What is Soil Compaction?
(Crystal) Ying Chen (Ph.D., P.Eng)
Department
of Biosystems Engineering
Soil compaction is
l Soil
particles being pressed together
l Reduction
of large pores within the soil
What causes soil compaction?
What is the primary cause for soil
compaction?
Wheel traffic - Static force
l Static
force is simply the weight of the machine
l Acts
vertically on soil surface
l This
compaction force can be reduced by minimizing the weight of the machine
Wheel traffic – Shear force
l Shear
force developed by the traction force (pull) of the machine
l Shear
compaction occurs at the interface between tire lugs and soil
l This
compaction force can be changed by reducing wheel slip
Shear force – no-tillage
l Pressure under tire lugs is less uniform on no-till
soil
l The lugs have considerable contact with no-till soil,
which can affect compaction
l Changing lug size may affect soil compaction on
no-till fields
Machine parameters
l Axle
loads which can altered by the number of axles or running gears
l Ground
pressure which can be altered by tires (size or duals)
How does machine parameters affect compaction?
l More
surface compaction is caused by higher ground pressure; using large tires or
duals.
l Deep
compaction is caused by high axle loads; reduce axle load.
How does compaction develop?
l The
amount of water in the soil has more effect on compaction than any other
factors
l Soil
type, soil organic matter
l Worst
case: wet clay soil with low organic matter
Why is soil compaction important?
l Balance
of air and water in soil
l Soil
erosion
l Water and
nutrient up-take
l Crop
yield
What
are the indicators for soil compaction?
l Soil bulk density
What are the indicators for soil compaction?
l Soil cone
index
l Measured
by soil cone penetrometers
l Expressed as the force (converted to pressure) required to advance a
cone into a soil mass
Research data
Soil density vs. organic matter under
no-tillage
Soil cone index – typical depth profile
Soil cone index – different layers
Soil cone index – hard pan
Soil cone index – wheel track
Quiz – previous crop
l Which of
the followings, as the previous crop, will give a softer ground: wheat or pea?
Winter freezing helped reducing compaction
in a heavy clay soil, MB
Take home messages
How to manage your soil compaction?
l Check the soil compaction status
–
Talk to universities or Extension
Specialist for a penetrometer and density sampler to measure compaction
–
Using a shovel, dig into an area
with wheel track, then dig into a wheel track to compare the resistance
How to manage your soil compaction?
l Check the
field; water ponding may indicate compaction
l Check
root growth; roots growing horizontally indicate compaction
How to manage soil compaction?
l Identify "compaction management zones" in
your fields
l Frequent observation of crops; yellow plants may be
the indication
Can I count for freezing and cracking for
compaction reduction?
l Freezing and
thawing over winter reduces compaction of top soil
l Needs several
freeze-thaw cycles
l Help top soil
l Whether it
helps for deep soil depends on how many freeze-thaw cycles
l Cracking during
summer reduces compaction
l Penetrates
compacted layers
l Creates
vertical channels in soil
l Help roots
development
l Promotes water
infiltration
How to reduce soil compaction?
l Stay out of wet soil
l Reduce
wheel traffic
l Controlled
traffic
•
Traffic is limited to prepared
pathways
How to reduce soil compaction?
l Reduce
machine weight or/and using wide tires
l Reduce
wheel slip
l Use pea
crop in the rotation
l Use
perennial crops in the rotation
How to reduce soil compaction?
Practice
no-tillage