Got Water? Crop Thirst
Depends On Soil Type
COLUMBUS, Ohio The
biggest element in the world of
agricultural production that
makes or breaks a crop is
water.
“The biggest risk to produc
tion is not practices like fertil
ization, but the amount of
water present in the soil,” said
Brian Slater, an Ohio State
University natural resources
researcher. “The limitation of
water impacts a crop’s growth
potential and does have an in-
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fluence on other production
practices.”
Slater and his colleagues
are using geospatial technolo
gy to map soil water levels in
fields and demonstrate how
growers can use information
on water-deficit areas or satu
rated fields to better manage
their crop. Geospatial technol
ogies include remote sensing,
geographic information sys
tems (GIS), global positioning
systems (GPS), data recording
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“Knowing a crop requires
different management prac
tices even in different parts of
the same field as a result of
varying water levels can help
produce those maximum
yields,” said Slater.
The first step to realizing a
soil’s water capacity is to un
derstand the type of soil one is
dealing with. More than 480
different soil series have been
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identified in Ohio, each with a
different set of characteristics
reflecting how the soil formed.
The amount of water that a
soil can hold is dependent
upon a variety of factors in
cluding: how much rainfall
the soil receives during the
growing season; the water
needs of the crop (com is
more water-dependent than
other crops like wheat); what
type of production a farmer
practices (no-till or conserva
tion tillage provides better soil
filtration); and if the soil is sit
uated to receive run-off.
Ultimately, however, it’s the
size of the particles that make
up the soil that determines
whether the soil holds onto
water or quickly loses it. Clay
soils, for example, are made
up of fine particles that hold
onto water very easily, but
make it difficult for plants to
access.
“In clay soils, the soil parti
cles have an enormous surface
area. The soil absorbs large
amounts of water but holds on
to it very tightly, resulting in a
less available water capacity
for plants,” said Slater. “As a
result, it takes large amounts
of water for the soil to reach a
water content that is available
for plants.”
This explains why fields
throughout north and north
west Ohio, comprised predom
inately of clay soils, have been
suffering from insufficient
rainfall this growing season.
At the other end of the
spectrum are sandy soils.
Made up of very large parti
cles, they don’t hold on to
water well and, as a result,
drain much quicker.
Slater said the ideal soil is
silt loam, a mixture of fine
and large particles that offers
a range of water holding ca
pacity. “Ohio is fortunate in
that silt loam is a common soil
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texture in the state, and many
Ohio soils have a high water
holding capacity,” said Slater.
Once a grower knows what
type of soil(s) his field has, he
can then determine the water
holding capacity and use that
number as a guide for calcu
lating the water needs of his
crop. County soil surveys are
available from the U.S. De
partment of Agriculture Soil
Conservation Service.
Ohio State researchers have
also developed a comprehen
sive soil property database
that growers can access by
logging on to http://
www.ag.ohio-state.edu/
agwatmgt/tables.htm. The da
tabase provides detailed soil
information, including the
available water capacity of
every soil series identified in
Ohio.
“The database gives grow
ers some indication of what
water is available to the plant
during a normal growing sea
son,” said Slater.
Average water use of a com
crop during pollination and
grain fill is about Vi inch per
day. So, for example, with a
water storage capacity of 1.8
inches per foot, a fully
charged silty clay loam soil
might carry com with a three
foot rooting depth up to 18
days during silking and early
grain fill stages.
Said Ohio State agronomist
Peter Thomison, although
com roots can grow as deep as
eight feet, when actively grow
ing, com obtains 90 percent of
its water requirements from
the top three feet of the soil
profile.
Growers should keep in
mind that soil types have
varying water capacity depths
and different Layefti>;is soil
types that affect root growth,
especially during a period of
dry weather.
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