Wallace's Farmer, IA
05-07-07
Corn Planting - Did You Get It Done Before Rain?
Rod Swoboda rswoboda@farmprogress.com
Optimum corn planting dates for Iowa are considered to be from April 20 to May
15. Early planting is influential in shifting the date of corn pollination earlier in the
growing season. The objective with earlier pollination is for improved light quality,
longer day length and usually cooler air temperatures.
For those farmers who got corn planted before the recent rain, the rain cooled
the soil down a little so you can expect emergence to take a little longer, says
Mark Licht, Iowa State University Extension crop specialist at Carroll in
western Iowa. If you had or have standing water, remember that germinated
corn can survive two to three days under water. Cool, wet soils now may trigger
seedling diseases later this spring.
For more information regarding corn survivability in flooded areas, visit
www.agronext.iastate.edu/corn.
"For farmers who did not get corn planted before the rain, a lot of corn can and
will be planted in the next two weeks. There is no need at this point to make a
switch to a shorter-day hybrid," says Licht. "Corn has some ability to alter its
development. Remember to take care to make sure the seedbed environment is
favorable for planting, especially pay attention to topsoil moisture."
Corn survival in saturated fields
Rainfall that fell from April 22 to 26 resulted in totals of 2 to 8 inches of rain
across Iowa. Soils became saturated resulting in widespread flooding and
ponding. A range existed across the state with some farmers in a few areas
nearly completed with corn planting while many in Iowa had not started.
Although some acres have been planted, there were only a few fields of corn
reported to have emerged as of April 30. In fields that were not flooded, the
persistent hammering of rain will most likely result in thick soil crusts, which could
inhibit emergence.
Many fields were flooded or had ponds. Most fields had saturated soils. How long
can corn survive? "Smaller seedlings are more susceptible than larger
seedlings," says Roger Elmore, ISU Extension agronomist. "We admit that the
effect of standing water on germinating seeds is not well known. Some hybrids
will probably respond better than others, yet differentiating among poor and good
hybrids is not possible due limited data."
Four days is about the limit
A germinating seed is a living organism and requires oxygen to survive, explains
Lori Abendroth, ISU extension corn specialist who works with Elmore. "In
flooded soil conditions, the oxygen supply will become depleted within
approximately 48 hours. Cool air temperatures help to increase the possibility of
survival. Yet, we wouldn't expect survival of germinating seeds to be greater than
that of young plants. They should not be expected to survive more than four
days."
After the waters go down, plant survival should be confirmed by examining the
color of the growing point of the seedlings, if present. The radicle (root) and
coleoptile (shoot) should appear white or cream colored. Seeds could be cut in
half to determine if turgor pressure is still present. If the seed is extremely soft
and does not hold form, it probably will not survive, says Abendroth. Surviving
plants will resume growth within three to five days after the water recedes.
Making the decision to replant
A decision to replant should be made only after assessing stands and
considering the economics of replanting or converting the acreage to soybean or
another crop. An ISU Extension publication to help you determine when to
replant is the Corn Planting Guide (PM 1885). Corn planted prior to May 15
would be expected to yield similarly to the corn that was already planted if stands
are comparable and diseases do not infect the seed or seedling.
"Therefore, if stands are extremely poor, replanting would be a good option," she
notes. "Although, be aware that conditions can change quickly with several good
days of weather."