This year was one of the most difficult, cold, wet and long planting seasons I can remember. Just when I think I’ve seen it all, Mother Nature pulls some new combination of temperature and rain out of her bag. We could have used some “global warming” this spring!
We need more heat to mature very late-planted corn. Most growers know that corn growth is driven by heat units or growing degrees days. The maximum GDDs available in a growing season at any location are counted from March 1. So with later plantings, you lose a certain number of GDDs for the season before you even plant.
Growers in the northern Corn Belt use corn hybrids with earlier than 100-day relative maturity. Growers in most of the central Corn Belt use hybrids that range in relative maturity from 105 to 115 days. They require 2,400 to 2,800 GDDs to mature.
How do you calculate GDDs? Subtract 50 from the average daily temperature to get the GDDs for each day, with the limitation that if the low temperature falls below 50 degrees F, use 50 as the low temperature, and if the temperature goes above 86 degrees, use 86 as the high for that day. Corn does not grow when temperatures are below 50 degrees, and above 86 degrees, corn plants are under stress and appear to shut down. Of course, the availability of moisture during heat stress may be helpful in corn growth and maturity.
If you add the GDDs of each day from planting to black layer or physiologic maturity, you get the growing degree days needed by the hybrid.
Relative maturity of a hybrid is not a constant number. That’s why it is called “relative” and is affected somewhat by the planting date. In the central Corn Belt, if you plant corn after May 10, the GDDs needed by the typical hybrid to reach physiologic maturity are reduced. As we know, a black layer is formed at the tip of the kernel at physiologic maturity, after which no more dry matter goes into the kernels and the process of dry matter accumulation comes to a halt.
Mother Nature’s trick
Bob Nielsen of Purdue University Extension and Peter Thomison of Ohio State University Extension discovered that late-planted corn requires about 200 fewer GDDs to reach maturity than earlier-planted corn of the same hybrid. The exact reason for this is not known.
I think it may have to do with the survival of the species in an evolutionary sense. Can plants detect from day length that they need to speed up the process of maturity if their seed is going to become fully mature? They want to produce mature seed even though it may be smaller. Of course, that tends to reduce yield of later-planted corn.
Whether late-planted corn will mature before the killing frost will depend on temperatures in August and September. October generally contributes little to crop maturity. Let’s hope for a warmer summer and fall so we can harvest fully mature crops with lower grain moistures!
Nanda is president of Agronomic Crops Consultants LLC. Email him at firstname.lastname@example.org, or call him at 317-910-9876.