Will The Corn And Soybean Crop Get Finished?
URBANA, ILL.
Late planting and weather
that continues to be
cooler than normal into
August has many wondering
if the corn and soybean crops
will reach maturity and harvest
moisture within a reasonable
time this fall. Crop
conditions remain good for
both crops, but crop development, including
pod formation and filling in soybean and grain
fill in corn, remains well behind normal. Corn is
10 days to 2 weeks behind normal, and soybeans
are 2 to 3 weeks behind normal. The
number of days behind will “stretch” as the
weather cools, so late crops get even later. Ten
days behind in mid-August will be become 15
or 20 days behind in mid-September, even if
temperatures are normal.
We have often pointed out that late-planted
corn tends to require fewer growing degree days
to reach maturity than does early-planted corn.
That’s often reflected in lower yields, as the crop
experiences stress during the high temperatures
and dry weather we often experience in
mid-summer. This year, however, with temperatures
generally below normal in recent weeks,
we do not expect to see this accelerated development.
Instead, we are seeing that corn development
is following closely the normal number
of GDDs required to reach each stage. This
means less chance of premature death and so a
better chance to fill grain completely. But for
late-planted corn it also means late maturity.
How late can we expect the corn crop to mature?
If we assume normal GDD accumulations
in August and September, corn planted in the
Champaign area on May 1, May 15, and May 31
will accumulate about 3,020, 2,850, and 2,530
GDD, respectively, by the end of September. If
we further assume that a mid-season (111-day
RM) hybrid needs 2,700 GDD from planting to
maturity regardless of planting date, we can expect
corn planted on these dates to reach maturity
(black layer, about 32 percent grain
moisture) about September 5-10, September
15-20, and mid-October, respectively. The crop
seems to be on course to do this: corn planted
in early May is at stage R3 (milk stage) now
while corn planted in late May or early June is
just finishing pollination. This reflects ongoing
cool temperatures so far in August, and if these
continue, maturity dates will be even later.
With a 50 percent frost date of about October
20 here, we would expect a mid-season corn hybrid
planted in early June to mature before
frost, if frost does not occur before its normal
(50 percent) date. But drydown slows quickly as
we move into October, and even early-planted
corn will dry slowly after maturity unless September
is unusually warm. Corn planted in
mid-June (some fields in central Illinois are still
not pollinated) is unlikely to mature before frost
if temperatures are normal and frost comes at
its normal time.
While the soybean crop has a dark green,
healthy appearance in most fields now, podsetting
is later than normal, and the crop planted
the second half of May has not yet reached, or
moved past, beginning podfill (stage R5). If temperatures
continue to be cooler than normal, we
can expect the crop to reach maturity only by
late September or early October. We hope not to
see a repeat of 2009, when more than half the
Illinois soybean crop was harvested after November
1. That followed a very wet October.
Beyond their effect on maturity, cool temperatures
are continuing to have a somewhat negative
effect on soybean crop. The crop has good
photosynthetic capacity due to its healthy, complete
canopy. And soil water use rates are less
than normal, extending the water supply. But
below-normal daytime temperatures (and
clouds) mean less photosynthesis, and cool
nights can physiologically limit growth rates
and the photosynthetic rates the next day. The
first effect we might see is below-normal pod
numbers, or pods initiated in late August that
might not fill.
Good soybean yields are still possible if the
weather remains good into September, but seed
filling rates will remain slow as long as temperatures
remain low. We have sometimes seen
cool temperatures trigger maturity before seeds
are fully filled. The best scenario for soybeans
would be a return to temperatures – both day
and night – return to normal or a little above
normal, with enough rainfall to enable the crop
to photosynthesize fully as seeds fill. Even with
that, we’re in for a wait to see how the crop finishes
this fall. Δ
DR. EMERSON NAFZIGER: Professor/Research
Education Center Coordinator, University of Illinois