • Ear Angle. Drooping ears tend to lose moisture more quickly. Upright ears can capture moisture from rainfall.
  • Kernel Pericarp Properties. Thinner pericarps (outer layer covering a corn kernel) have been associated with faster field drying rates.

Late-planted corn can result in taller plants, smaller diameter stalks, pollination when temperatures are hotter, and delayed maturation. Delayed maturation can result in a less than desirable grain moisture content well into the harvest season. Cooler fall temperatures decrease the rate that kernels lose moisture content. More importantly, an early frost can be a threat for late-planted corn or timely planted corn that experienced a cooler than expected growing season. A cool growing season in combination with late planting can push maturation into potential frost time frames (Table 2).

The maturity of most corn products is based on GDUs required to reach black layer. Based on planting date, growing season temperatures, and the GDU maturity date for a product, an approximate calendar maturity date can be calculated for a corn product. This information can be used to help schedule harvest, marketing of grain, and determining if drying will be required. The calendar date calculation can also be used to help determine if the product has an opportunity to mature before typical area frost dates.

To calculate GDU and corn growth stage go to NDAWN.

Date % Grain Moisture Content Loss per Day
September 15 - 25 0.75 - 1.00
September 26 - October 5 0.50 - 0.75
October 6 - 15 0.25 - 0.50
October 16 - 31 0.00 - 0.33
After October 31 Very little

Source:Table 1. Field drying rates for corn in Minnesota.Source: Coulter, J. 2008. Maturity, frost, and harvest moisture considerations for corn. University of Minnesota.

Corn stage Days to maturity % Yield loss frost to leaves only % Yield loss frost to leaves/stalks % Grain moisture
Early dent 25 25 32-40 59
Dent 19-22 12 23 51
Late dent 10-15 8 15 47
Half-milk 5 5 8-12 40
Maturity 0 0 0 28-35

Source:Table 2. Reductions in corn yield due to frost. Coulter, J. 2008. Maturity, frost, and harvest moisture considerations for corn. University of Minnesota.