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Let the soil be your guide
For healthier cotton, go by the ground, not the calendar
c
otton can overcome many
stresses if it has adequate soil
and air temperatures for plant
growth. However, growers in
most regions of Texas plant before the onset
of optimum temperature conditions to take
advantage of early season moisture. Growers in the eastern part of the state prefer
earlier plantings to avoid late season harvest
problems, and growers in the western
regions plant early in an attempt to lengthen
their growing season. However, it is best to
plant according to soil temperature — not
the calendar. If planted too early, a crop
may suffer stand loss and cold temperature
stress, which reduce yield potential.
The seed is known as a “resting” structure.
It is dehydrated, largely composed of storage
tissue, and surrounded by the impervious
seed coat. Basically, the seed is in a state
of suspended animation, mainly due to a
lack of water and oxygen. The process of
germination begins with the absorption of
water (imbibition), the reactivation of metabolism, and the initiation of growth. The
seed contains an embryo. At one end of the
embryo is the radicle, which will become
the root and at the other end is the plumule,
which will form the stem and leaves. The
cotton seed also has two cotyledons, or seed
leaves. These cotyledons are storage tissues
and provide energy for the developing
seedling.
Cotton seed germination is favored by
high soil oxygen concentration, adequate
soil moisture, and soil temperatures above
64 degrees F. Based on work conducted by
USDA-ARS researchers at Lubbock, the
cotton plant requires more than 100 hours
above 64 degrees F at the seed level to
emerge. Germination can begin when the
mean daily temperature is 60 degrees F at
seeding depths, but growth will be slow at
these temperatures.
The optimum planting target is to have a
10-day average soil temperature of 65 de20
At a minimum, soil temperatures in the seed
and root zone should exceed 60° F and
the five day forecast for daytime maximum
temperatures should exceed 80° F.
grees F at the 8-inch depth. If poor quality
seed is planted, then 70 degrees F may be a
better target. This volume of soil underneath
the seed can act as a potential short-term
heat buffer to moderate seed zone temperatures if cool spells do occur after planting.
This is due to the fact that soil temperatures
in the seed zone will lag air temperatures by
about 3 to 5 hours.
At a minimum, soil temperatures in
the seed and root zone should exceed 60
degrees F and the five day forecast for
daytime maximum temperatures should
exceed 80 degrees F. Additionally, nighttime minimum temperatures should be
forecast to be above 50 degrees F for the
following five days.
Cotton is a tropical plant and during the
critical germination period soil temperatures below 50 degrees F can cause chilling injury to germinating cotton. Chilling
injury can result in malformed seedlings,
loss of the taproot reduced vigor and stand
establishment, and the increased likelihood
of seedling disease problems. Emergence
will generally occur after accumulation of
50-80 DD60 heat units after planting. Planting should be delayed if the five day forecast
predicts the accumulation of less than 25
heat units after planting.