Heat, High Yields and Hybrid Selection
Corn and Heat
Heat: it's what almost anyone
involved in the corn industry says it takes to grow a good crop of corn. Corn
physiologist Prof. Thys Tollenaar of the Department of Plant Agriculture at
the University of Guelph believes the ideal growing season for corn in Ontario
requires above-average temperatures in the beginning and end of the season
but with normal- to below-normal temperatures during the middle of the growing
season. The principles at work here are fairly straight forward. First, our
short season demands that for maximum productivity we get our corn off to
a fast start, to create a plant canopy that will maximize sunlight interception.
Second, excessive heat during the middle of the season can often create yield-limiting
stresses, especially if soil moisture is low. Finally, a warm end-of-season
allows grain filling to occur more efficiently and allows for more acceptable
grain harvest moistures. Considering these factors, 1998 may have been one
of the finest corn growing seasons that we have yet experienced in Ontario...even
though we had some frost and drought.
Early Season Advantage
Last year provided an abnormally high heat unit accumulation in
May and June. Table 1 outlines Ontario Corn Heat Unit (OCHU) accumulation
at three sites across the province and points to the pattern that generally
across the province heat unit accumulation was 20- to 30-per cent above normal
by June 30. Early heat drives soil temperatures up which in turn drives germination,
root growth and leaf development. Early planted corn in 1998 generally had
a significant canopy developed by mid-June and was intercepting that intensive
late June sunlight that often eludes us in seasons when early growth is delayed
by cool temperatures in May.
Hot Air in Ottawa
1 - Early season heat unit accumulation
Heat Units accumulated by June 30. (1998)
Heat Units accumulated by June 30. (30-year normal)
The yields from many sites across the province were impressive this year. But
the high yield results from the Ontario Hybrid Corn Performance trials from
the Ottawa valley were particularly interesting and sparked a detailed examination
of temperatures and heat accumulation in some more detail. As illustrated in
the previous table, Ottawa got off to an early start and continued on to register
a total OCHU accumulation of 3322 for the season. Pretty impressive! The intriguing
part of the heat story is that although Ottawa had record heat accumulation,
farmers there escaped much of the intense July/August heat normally associated
with these warm seasons. Table 2 compares three of the highest heat unit accumulation
seasons in recent years and illustrates that 1998 had significantly fewer days
in July and August where temperatures reached over 30 degrees C than in two
other relatively warm seasons. In fact, the area had fewer hot days in 1998
than even the average for the past 11 years.
- Heat unit accumulation and high temperature days in Ottawa.
Days over 30
degrees C in July and August
Undoubtedly this lack of mid-season high heat stress contributed to the high
corn yields recorded in this area. It was probably a significant factor in producing
above-average corn yields in other areas of the province, especially those which
received considerably less rainfall than the Ottawa area. For example, in 1998,
Ridgetown recorded only six days in July and August where temperatures reached
over 30 degrees C, spread fairly evenly over the two months. A warm spring and
a moderate summer was generally followed in most areas by a fall which was free
of any prolonged cold snaps which tend to uncouple grain filling, lower test
weights and raise harvest moistures.
Talking about the weather is
fine. Most of us get a fair bit of practice. However, there are some points
for corn producers to consider for 1999 that stem from weather issues.
1. Odds are significantly against having another year like 1998 in 1999. Long-range
forecasts are calling for a delayed, cooler than normal spring in 1999. This
may or may not be correct, but dont let the fact that full season hybrids
for your area were harvested at 18 per cent moisture this year cause you to
select too many hybrids that are full season or beyond for your farm.
2. Bt hybrids seemed to be particularly suited (and perhaps need) a longer growing
season like 1998. Be particularly careful of planting a high percentage of full-season
Bt hybrids if the season gets off to a slow start.
3. If 1999 comes in warm and early like 1998 and soil temperatures get above
10- to 12-degrees C in late April, plant at least some of your corn and take
advantage of the potential early growth. Being overly preoccupied by the potential
of a killing June frost is pointless.
4. We certainly can't count on Mother Nature to buffer our corn crops against
heat stress the way she seemed to in 1998. The greatest buffer to corn plant
stress that producers have and that we can do anything about is the soil. Although
economic realities make it difficult we must continue to look for ways to keep
cereals in our rotations, underseed red clover or other cover crops and use
tillage systems which conserve top soil and soil moisture.