Corn School: What Does a “Day” Really Mean in Regards to Corn?

When a growing season doesn’t go exactly as hoped — a late spring, a cool summer, too much rain — corn growers get understandably nervous. Corn is a C4 plant — it can tolerate hot weather and needs rather warm weather to grow, set yield and mature. As much of Ontario deals with “weird and whacky” weather this growing season, farmers have one eye on the field and one on the calendar, tallying up the days the crop needs to make it to maximum yield.

Which brings us to the topic of this audio-only Corn School episode. Unlike some other crops, hybrids are sometimes rated according to the number of “days” it takes to mature. Real Agriculture readers asked, “What does a day mean for corn?” To answer that, we asked Dr. Dave Hooker, associate professor and agronomist, with the University of Guelph, Ridgetown campus.

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“There are actually three ways to express corn maturity ratings,” says Hooker, each system with its own pros and cons. In the interview below, Hooker recaps the three terms farmers will see when comparing corn varieties and what they really mean. Following that, Hooker explains how corn compensates for missing heat units and bad weather, and when a longer-season hybrid grown during a cooler or abbreviated summer (i.e. early frost) gives up yield potential, which brings us to a discussion on the importance of potentially changing hybrid maturities in a late planting season.

As a general rule of thumb, Hooker adds, you can take a “day” and multiply it by 30 to get a rough estimate of the heat units a variety needs to finish.

If you can’t see the embedded player, click here to hear this interview.


RealAgriculture Agronomy Team

A team effort of RealAgriculture videographers and editorial staff to make sure that you have the latest in agronomy information for your farm.


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