Minnesota Crop News > 2001-2008 Archives
Compaction: What Can You Do?
Regional Extension Educator
As you start heading back into the fields this spring,
try to think about reducing your soil compaction. As the
weight of farm tractors and field equipment becomes larger
and heavier and as the annual precipitation increases in
Minnesota, there is a growing concern about soil compaction.
Soil compaction can be associated with a majority of field
operations that are often performed when soils are wet
and more susceptible to compaction. Heavy equipment and
tillage implements can cause damage to the soil structure.
Soil structure is important because it is the number one
defense the soil has against compaction and it determines
the ability of a soil to hold and conduct water, nutrients,
and air necessary for plant root activity.
Myths about Soil Compaction
There are two wide spread myths about compaction; 1.)
Freeze-thaw cycles will alleviate a majority of soil compaction
created by machinery, and 2.) What compaction “Mother
Nature” does not take care of, deep tillage or subsoiling
Although soils in this region are subject
to annual freeze-thaw cycles and freeze to depths of 3
feet or more, only the top 2 to 5 inches will experience
more than one freeze-thaw cycle per year. The belief that
freeze-thaw cycles will loosen compacted soils may have
developed years ago when compaction would have been relatively
shallow because machinery weighed less and grass and legumes
were grown in the rotation.
Both heavy axle loads and wet soil conditions increases
the depth of compaction in the soil profile. Compaction
caused by heavy axle loads (greater than 10 tons per axle)
on wet soils can extend to depths of two feet or more.
Since this is well below the depth of normal tillage, the
compaction is more likely to persist compared to shallow
compaction that can be largely removed by tillage.
While deep tillage (greater than 18 inches) is capable
of shattering hard pans created by wheel traffic, it has
not been proven to increase yield consistently or for long
periods of time. In the Midwest , research results have
shown few positive yield responses to subsoiling, and when
they occur, are variable and relatively small. It is difficult
to accurately predict the effects from subsoiling because
of differences in soils, degree of subsoil compaction,
soil moisture, future traffic, weather conditions, and
differences in the crop grown and in tillage methods.
Tire Inflation Pressure (psi)
versus Axle Load
Tractors equipped with either tracks or tires can create
surface compaction. The question is “Which one creates
the least amount of compaction”? The answer: both
radial tires, properly inflated, and tracks will result
in similar surface compaction.
Tractors weighing less than 10
tons an axle usually keep compaction in the top 6-8 inches,
which can be alleviated by tillage. By and large, even
the biggest tractors weigh less than 10 tons an axle. However,
full combines, slurry tankers, and grain carts weigh much
more (between 20 and 40 tons an axle) and whether equipped
with tracks or tires, can create compaction as deep as
Compaction in the surface layer (6-8 inches) is largely
related to the inflation pressure (psi) of
the tire while depth of compaction is related to total
axle load. This is important when comparing tracks
and tires for compaction effects and depth.
Tracks exert a ground pressure of approximately 4-7 psi
depending on track width, length, and tractor weight. Radial
tires exert a pressure of 1-2 pounds higher than their
inflation pressure. For example, if a radial tire is inflated
to 6 psi, the tire exerts a pressure of 7-8 psi on the
soil. Since tracks and tires carry similar loads and have
low soil pressure, they both exert similar stress onto
One of the most important factors for decreasing the
potential for soil compaction is staying off the soil when
it is wet. Since farmers have a small window of opportunity
for planting their crops, this is not always possible.
Other effective strategies are to maintain proper tire
inflation rates and decrease axle loads. Radial tires can
be inflated as low as 6-8 psi. Check with your dealer to
establish the proper tire pressure for your tractor. Before
using any equipment in the field make sure to check your
tire pressure. Not only does this help reduce soil compaction,
it also improves tractor efficiency.
Your soil is one of the most important factors when growing
a healthy crop. Preventing soil compaction will increase
water infiltration and storage capacity, timeliness of
field operations, decrease the stress on plant roots, and
decrease disease potential. By simply inflating your tires
to their proper air pressure, you can reduce surface soil
compaction and by reducing axle loads, it will reduce the
depth of compaction in the soil.
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