Page 8-Corn Talk. Lancaster Farming, Saturday. October 14, 1995
POPULATION EFFECTS
OF DIFFERENT
CORN HYBRIDS
Greg Roth
Penn State Agronomy
Associate Professor
One of the major factors that
has resulted in higher yields in
com has been the development
of tolerance by modem hybrids
to higher plant populations.
Since 1560, plant population
recommendations have
increased from an average of
15,000 plants per acre to 25,000
plants per acre or more. Conse
quently, we need to continue to
be reevaluating the yield
response to plant population.
A recent study was con
cluded at Ohio State by P. R.
Thomison and D. M. Jordan on
the effects of plant population
on four com hybrids that pro
vides some insight
into how modern
hybrids respond to
plant population. The
results were pub
lished recently in the
Journal of Production
Agriculture.
These researchers
conducted a total ol
11 experiments at
seven locations in
1990 and 1991. In
each experiment, four
hybrids were eva
luated at 16,000,
24,000, and 32,000
plants per acre. The
four hybrids were
characterized as a
single ear flex hybrid,
a single eared fixed
hybrid, a semiprolific
hybrid, and a prolific
hybrid. Prolific
hybrids tend to pro
duce more than one
ear per stalk.
The terms “fixed’’
and “flex” refer to the
response of ear size to
population. A fixed
ear does not increase
in size with a reduced
population whereas a
flex ear hybrid
increases in size as the
population decreases.
Grain yields in this
study were generally
good with 1990 sites
yielding slightly more
than those in 1991. In
1990, yields ranged
from 148 to 180
bushels/acre while in
1991 yields ranged
from 124 to 174
bushels/acre.
In 1990, grain yield
was highest at the
32,000 population at
five of the six sites. In
1991, yields were highest for
the 32,000 population at only
one site and highest for the
24,000 population at three sites.
In general, the yield response
to the high populations was not
as great under stress but yields
did not decline appreciably at
the high population.
Hybrid differences in proli
facy and ear growth habit had a
relatively small effect on the
response to increasing popula
tion. In 1990, the single-eared
and semi-prolific hybrids
required a higher population
(32,000) than the prolific
hybrid to achieve maximum
yields, but this did not occur in
1991 when all hybrids achieved
the highest yields at 24,000.
Consequently, the researchers
were unable to show a differ
ence in the yield response to
population between the fixed
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and flex ear hybrids as might be
expected.
Lodging was increased at the
higher population and with the
prolific and semiprolific
hybrids. Increasing the popula
tion from 24,000 to 32,000
increased the lodging of the fix
ed and flex hybrids only about 1
to 2 percentage units averaged
over all 11 sites. When popula
tions were increased from
24,000 to 32,0)0, lodging was
increased by more than 5 per
cent in only two of the eleven
sites.
This study supports some of
the plant population responses
we have observed in Pennsyl
vania, such as: 1) higher popu
lations (greater than 24000)
will sometimes result in higher
yields but often will not reduce
yields, 2) yield responses to
higher populations are most
likely under low stress condi
tions, and 3) modem single
eared hybrids stand well even at
high populations.
This study suggests there
may be potential for increasing
yields with populations higher
than 24,000 on soils with reaso
nably good yield potential. On
some of our droughty Pennsyl
vania soils with 100 bushel or
less yield potential, increasing
populations above 24,000 may
not be appropriate.
Crops Conference
CARLISLE (Cumberland
Co.) The Pennsylvania
Crops Conference has been
scheduled for Tuesday, Jan. 30,
1996 here at the Embers Inn
and Cgnvention Center.
This year’s conference will
include presentations from
NCCJA executive vice presi
dent Keith Heard from
NCGA’s Washington office
describing the upcoming Farm
Bill Legislation and the status
of Full Farm Flexibility, a legi
slative initiative of NCGA.
Growers will also hear from
growers and industry personnel
who have had some of their first
experiences with yield moni
tors this fall in the field.
Also on tap are presentations
the use of options in grain
marketing and the results of the
Pennsylvania Five Acre Com
Club.
This year’s conference will
be cosponsored by the Pennsyl
vania Forage and Grassland
Council (PFGC) and the Pen
nsylvania Soybean Promotion
Board.
PFGC breakout sessions will
focus on making the transition
to grazing ,md ways to reduce
the labor associated with forage
harvesting. The Pennsylvania
Soybean Promotion Board has
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invited John Bechercr, the CEO
of the United Soybean Check
off Board, who will discuss
how the soybean checkoff
funds are being used at the
national level to develop new
markets for soybeans.
If you are a serious grain or
forage producer in Pennsylva
nia, you should marie you calen
dar and plan to attend this
conference.
Registration information
will be available soon at local
extension offices or can be
obtained from the Penn State
Agronomy Department at (814)
865-2543.
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