Rate of dry down in corn before harvest

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The latest USDA-National Agricultural Statistics Service crop progress and condition report classified more than 50% of the corn crop to in good or excellent condition. Overall, 75% of Kansas’ corn is mature with only 29% harvested.

The weather conditions experienced from mid-August to mid-September were critical for corn as related to the grain filling rate and determining final grain weight. Temperatures and precipitation were split across the state, with warmer-than-normal conditions in the northwest and cooler conditions in the southeast.  There was a small area of east central Kansas that had excessive moisture but much of the state had less than half of the normal precipitation for the period (Figure 1).

Figure 1. a) Departure from normal temperatures; b) percent of normal precipitation.

In recent years, a common question from producers is related to the dry down rate for corn when approaching the end of the season. Based on previous information, the average dry down rate depends on the weather, primarily temperature and moisture conditions – but it might range from 1% in late August to less than 0.5% per day in October.  The weather outlook for October calls for an increase chance of warmer-than-normal temperatures with equal chances for above- or below-normal precipitation.  This would favor a faster dry down rate than average.

According to a recent Extension article from Iowa State, “Corn grain dry down in field from maturity to harvest”, grain water loss occurs at different rates but with two distinct phases: 1) before “black layer” or maturity (Figure 2), and 2) after black layer. For the first phase, Table 1 contains information on changes in grain moisture from dent until maturity of the corn.


Figure 2. Corn at dent stage and at black layer growth stages. Photo and infographic prepared by Ignacio Ciampitti, K-State Research and Extension.


Table 1. Growth stages, moisture content, and total dry matter progression for corn from late to physiological maturity. Extracted from K-State Research and Extension publication MF3305 (Ciampitti, Elmore, Lauer, 2016).


In order to properly address the rate of dry down question from many of our producers, a study was conducted to investigate the effect of the grain dry down rate from the moment of “black layer” until commercial harvest grain moisture is reached. For the conditions experienced in 2017 (from late August until mid-September), the overall dry down rate was around 1% per day (from 35% to 13% grain moisture) – taking an overall period of 23 days.


Figure 3. Grain moisture dry down (orange line) across three hybrids and different N rates near Manhattan, KS. Horizontal dashed lines marked the 35% grain moisture at black layer formation and 13% grain moisture around harvest time*. Graph prepared by Ignacio Ciampitti, K-State Research and Extension.

*Note: It is desired to reach harvest with 15.5% grain moisture to maximize the final grain volume to be sold, thus the importance of timing harvest with the right grain moisture content.

This dry down process can be delayed by:

  • Low temperatures
  • High humidity
  • High grain moisture content at black layer (38-40%)


It is expected that the dry down rate will decrease to <0.5% per day for late-planted corn entering reproductive stages later in the growing season. A similar decrease is also expected for corn that was exposed to late-season stress conditions (e.g., drought, heat). Under these conditions, maturity may be reached with high grain water content and the last stages after black layer formation could face lower temperatures and higher humidity. These main factors should be considered when the time comes to schedule corn harvest.

This project is expected to be expanded in the coming years to include additional corn producing regions and to consider other factors such as planting date, hybrid maturity, and diverse weather environments across the state. If you are interested in participating, please contact the researchers listed below.



Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist

Javier Fernandez, Fulbright Scholar, KSUCROPS Production, Dr. Ciampitti’s Lab

Mary Knapp, Weather Data Library