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Early Planted Corn Stands: Is Pretty the Best?
D.R.
Hicks, Agronomy
and Plant Genetics, University of Minnesota
March 22, 2004
We've had a significant portion of Minnesota
corn acreage planted prior to May 1 for the past two years (2002
and 2003). In both years, plant stands have not been ideal - spacing
between plants has not been uniform and final stands have been
lower than expected. Yet both years have been excellent corn production
years for Minnesota growers. The state average yield was a record
157 bushels per acre in 2002 and an impressive 146 bushels per
acre in 2003.
Early planted corn seed will lay in the ground
longer before emergence because of soil temperature. About 100
heat units
are necessary
to cause seed to germinate and emerge. Soil temperature where
the seed lays in the soil needs to be 50 degrees or higher to promote
germination and seedling growth. In late April and early May,
the
long-term average daily soil temperature at the two-inch depth
(about where the seed is) is below 50 degrees (Figure 1). The
soil temperature fluctuates around this average temperature with
part
of the day when the temperature is above average and part of
the day when the temperature is below average.
As the warming trend continues, there is a greater
portion of the day when the seed zone soil temperature is above
50 degrees. That's why early-planted corn requires more time to
emerge than does later-planted corn. The number of days from planting
to emergence is given in Figure 2 for planting dates beginning
April 15. With average soil temperatures, corn seed put in the
ground mid-April will lay there for about 25 days before emergence.
This is usually not a problem because the temperature where the
seed is laying is too low for rotting organisms to flourish, so
seeds germinate and emerge after some time.
When corn is planted later, there are fewer days that the seed
lays in the ground because soil temperatures in the seed zone are
higher. Plants will emerge in 5 to 7 days when planted in mid to
late May.
Because soil temperature is so marginal in late April with respect
to the temperature necessary to promote germination and emergence,
small differences in soil temperature can cause uneven emerging
plants with slow growth rates in mid to late May. Soil temperature
differences in the seed zone occur because of differing water conditions
and residue pieces on the surface, both of which cause the soil
to warm more slowly. Uneven emerging fields may not be as pretty
to look at as are fields planted later that emerge more uniformly
and appear to be growing faster.
Uniform stands (both spacing between plants and time of emergence)
are important to give all plants equal competition to water and
nutrients. However, non-uniform stands are productive and profitable
stands because late emerging plants do contribute to yield. Yields
from corn stands with late emerging plants are given in the Corn
Planting Newsletter (4/15/03) at http://www.corn.umn.edu.
There will be years again like the past two where stands will
not be as good as growers intend. But these early-planted stands
(lower than desired populations or uneven emerging plants or both)
have a higher yield potential than do the later-planted stands
that emerge more uniformly and appear to grow faster. Early planting
sets the stage for high yields and the greatest profitability (see
the Corn Planting Newsletter cited above for the relationship between
planting date and corn yield in Minnesota).
There are two planting
windows in Minnesota. The first is between April 15 and May 5.
Then there
is a higher probability of rainfall
that stops field work. The second window for planting begins about
May 15. Times and durations of these planting windows vary every
year, but the pattern is the same. For maximum profitability, don't
miss the first planting window!
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