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Corn kernels are around 30% moisture content when physiological maturity or black layer occurs (Figure 1). 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 (Table 1).
Corn products differ from one another in drydown rates. Plant characteristics that can influence drydown rate include:3
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 in some parts of the United States can push maturation into potential frost time frames.
The maturity of most corn products is based on the amount of 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 harvesting, marketing of grain, and determining if extra fuel may be required for bin drying. The calendar date calculation can also be used to help determine if the product has an opportunity to mature before typical area frost dates.
Some universities provide corn maturity calculators. By entering a location, planting date, and the GDUs to silk or black layer, a maturity date is then estimated. A variety of resources are available:
The University of Wisconsin offers a calculator for your Android mobile device at the following site:
The University of Vermont offers an Excel-based calculator:
South Dakota State University offers a web-based calculator:
Michigan State University offers weather based pest, natural resource, and production management tools online at:
A growing degree day calculator can also be found on The Weather Channel website, weather.com, for all locations. The accumulated growing degree days can be compared to the amount needed for the corn product planted.