Defining Corn Relative Maturity (CRM)

There can be a lot of confusion when it comes to corn maturity and company published numbers.  Typically, most folks in the industry converse about “days”.  I often hear from a customer, “I have Pioneer 83 day planted in the Home Half”.  Or, “91 day” or “85 day”, etc.  Well, that “83” number is actually the company’s published designated Corn Relative Maturity (CRM) for a stated hybrid.  The grain CRM for a corn hybrid is defined within Pioneer® as the maturity it takes for a hybrid to progress from planting through the season and ending at a “harvestable moisture” content under average conditions.  The CRM designation has nothing to do with a number of days to maturity, but is more related to growing degree (heat) unit accrual.

Each new hybrid coming along through a corn breeding program is measured against some very well-known benchmark hybrids to determine the relative maturity (RM) rating.  Researchers typically gain 6-7 seasons of data accumulation on a hybrid before it reaches commercial designation so the database is a robust set of observations at various locations to accurately designate a RM value.  “Harvestable moisture” obviously will vary from year to year based on weather, but more important is to remember an individual hybrid will vary in its grain drydown rate as well and this is factored into the CRM rating.

For grain RM designation, each individual RM score reflects about a 0.5 point moisture advantage.  Therefore, if you are comparing two hybrids from Pioneer® (planted and harvested on the same day), and one is designated at 79 RM and the other at 83 RM, there should be approximately 2 full points of grain moisture difference at harvest for maturity.

Many seed companies will publish a “physiological RM” (or black layer RM) which designates the maturity from planting to full physiological maturity.  Black layer will typically occur around 30-35% grain moisture content and thus this designation cannot take drydown into account.

If you are a corn silage producer, you need to inquire with your seed representative about “Corn Silage RM”.  This silage RM is defined within Pioneer® as the maturity from planting to 65% whole plant moisture, or the timing needed for optimum silage harvest to occur for ideal conditions around storage, feed quality, etc.  For silage RM, each one day difference between two hybrids (planted and harvested on the same day) will result in about a ¾ point moisture difference at cutting time.  It is very common to potentially have a 4-8 RM difference between grain CRM and corn silage RM.

Also in the Pioneer seed brochure, you will also notice a corn “Silking RM”, which is a rating of maturity from planting to first silk formation (may also be referenced as “Flower RM” from other companies but is slightly different as “flower” in corn refers to the tassel).  For those of you that may like to push longer maturities in your local environment, you should evaluate this number as hybrids that silk earlier compared to their stated grain RM tend to move north in our geography more effectively.

Lastly, please remember these definitions are for the Pioneer® brand and are not industry standard.  Each of the various seed companies in the industry could and does rate their products differently and I wouldn’t be surprised if you have experienced unexpected variability in this regard.