Hybrid Maturities

Corn hybrid maturity ratings can be confusing to farmers and Ag professionals. One of the causes for this is that maturity can mean different things to different people.

Agronomists and plant breeders talk about corn maturity and think about the end of the grain fill period. This is the point when kernel weight has reached its highest point for the crop. Another term that is used interchangeably is “physiological maturity”. Another term that may be more commonly used is to say the crop has reached “black layer”, because an actual black layer develops at the tip of the kernel.

Grain moisture at this stage can be anywhere from 25 to 40%, and is typically in the mid 30%. It varies from hybrid to hybrid and year to year because of growing conditions in the season.

Most growers think of maturity in terms of “harvest maturity”, or when the crop can be harvested with minimal kernel loss or damage, and minimal drying expense. Usually growers like to see this harvest moisture around 25% or lower, depending upon whether the crop will be stored and fed for high moisture grain or marketed as dry grain.

Traditionally corn hybrids have been rated by seed companies on days to maturity, such as a 98 day hybrid for example. This method of rating hybrid maturities compares new hybrids to other hybrids of known maturity based on their grain moisture content at harvest time. The normal standards are that a hybrid will have a dry down rate of about 0.5 percentage points per day, so if the new hybrid has grain moisture 4% over a known hybrid that is rated as a 90 day hybrid, the new product would be rated as a 98 day hybrid (4 points moisture divided by 0.5 points per day moisture loss equals 8 days). It’s important to keep in mind that this system uses some assumptions about average grain drydown and normal growing conditions, as we well know from this last season, not all years are normal growing seasons.

Another method used to express relative maturities considers heat units, often referred to as growing degree days, or growing degree units. This method takes into consideration the amount of heat accumulated of a specific period of time. It is based on actual temperature measurements and not based on comparisons to other hybrids. Trelay has corn hybrids that range from 2150 to 2925 growing degree units in our product line-up.

The correlation between the two systems is close but not identical. Neither method is perfect because they are influenced by the environmental factors of the growing season, and plant stress on plant maturation such as moisture and or drought as a couple examples. Another factor to keep in mind is that not all seed companies use the same method for hybrid maturity evaluations. Some count days from planting, and some count days from crop emergence, so there can be some variation between two seed companies that are both selling products that are marketed as 98 day hybrids.

So what does this all mean to you? This is just one more reason you need to do some research before making decisions on hybrids. Be careful not to make decisions based on a single plot or test location. The more plots and yield info that you can compare across several sites and multiple years will give you a much better idea of how a specific hybrid will perform on your farm. Your local Trelay Rep will be able to help supply you with much of this information to partner with you and help make the best decision for your farm.