20
Innovation Plus
Crops
www.FarmProgress.com ● March 2015
Wallaces Farmer
Limit wind erosion
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OIL erosion caused by
heavy rains and water running off fields gets more
attention. But wind erosion also
occurs in Iowa, even during
winter. It’s especially noticeable
when snow in roadway ditches is
covered with black sediment from
the erosive force of wind, even at
subzero temperatures.
Of course, water erosion is a
major concern. “Erosion caused
by water far exceeds the amount
of sediment loss by wind because
of the high volume of precipitation Iowa receives during the
year,” says Mahdi Al-Kaisi, an
Iowa State University agronomy
professor and Extension soil
management specialist.
The powerful erosive effects
of water erosion on removing
sediment and associated organic
matter and nutrients from fields
and moving it into waterways,
streams and rivers is another
reason why erosion caused by
water gets more attention. The
water quality issue is making
headlines these days.
“However, wind erosion also
contributes to a significant loss
of topsoil, especially the loss of
organic matter at the soil surface,” says Al-Kaisi. “It’s certainly
worthwhile to do what you can to
try to prevent wind erosion from
occurring on your fields.”
Driving around Iowa, particularly in January and February,
you notice the volume of sediment accumulated in ditches or
near farm fences, with the snow
looking black.
“This phenomenon is observed in many parts of the state,
and it is worse where fields are
tilled or have no crop residue or
cover crop to prevent the wind
from dislodging soil particles,”
says Al-Kaisi. “The misconception
is that the soil is frozen; therefore,
wind erosion is not a concern in
detaching soil particles. However,
wind can have a significant effect
on soil erosion during winter, and
what we see in the ditches and
close to fields is only a small portion of the total soil loss during
the wind erosion process.”
Effects of topsoil loss
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During wind erosion, three distinct processes occur to displace
soil particles, he explains. These
include the initial process (saltation), when the wind’s force
detaches and removes soil particles, which subsequently return
to the soil surface and dislodge
other soil particles. This creates
the “creeping effect” — another
process in wind erosion.
During the creeping process,
sand particles move slowly along
the soil surface, striking other
soil particles, says Al-Kaisi. Then
WIND EROSION: Winter winds can blow soil from unprotected
fields. Here, you can see topsoil and organic matter ending up in
road ditches.
NO BLACK SNOW: “Planting cover crops and using no-till can
greatly reduce the amount of erosion during winter,” says ISU
Extension soil management specialist Mahdi Al-Kaisi.
these dislodged particles are
transported (suspension phase)
airborne for an extended period
of time. Those sediments and airborne particles are deposited at
different distances from the point
of origination or source.
“The heaviest particles are
deposited closer to the source,
and that is what we see as sediment-covered snow by the roadside, in ditches and near fences,”
he notes. “However, significant
amounts of eroded materials
with lighter density are transported greater distances and
may end up in water bodies and
other places across the landscape and in cities.”
Regardless of the type of soil
erosion, the loss of topsoil can
have a profound effect on soil
productivity, in addition to impacting water quality and air
quality, says Al-Kaisi. “The loss of
organic matter, sediments and attached nutrients is highly driven
by the intensity of tillage and lack
of crop residue, or lack of a cover
crop on the soil surface.”
No-till and cover crops
Generally, three management
practices — intact crop residue
cover, no-till and cover crop,
— will reduce wind erosion significantly, says Al-Kaisi. “Crop
residue and cover crops create
conditions at the near surface to
increase soil roughness to deflect
the wind profile above the soil
surface. This results in less erosive effects of wind to remove soil
particles. Also, crop residue and
cover crops slow down water
movement on the soil surface,
and provide better soil structure for increased soil porosity
and water movement into and
through the soil profile.”
The combined effects of crop
residue on the soil surface and
cover crops growing in the field
lead to less eroded sediment,
and they reduce wind erosion.
“Crop residue and cover crops
have the dual effect of stabilizing
the soil structure and reducing
the effect of wind and water erosion,” says Al-Kaisi.
Time to check your fields
Al-Kaisi encourages farmers to
give some thought to fields that
experienced wind erosion this
winter. Are there areas of fields
that would benefit by leaving
crop residue untouched in the
fall? Would the entire field or
even part of the field benefit from
planting a cover crop?
Once the snow cover is gone
this spring, it’s also a good time
to evaluate rill and gully erosion
in fields that has occurred since
last fall, he says. Spring rains tend
to cause these areas to show up
more strongly. But often you can
determine these areas before
planting and see where grass waterways and other soil conservation measures are needed.
For information on soil management and erosion control,
visit Mahdi Al-Kaisi’s website at
agronext.iastate.edu/smse.