Select the right corn maturity for your growing area
One of the most important decisions you make each year is what corn variety to plant. Same as the previous year? Shorter day? Longer day? What type of corn are you going to grow? BMR? Dual-purpose? Grain? Silage?
Other attributes to consider are standability, disease and insect resistance, ear and kernel size, lodging, hybrid response to management, and the list can go on. The decision on what to plant will vary from farm to farm, depending on the operation and its needs. The performance of this year’s corn crop will also likely influence your decision for next year’s growing season.
Different systems can be used to classify corn hybrids, such as relative maturity (RM) or growing degree days (GDD; also referred to as growing degree units (GDU)).
The figure shown here is the Wisconsin RM zone map (Source: University of Wisconsin-Madison Department of Agronomy). Each state will have a similar RM map. RM is a relative measure for a given hybrid compared to hybrids of known maturity expressed in days (does not represent the number of days required from emergence to physiological maturity). Within each region on the RM zone map, it shows what hybrids do best in those regions.
GDD systems classify hybrid GDD requirements with the number of GDD that typically occur during the growing season for a given location and planting date. GDD can be calculated based on maximum and minimum air temperatures.
When the maximum air temperature is greater than 86 degrees F, the value is set to 86 degrees F as the growth rate of corn does not increase beyond 86 degrees F. The same concept applies to minimum temperature as well. When the minimum is less than 50 degrees F, the minimum value is set to 50 degrees F.
A base line of GDD required for corn emergence is roughly 125 GDD. Factors that can influence approximate GDD for corn to emerge include adequate soil moisture, planting depth, tillage system and residue cover.
Another consideration when selecting corn hybrids and RM is when the first frost typically occurs in the fall, although this date is a moving target. The map to the right shows average first frost in Wisconsin (Source: UW-Madison Department of Agronomy). If the selected hybrid is for grain, you should reach maturity at least 10 days before the first frost as this allows time for grain dry-down prior to harvest.
Selecting hybrids for corn silage will depend on whether you are planting specifically for silage or dual-purpose corn. When looking at silage type, you should consider the following factors: Yields, digestibility, fiber levels, stover, feed requirements, harvest timing and soil conditions at harvest time.
When selecting corn based on RM or GDD, choose a variety that best fits your area and perhaps has worked for you or a nearby peer in the past. Your agronomist can help in this decision. You want to choose the best option for your operation that will be profitable for you in the end.