NWISRL

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NWISRL
Compaction and Soil Moisture
Far West Agribusiness Association 32nd
Annual Fertilizer Chemical Conference Jackpot,
NV January 10-12, 2005
Bob Sojka
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Good News Bad News

• The Good News
• We know quite a bit about soil moisture
• We know quite a bit about soil compaction
• We know quite a bit about their effects in many
  crops
• The Bad News
• Alfalfa is not one of the crops we have a lot of
  specific information on for compaction

NWISRL Kimberly, ID
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What Well Cover

• Basic 3-phase Soil Physical Model
• General plant responses to compaction
• Effects of compaction on soil bulk density,
  strength, moisture, and aeration
• Effects of soil moisture on compaction
• Some data from Alfalfa
• Some management tips

NWISRL Kimberly, ID
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Three Phase Soil Model
Sojka, 1999
NWISRL Kimberly, ID
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Three Phase Soil Model
Sojka, 1999
NWISRL Kimberly, ID
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HARDNESS Soil Strength Mechanical
Impedance Penetration Resistance Cone Index
NWISRL Kimberly, ID
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Soil Gets Harder When more compact When dryer
Mirreh and Ketcheson, 1972
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Fundamental Soil Strength Relationships Derived
from In-Situ Measurements Portneuf Silt Loam
Subsoil 12-18
Plow Layer 6-12
NWISRL Kimberly, ID
Sojka et al. 2001
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Corn Root Growth Through Subsoiled Portion of
Hardpan Into Soft B Horizon
Norfolk loamy sand
Courtesy of Bob Campbell
NWISRL Kimberly, ID
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When roots are forced to curve, branching Is
Induced. Hard soil resists root penetration,
bending the root, inducing branching, further
reducing penetration
Lateral Meristem
Russell and Goss, 1974
NWISRL Kimberly, ID
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BD 1.2
BD 1.4
PEA
Voorhees, 1975
BD 1.8
BD 1.6
NWISRL Kimberly, ID
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Amarillo Fine Sandy Loam
COTTON
Taylor and Gardner, 1963.
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Three Phase Soil Model
SOIL AERATION Compacting soil decreases the
proportion and total amount of voids. The gases
are pushed out. The water remains. Water fills
a larger proportion of the remaining voids and
the water films become thicker. O2 diffuses in
through water only one ten-thousanth as easily as
through soil air
NWISRL Kimberly, ID
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COTTON
Tackett Pearson 1964
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Poorly Aerated Roots Close Stomata
Sojka, 1988
NWISRL Kimberly, ID
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Low Root O2 Cuts Photosynthesis
Oosterhuise et al., 1986
NWISRL Kimberly, ID
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Soil Oxygen in Alfalfa as Affected by Irrigation
Meek et al., 1986
NWISRL Kimberly, ID
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Three Phase Soil Model
WATER RETENTION Compacting soil decreases the
average size of voids. Less water is held at
field capacity. Water is more subject to
capillary action, so more water is available at
greater suction (lower water potentials). If
root growth isnt restricted water can be
available over a longer drying period but roots
have usually already been restricted
NWISRL Kimberly, ID
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Compaction Squeezes Water Out of Big Pores But
Holds Water Tighter in Small Pores This changes
water holding properties and soil aeration
properties
Hillel, 1971
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Three Phase Soil Model
WATER CONDUCTIVITY Compacting soil decreases
the average size of voids. Smaller pores, Less
water flow at saturation. Water is more subject
to capillary action, so more water flows in the
dryer range (up to a point).
NWISRL Kimberly, ID
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As Compaction Increases Water flow through
large pores decreases, but flow through small
pores increases. Saturated Conductivity
Decreases Unsaturated Conductivity Increases (to
a point)
High BD
Low BD
Carleton, 1971
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Compaction decreases the numbers of
interconnected large pores, so infiltration rate
decreases.
Flocker et al. 1958 SSSAP 22181-186
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SOFTNESS Plastic Limit Wet enough for Permanent
Deformation (Lower Plastic Limit)
NWISRL Kimberly, ID
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SOFTNESS Liquid Limit Wet enough to flow (Upper
Plastic Limit)
NWISRL Kimberly, ID
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Soils Compact More Easily as Water Content
Increases
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Sandier Soil Compacts to Higher Bulk Density than
Loamy or Clay Soils
Hovanesian and Buchele, 1959
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Compaction Footprint Underground Is Wider Than
the Tire
Vanden Berg et al., 1957
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Depth of Compaction Increases With Load
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Dr. Al Trouse
NWISRL Kimberly, ID
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Traffic/Tillage Pans Norfolk loamy sand
NWISRL Kimberly, ID
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Soil Compaction in Alfalfa As Affected by Amount
of Traffic
Meek et al., 1988
6 inch
1 ft
2 ft
NWISRL Kimberly, ID
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Determinate Southern Soybean
Subsoiled at Planting
Not Subsoiled
Mr. Bob Campbell
NWISRL Kimberly, ID
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Norfolk loamy sand
CORN
Sojka et al., 1991
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Pratt Fine Sandy Loam
Fertilized
SUGARBEET Root Weights kg
Unfertilized
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Mapfumo et al., 1998
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Mapfumo et al., 1998
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Mapfumo et al., 1998
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Anti-Compaction Tips AVOID FIELD OPERATIONS ON
WET SOIL Conserve Soil Organic Matter Control
Wheel Traffic Patterns Minimize Operations and
Traffic Keep Axle Loads to a Minimum Match-up
Tractors, Implements, Tires, Trailers
etc. Preserve Organic Matter and Soil
Structure Break up Compacted Soil if Needed AVOID
FIELD OPERATIONS ON WET SOIL
NWISRL Kimberly, ID
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Structured vs Massive Soil

• Soil without structure is more easily compacted
• Structure provides voids for gas and water
  exchange and potential root channels
• Soil Structure tends to be enhanced and
  stabilized by Soil Organic Matter and a mixture
  of particle sizes

NWISRL Kimberly, ID
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• Wet Soil
• Weakens structure (easy to compact)
• Lowers O2 availability to plant roots
• Favors microbial activity if warm
• Can promote disease if prolonged
• Can leach nutrients / agrichemicals
• Can cause reducing conditions (Gaseous N-loss)

NWISRL Kimberly, ID
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(No Transcript)
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Sojka and Bjorneberg, Current Research
Subsoiling Plus Polymers
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Mixing fines into sandy soils can worsen the soil
strength of a compaction prone soil by achieving
the Minimum Void Ratio. It takes 100s of
tons of silt and clay per acre to convert a sandy
soil to a loam (surface 6).
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Only a few tons of manure per acre can change the
tilth of the of a sandy soil, by promoting
inter-aggregate structure, allowing the soil to
perform more like a loam