Persistent rainfall across much of the Corn Belt have slowed both field operations and natural corn grain drydown this fall. As farmers evaluate harvest timing, the Iowa State University Corn Drydown Calculator can help estimate how quickly grain moisture will decline and support harvest scheduling decisions. The tool was originally developed to predict corn drydown after physiological maturity (R6; approximately 30−35% grain moisture) and has recently been enhanced with expanded geographic coverage and additional scenario options.
The Corn Drydown Calculator allows users to select a field location, enter a date, and input known grain moisture. The date can be any day after physiological maturity (e.g., Oct 2nd) and next to it add the grain moisture content on that day (e.g., 30%). The tool then estimates how grain moisture will change over time using weather-based calculations of the atmosphere's drying potential. Research conducted near Ames has shown that grain drydown rates can vary considerably depending on weather conditions and timing after physiological maturity. Typical drydown rates often range from about 0.4 to 0.8 percentage points per day under favorable fall conditions, in warm, dry weather. On the other hand, cool temperatures and high humidity or rainfall can slow drying substantially to rates below 0.3 percentage a day.
A key enhancement to the updated tool is the ability to compare up to three scenarios. Users can evaluate grain drydown using a median weather year, the current year with weather forecasts, and an analog year of their choosing as the initial default scenarios. These options provide a range of possible outcomes and help users understand how weather conditions may influence the number of days needed to reach a desired harvest moisture.
The calculator is not intended to replace field scouting or assessments of stalk quality. Fields with compromised stalk integrity, stalk rots, lodging potential, or ear droppage concerns may warrant earlier harvest even if grain moisture remains above the desired harvest moisture. However, for fields with acceptable standability, the tool can help farmers prioritize harvest order, estimate drying costs, coordinate labor and equipment needs, and make more informed harvest management decisions.
In the coming weeks, the Corn Drydown Calculator will be updated with new functionality to be used to link planting decisions (e.g., planting date and hybrid maturity selection) to harvest implications. The updated version will be available in the coming weeks and will be accompanied with an announcement.
Figure 1: Example of Corn Drydown Tool being used to estimate drydown timing for a corn field in Dallas County, IA. The corn on Oct 2nd had 30% grain moisture. The tool predicts grain moisture will drop to 20% by Oct 15. For reference, at the same location, it took longer to reach 20% moisture in 2018 (Oct 21) and less time in 2014 (Oct 13).
Link to the tool: https://facts.extension.iastate.edu/corn-drydown-calculator
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- Extension Cropping Systems Specialist
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- Integrated Cropping Systems
- Postdoc Research Associate