Field drydown of mature corn grain
Delayed maturity of corn due to late planting or simply cool growing seasons often translates into delayed or slow drydown of mature corn grain prior to harvest and, consequently, higher than desired grain moisture contents at harvest. Wetter grain at harvest increases the need for artificially drying the grain after harvest which, in turn, increases the growers' production costs and can delay the progress of harvest itself. Conversely, an early or rapid drydown of the crop decreases growers' costs and facilitates early or at least timely harvest of the crop prior to the colder and, often, wetter conditions of late fall.
click image to zoomFig. 1. Example of field drying progress of a mid-maturity corn hybrid in 2 years with different temperature patterns. Kernel moisture content decreases as the kernels develop through the blister stage (~ 85% moisture), milk stage (~ 80% moisture), dough stage (~ 70% moisture), dent stage (~ 55% moisture), and finally physiological maturity (~ 30% moisture). Prior to physiological maturity, decreases in kernel moisture occur from a combination of actual water loss (evaporation) from the kernel plus the continued accumulation of kernel dry matter via the grain filling process. After physiological maturity (identified by presence of the kernel black layer), percent kernel moisture continues to decrease primarily due to water loss from the kernel.
Weather & Timing of Grain Maturation
Grain moisture loss in the field occurs at a fairly linear rate within a range of grain moisture content from about 40 percent down to 15 to 20 percent, and then tapers off to little or no additional moisture loss after that. The exact rate of field drying varies among hybrids and years. Figure 1 illustrates changes in grain moisture content over time for an adapted medium maturity hybrid in two years with different temperature patterns following physiological maturity.
click image to zoomFig. 2. Average daily grain moisture loss (percentage points/day) relative to average daily air temperature during the drydown period for three corn hybrids planted late April to early May, 1991-1994, westcentral Indiana. Field drying of mature corn grain is influenced primarily by weather factors, especially temperature and humidity/rainfall. Simply put, warmer temperatures and lower humidity encourage rapid field drying of corn grain. Figure 2 illustrates the relationship between the average daily temperature over the entire drydown period and the average daily rate of field drying over the entire drydown period.