Yield Makers and Breakers
Although much of the anxiety and
nearly all of the management goes into the corn crop before July 1, the
conditions that will make or break corn yield mostly come after Canada Day.
Drought
July rainfall can have a huge impact on corn yields, especially if the lack
of rain puts the crop under drought stress during the critical period around
silking. Table 1 indicates that drought stress during this period has the
potential to trim 8 bushels per day from an expected 125 bushel/acre crop.
Heat
High temperatures in June and July speed leaf area expansion, and the crop
arrives earlier at the point of being able to intercept nearly all of the
incoming sunlight. If full crop canopy is advanced by one week, the potential
exists for yields to be boosted by 10 to 15 bushels per acre.
On the other hand, high temperatures at the time of pollination and during
the grain filling period can have detrimental effects on corn yield. High
temperatures during the grain filling period can create additional stress
on the plant, causing it to fill less efficiently. Excessive heat will shorten
the period available for the corn plant to photosynthesize while moving
starch into the kernels, thus reducing yields.
Cold
Frost at the dough stage can result in yield losses of 25-40%. Make it
to the half-milk line stage and losses will be 5-10%.
The other question regarding cold nights revolves around the corn crops'
ability to continue grain filling after experiencing cold nights where
no frost damage occurs. Dr. Thys Tollenaar, University of Guelph, has
conducted research which indicated 50% reductions in photosynthesis and
rate of grain filling due to cold nights of 2 degrees Celsius.
Conclusion
Corn producers in Ontario are not too demanding of the weatherman. Just
give us above average heat until July 15, then enough rain to thoroughly
recharge soil reserves prior to corn flowering. Finally, drop daytime
maximums to 25 degrees Celsius under clear blue skies until September
20th and we will stop complaining..at least at the weatherman.
| Table 1 Estimated yield losses caused by drought stress at various points in the development of a typical corn crop. | |
|
Date |
Estimated Yield
Loss Caused by Drought Stress |
|
May 4 - planting |
|
|
July 6 |
2.8 |
|
July 16 |
3.0 |
|
July 26 - silking |
3.5 |
|
July 31 |
6.5 |
|
August 5 |
4.0 |
|
August 10 |
4.0 |
|
Adapted from: Corn and Corn Improvement (1988) Sprague and Dudley, editors |
|