By Dan Froehlich, Director of Agronomy, The Mosaic Company

Corn harvest has begun at a very slow pace in the cornbelt. Late planted corn, coupled with cooler than normal summer and fall temperatures has delayed harvest and led to frost damage concerns. Grain moisture content at harvest has a significant financial impact on grower profitability. Artificial drying is expensive and can slow down the harvest process, causing higher field losses and handling issues.

Kernel moisture decreases as the kernel develops. Moisture at the dent stage is approximately 55% and drops to 30-35% at physiological maturity (also called black layer). The kernel is safe from a killing frost once it reaches physiological maturity, but still needs time to dry prior to harvest. It takes 25-30 growing degree days (GDD) to lower kernel moisture one point. GDD is the average daily temperature minus 50. A day that had a high temperature of 75 degrees and a low of 65 degrees would accumulate 20 GDD or it would take 1 to 1 ½ days do lower grain moisture 1 percent. As a common rule of thumb, we expect the following dry down rates per day:

When weather conditions are not favorable for rapid grain drydown, hybrid characteristics that influence the rate of grain drying become more important. Traits that tend to increase grain drydown include: husk number, thickness, tightness, and speed of senescence, droopy ears, and smaller cob diameter. High plant populations and taller plants reduce air movement thru the canopy and can slow drydown rate.

Grain moisture content that best minimizes the risks of mechanical damage and harvest loss is near 25%. Most growers prefer to accept some harvest losses and allow the grain to field dry below 22% before beginning harvest. Allowing the corn to field dry longer increases the risk of stalk diseases and lodging so fields need to be closely monitored.