By Roger Elmore and Lori Abendroth
13 Sep 2007 -
Corn is physiologically mature (R6) or nearly so in many areas of Iowa for early planted corn. Corn that is mature will have a “black layer” that appears at the base of the kernel. The appearance of this black layer designates the end of dry matter accumulation. Although corn is harvested at high grain moistures for silage and seed corn, ideal harvest moistures for field corn range from 15 to 20%.
Delaying harvest until corn dries to approximately those levels will save considerable artificial drying costs. Yet as corn dries, hybrids and fields with poor stalk quality become increasingly susceptible to stalk lodging. Harvest efficiency will decrease rapidly and harvest losses will increase in fields with downed corn. The 10 Sept 2007 Iowa Crops & Weather report indicates that 15% of Iowa’s corn is either moderately or heavily lodged (USDA, NASS). When will it be possible to harvest these problematic fields?
At what speed does corn dry down after reaching maturity (R6)? Several factors impact the rate of dry down: weather, hybrid, planting date, and ear characteristics. On average, typical seasonal drying rates range from 0.4 to 0.8% moisture loss per day. If the fall months vary from normal in terms of temperature or moisture, the rate of dry down will differ. For example, wet and cool weather will delay drying. We’ve recorded seasonal dry down rates less than 0.3 % per day. On the other hand, warm dry weather speeds drying rates. Kernels could lose up to 1.0% moisture per day. Considering that corn at maturity has about 30% moisture content it could easily take 2 to 4 weeks for grain moisture to drop to 15%.
Hybrids will vary in rate of dry down as well. Drying rates of later maturing hybrids or late-planted corn are slower than earlier maturing hybrids or early-planted corn. This is partly because the corn matures when days are shorter in length and temperatures are usually cooler.
Husk and ear characteristics will also affect dry down. Ears with the following will allow for faster drying: fewer and thinner husk leaves; early husk leaf senescence; ears with tips that protrude beyond the husks; looser husk leaves; early ear drop from an upright position; thinner or more permeable pericarp. Dr. Bob Nielsen at Purdue University has a more complete discussion of this at: http://www.kingcorn.org/news/articles.05/GrainDrying-0815.html