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Planting Corn
Ron Meyer, Area
Extension Agent - Golden Plains Area
Date: 4/13/2011
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Since soil temperature,
stand establishment and uniform emergence are all key considerations when
attempting to determine an optimum corn planting window, early plantings are
generally discouraged when significant acreages are involved. Agronomy
professionals agree that the optimum corn planting window will be related
directly to a consistent soil temperature of around 50 to 55° F at the
two-inch soil depth. Traditionally, these consistent soil temperatures occur
between the third week of April through the first week of May. Since cool soils
through mid-April often result in a lengthy germination period, corn emergence
can often times take over three weeks from the time of planting to full stand
establishment. Table 1 outlines the approximate days to seedling emergence
based on various, consistent, soil temperature ranges:
Crop Observations/Management
Suggestions
Under cold weather conditions or fluctuating soil
temperatures, the coleoptile (shoot) still emerges from the seed, but rather
than growing upward towards the soil surface, it twists or curls around the
seed. The unusual growth pattern of the coleoptile is in response to cold soil
conditions; this type of growth alone is usually not cause for alarm. Once soil
temperatures improve, the coleoptile will “right” itself and grow
towards the surface, where it splits open when exposed to sunlight, allowing
the first leaves to emerge.
Corn may leaf out underground for a number
of reasons. A cloddy seedbed or improper closure of the seed furrow may allow
light to penetrate below the soil surface. If light reaches the emerging
coleoptile (spike) underneath the surface, it may rupture, causing the leaves
to unfurl. Cold soils and compacted and/or crusted soils can also lead to
leafing out underground. Some herbicides occasionally magnify the corkscrew
problem with the soil conditions mentioned above.
Once corn is emerged
other issues can express themselves. Purple Corn Syndrome shows up in a handful
of cornfields nearly every year. This purple seedling color results from the
expression of genes for anthocyanin pigment formation. Most corn hybrids
contain 5 of the necessary 8 genes required to produce this purple color, while
the other 3 genes are present in only certain hybrids suggesting this attribute
is a “genetically inherited” trait more prominent in certain hybrids
over others.
Since several of these genes are cold sensitive, overnight
temperatures in the 40s with daytime highs in the 60s are often sufficient to
trigger a purpling effect on corn leaves. Since these temperature sensitive
genes are only expressed in seedlings prior to the six-leaf stage of growth,
this early developmental stage often coincides with the same period most likely
to have lower temperatures. Corn usually outgrows the condition by the time it
is 12 inches tall. This occurs quickly if weather remains conducive for rapid
growth or slows if conditions remain cool enough to retard root and shoot
growth.
Realizing that cool temperatures, not the purple pigment itself,
results in slow plant growth is important. Extensive research has been
conducted on purple corn with no negative yield implications
observed.
Source: Pioneer Hi-Bred Intl