- Kernel drying that occurs following black layer is entirely due to evaporative moisture loss.
- Corn dry down rate is tightly linked to daily growing degree unit (GDU) accumulation.
- In general, drying corn from 30% down to 25% moisture requires about 30 GDUs per point.
- Drying from 25% to 20% requires about 45 GDUs per point (Lauer, 2016).
- GDU accumulation and dry down rates are greatest during the earlier, warmer part of the harvest season and decline as the weather gets colder (Table 2 and Table 3).
- By November, GDU accumulation rates are low enough that little further drying will typically occur.
Table 2. Average daily GDU accumulation during early-, mid-, and late-September and October for several Midwestern locations (1981-2010 average, Midwest Regional Climate Center).
Table 3. Average daily corn dry down rate for difference stages of the harvest season (Hicks, 2004).
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.
Weather Conditions Following Maturity
- Daily GDU accumulation and dry down 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.
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 dry down 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 dry down.
- Kernel pericarp characteristics – Thinner or more permeable pericarp layers are associated with a faster dry down rate.