Corn Maturation and Drydown Less than 100 RM

  • Corn kernels are around 30% moisture content when physiological maturity occurs.

  • A cool growing season in combination with late planting can push harvest later into the fall.

  • Cooler fall temperatures decrease the rate that the kernels lose moisture content.

  • Delayed maturation can result in a less than desirable grain moisture content at harvest time.

Corn Maturity and Drydown

 
Figure 1. Black layer at kernel tip.  

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

  • Number and Thickness of Husk Leaves. Fewer husk leaves and thinner leaves can lead to faster moisture loss.

  • Husk Dieback. Earlier dieback of husk leaves can lead to more rapid grain drying.

  • Ear Tip Exposure. Exposed ear tips may provide for quicker grain moisture loss.

  • Husk Tightness. Husks that are loose and open may help increase grain drying.

  • Ear Angle. Drooping ears tend to lose moisture more quickly. Upright ears can capture moisture from rainfall.

  • Kernel Pericarp Properties. Thinner pericarps (outer layer covering a corn kernel) have been associated with faster field drying rates.

Table 1. Average rate of grain moisture content loss in relation to growing degree unit (GDU) accumulation.*
Mean Daily GDU Accumulation During Drydown
% Grain Moisture Content Loss per Day
12
0.5
17
0.6
22
0.75
*Three corn products planted in late April to early May, 1991-1994 in west central Indiana (Purdue University Agronomy Research Center). Source: Nielsen, B. 2001. Post-maturity grain drydown in the field. Agronomy Tips. Pest & Crop. Purdue University. http://extension.entm.purdue.edu
 
 

Late Planting and Cool Weather

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.

 

Frost Potential

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.

 

Maturity Calculation

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:

http://ipcm.wisc.edu/blog/2013/08/new-android-app-crop-calculators-for-corn/

The University of Vermont offers an Excel-based calculator:

http://pss.uvm.edu/vtcrops/CompProg/GDDCalculator.xls

South Dakota State University offers a web-based calculator:

http://climate.sdstate.edu/awdn/archive/degreedays.asp

Michigan State University offers weather based pest, natural resource, and production management tools online at:

http://enviroweather.msu.edu/

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.

http://www.yourweekendview.com/outlook/agriculture/growing-degree-days/

 

Table 2. Required GDU and date when growth stage is theoretically achieved for a 95-105 RM corn product planted May 1 in southern Wisconsin.
Growth Stage
Required GDU
Date
Average
Range
VE
125
May 12
May 10-14
V6
470
June 7
June 5-9
V12
815
June 26
June 22-29
V18
1160
July 13
July 9-18
R1
1250
July 17
July 13-20
R6
2350
Sept 11
Sept 4-19
Source: Lauer, J. 2014. Corn development. Corn Agronomy. University of Wisconsin. http://corn.agronomy.wisc.edu
 

Table 3. Estimated accumulated GDUs required for 80-95 RM corn.
Growth Stage
80 RM
95 RM
Emergence (VE)
110
110
Silk (R1)
1100
1250
Physiological Maturity (R6)
1900
2200
Source: Best management practices for corn production in South Dakota. EC929. 2009. South Dakota State University.