Corn Planting Time In A “Normal” Spring
URBANA, ILL.
Yes, a year does make a
lot of difference – in
2012, we had 5 percent
of the Illinois corn crop
planted by April 1 and 17 percent
planted by April 9. This
year, the April 8 issue of Illinois
Weather & Crops from
the Illinois office of NASS
gives no percentage planted as of April 7, which
means that less than 1 percent had been
planted. There has been some planting this
week, but with soils still cool and rain in the
forecast, along with a drop in temperatures into
the 30s at night later this week, many producers
are proceeding with caution.
According to the Illinois State Climatologist’s
office, soil temperature at the 4-inch depth at
10 AM averaged in the mid-30s on March 20,
2013, compared to the upper 50s on the same
date in 2012. Soils have warmed since then, but
according to the DTN/Illinois Farm Bureau
website, ranged from only the mid-50s in southern
Illinois to the upper 30s in the northern
edge of the State on April 9, 2013. With cool
weather returning late this week, soil temperatures
are likely to decrease. And wet soils warm
more slowly than dry soils, so we may be in for
some “patience-requiring” weather.
Cool soils by themselves don’t represent much
threat to corn seed, but soils that are both cool
and wet slow germination and emergence, and
provide an advantage to microbes in the soil
that can attack corn seed. Some producers may
be inclined to set planting depth a little shallower
in an attempt to help with emergence
under such conditions. That can help sometimes,
but the shallowest-placed seed after
planting should never be less than about 1.25
inches deep, and planter settings should seldom
be less than 1.5 inches deep. Remember, too,
that soil close to the surface both warms faster
during the day and cools down faster at night
than soil beneath the surface, so the overall effect
of shallower placement on temperature experienced
by the seed and seedling might not be
very predictable.
Compared to the corn that was planted in
mid-March last year and suffered frost damage
the second week of April, the crop this year
should be in little danger of frost damage.
Chances of frost drop quickly as April progresses,
to very low levels by the end of the
month in all but the northern edge of Illinois.
That doesn’t mean zero chance – we had frost
through much of central and northern Illinois
the first week of May in 2005 – but frost through
mid- or even late April is not likely to damage
corn this year because there won’t be much
corn emerged and growing if frost occurs.
The corn planted on April 5 in our planting
date study here at Urbana has germinated and
sent out its radicle (root), but not yet the
plumule (shoot). It has accumulated some 70
growing degree days (GDDs) through April 10,
but the 10-day forecast through April 19 is for
accumulation of fewer than 50 GDDs over the
next 10 days, so I expect emergence to take another
week or so. Over the past 10 years the
GDD accumulation for April at the Champaign
airport has ranged from 210 to 344, with an average
of 263. We’re on track to accumulate normal
GDDs in April 2013. But temperatures
during April don’t always increase steadily, and
we can’t count on later planting to provide
warmer temperatures after planting. In 2012,
GDD accumulations for the first, second, and
third 10-day periods in April were 109, 94, and
80, respectively.
The variability in daily accumulation of GGDs
during April produces a wide range in number
of days – from a week to three weeks – required
for emergence. It’s not necessarily a problem for
corn to take 20 days or more to emerge, as long
as both emergence percentage and emergence
uniformity – the time between first and last
emergence within a field – are good.
Under cool temperatures, it is normal for the
emergence process to take longer, with perhaps
as much as four or five days from beginning to
end. People often worry about this, having
heard that non-uniformity of emergence costs
yield. Plants that end up being behind their
neighbors in development tend to stay behind,
and often lose out in the competition for light,
water, and nutrients. It is not the case that such
plants end up as “weeds” – that is, that they reduce
the yields of remaining plants. But the remaining
(larger) plants don’t completely make
up for the yield lost from the plants that get left
behind.
It is important that we consider the cause of
non-uniformity of emergence, however. Nonuniformity
of emergence is a problem if differences
in emergence are related to factors such
as seedling damage, soil crusting, low seed
vigor, etc. But uniformity of emergence is also
affected by temperature (GDD accumulation
rates) just as is the time between planting and
emergence. So I suggest that we consider emergence
as “uniform” from the plant development
standpoint if it occurs over the time it takes to
accumulate 20 or 25 GDD, whether that takes
one day or five days. As with other aspects of
corn development, basing events on “thermal
time” (GDDs) works better than using time
measured in hours or days. The practical effect
is that, once it warms up, plants that emerged
in 110 GDD and those that took 130 GDD to
emerge will differ very little in their stage of development.
While it takes patience to wait until wet soils
dry out before we can plant, remember that it’s
still early, and we haven’t begun to lose yield potential
from planting delays. It helps that soils
were in reasonable shape (meaning they had
warmed enough to dry out) in many parts of Illinois
by at the end of the first week of April – this
often means better chances of having them dry
out after rain, though cool temperatures will
slow that some.
While planting date responses do vary among
years and sites in our research, we can for all
practical purposes consider the planting date
response to be flat for the month of April, with
losses starting to pick up, slowly at first, starting
in early May. It pays to remember during
this time that it is easy to do more damage by
working or planting into soils that are too wet
than we could gain by planting a little earlier.
While we hope to get most of our crop planted
by the end of April, what happens after planting
remains a lot more important to the corn crop
than the exact date we are able to plant. We
need look back only one year to see that early
planting does not guarantee high yields. Δ
DR. EMERSON NAFZIGER: Professor Research
Education Center Coordinator, University of Illinois