Corn Maturity and Drydown (North Central Corn Belt)

Moisture Loss During Grain Fill

  • Kernels lose moisture through the grain filling period due to a combination of evaporative water loss and accumulation of kernel dry matter.
  • Corn plants channel photosynthate into the kernels during the grain fill period, increasing kernel dry weight.
Kernel moisture during kernel growth stages

R. L. Nielsen, 2001

Physiological Maturity

  • Maturity signified by the formation of an abscission layer or "black layer" at the base of the kernel.
  • The black layer forms when the hard starch layer reaches the base of the kernel.
  • Kernel dry weight does not increase after this point.

Cross section of kernels at physiological maturity. The black abscission layer is visible at the tip of the kernels.


Drydown Following Maturity

  • Kernel drying that occurs following black layer is entirely due to evaporative moisture loss.
  • Drydown rates are greatest during the earlier, warmer part of the harvest season and decline as the weather gets colder.
  • By November, little further drying will occur.

Moisture Loss Per Day Under Favorable Conditions

Moisture Loss Per Day Under Favorable Conditions

D. R. Hicks, 2004

Factors that Influence Corn Drydown Rate

1. Timing of Physiological Maturity

  • Corn that matures earlier will dry down faster due to more favorable drying conditions early in the harvest season.
  • Later maturing corn has fewer warm days to aid in drying, and will dry down at a slower rate.
Days to 25% moisture and 25% moisture based on maturity date.

Data derived from D. R. Hicks, 2004

2. Weather Conditions Following Maturity

  • Corn drydown rate is tightly linked to daily growing degree unit (GDU) accumulation.
  • GDU accumulation can vary widely during the harvest season.
  • Corn may dry 1 point of moisture per day or more under favorable conditions.
  • Conversely, corn may not dry at all on a cool, rainy day.

Corn drydown rates may differ dramatically between a warm, dry fall vs. a cool, wet fall.

GDU Accumulation in Mankato, MN (2004 - 2008)

Accumulation in Mankato

Data from Pioneer website.

Simulated drydown rates for corn maturing on Sept. 15, based on historical GDU data for Mankato, MN*


* Assumes 20 GDUs = 1 point drop in moisture

3. Hybrid Characteristics Affecting Drydown

  • Husk leaf coverage – The more insulated the ear is, the longer it will take to dry down. Leaf number, thickness, and tightness all affect drydown rate.
  • Husk leaf senescence – the sooner these leaves die, the faster the grain will dry down.
  • Ear angle – Upright ears are more prone to capture moisture in the husks which slows drydown.
  • Kernel pericarp characteristics – Thinner or more permeable pericarp layers are associated with a faster drydown rate.

Two hybrids that differ by one day of relative maturity will usually differ by 1/2 point of moisture if planted on the same day.


Coulter, J. 2008. Maturity, Frost, and Harvest Moisture Considerations for Corn. Univ. of Minnesota.

Hicks, D.R. 2004. The Corn Crop – Frost and Maturity. Univ. of Minnesota

Nielsen, R.L. 2000. Field Drydown of Mature Corn Grain. Purdue Univ.

Nielsen, R. L. 2001. Grain Fill Stages in Corn. Purdue Univ.

Thomison, P. 2004. Corn Drydown. Ohio State Univ.