# Presentation: 656031

## Compaction and Soil Moisture

- NWISRL

**Compaction and Soil Moisture**

**Bob Sojka**

- Far West
- Agribusiness Association
- 32nd Annual
- Fertilizer & Chemical
- Conference
- Jackpot, NV
- January 10-12, 2005

**Notes:**
Single yellow flower in a field of Wheat.  1995.

## 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**

## What We’ll 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**

## Three Phase Soil Model

**NWISRL**
**Kimberly, ID**

- Sojka, 1999

## Three Phase Soil Model

**NWISRL**
**Kimberly, ID**

- Sojka, 1999

## HARDNESS

**Soil Strength**
**Mechanical Impedance**
**Penetration Resistance**
**Cone Index**

**NWISRL**
**Kimberly, ID**

## Soil Gets Harder:

- Mirreh and Ketcheson, 1972

**Soil Gets Harder:**
**When more compact**
**When dryer**

**Fundamental Soil Strength Relationships**
**Derived from In-Situ Measurements**
**Portneuf Silt Loam**

**NWISRL**
**Kimberly, ID**

- Subsoil 12-18”

- Plow Layer 6-12”

- Sojka et al. 2001

## Corn Root Growth

**Corn Root Growth**
**Through Subsoiled Portion**
**of Hardpan**
**Into Soft B Horizon**

- Norfolk loamy sand

**NWISRL**
**Kimberly, ID**

- Courtesy of Bob Campbell

**Notes:**
Corn roots, Williamson.  Row Spacing Study, Florence, S.C. 1978.  Ektachrome film.

## When roots are forced to curve, branching Is Induced.  

**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**

## BD 1.2

**BD 1.2**

**BD 1.4**

**BD 1.6**

**BD 1.8**

**PEA**

- Voorhees, 1975

**NWISRL**
**Kimberly, ID**

## COTTON

**COTTON**

- Amarillo Fine Sandy Loam

- Taylor and Gardner, 1963.

## 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**

## COTTON

**COTTON**

- Tackett & Pearson
- 1964

**Notes:**
Soil Physical Chemical Aspects

## Poorly Aerated Roots Close Stomata

- Sojka, 1988

**NWISRL**
**Kimberly, ID**

## Low Root O2 Cuts Photosynthesis

- Oosterhuise et al., 1986

**NWISRL**
**Kimberly, ID**

## Soil Oxygen in Alfalfa as Affected by Irrigation

**Soil Oxygen in Alfalfa as Affected by Irrigation**

- Meek et al., 1986

**NWISRL**
**Kimberly, ID**

**Notes:**
Meek, B.D. et al.  1986.  Alfalfa Stand Losses from Irrigation:  Influence of Soil Temperature, Texture, and Aeration Status.  Soil Sci. Soc. Am. J. 50:651-655.

## 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 isn’t restricted water can be available over a longer drying period... but roots have usually already been restricted

**NWISRL**
**Kimberly, ID**

## Compaction Squeezes Water Out of Big Pores

**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

## 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**

## Carleton, 1971

**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**

**Notes:**
Compaction of Agricultural Soils, Fig 5.36, Carleton 1971

## Compaction decreases the numbers of interconnected large pores, so infiltration rate decreases.

- Flocker et al. 1958  SSSAP 22:181-186

**Compaction decreases the numbers of interconnected large pores, so infiltration rate decreases.**

**Notes:**
Compaction of Soil with Cover Crop, Fig 1, Flocker 1958

## SOFTNESS

**Plastic Limit:**
**Wet enough for**
**Permanent Deformation**
**(Lower Plastic Limit)**

**NWISRL**
**Kimberly, ID**

## SOFTNESS

**Liquid Limit:**
**Wet enough to flow**
**(Upper Plastic Limit)**

**NWISRL**
**Kimberly, ID**

## Soils Compact More Easily as Water Content Increases

**Soils Compact More Easily as Water Content Increases**

## Sandier Soil Compacts to Higher Bulk Density than Loamy or Clay Soils

**Sandier Soil Compacts to Higher Bulk Density than Loamy or Clay Soils**

- Hovanesian and Buchele, 1959

## Compaction Footprint

**Compaction Footprint**
**Underground Is Wider**
**Than the Tire**

- Vanden Berg et al., 1957

## Depth of Compaction Increases With Load

**Depth of Compaction Increases With Load**

## Dr. Al Trouse

**NWISRL**
**Kimberly, ID**

**Notes:**
1980

## Traffic/Tillage Pans

**Traffic/Tillage Pans**
**Norfolk loamy sand**

**NWISRL**
**Kimberly, ID**

**Notes:**
1980

## Soil Compaction in Alfalfa As Affected by Amount of Traffic

- Meek et al., 1988

**Soil Compaction in Alfalfa As Affected by Amount of Traffic**

**2 ft**

**1 ft**

**6 inch**

**NWISRL**
**Kimberly, ID**

**Notes:**
Meek, B.D. et al.  1988.  Soil Compaction and its Effect on Alfalfa in Zone Production Systems.  Soil Sci. Soc. Am. J. 52:232-236.

## Determinate Southern Soybean

**Subsoiled at Planting**

**Not Subsoiled**

**NWISRL**
**Kimberly, ID**

- Mr. Bob Campbell

**Notes:**
Dargan SB, 1980

## CORN

**CORN**

- Sojka et al., 1991

- Norfolk loamy sand

## Pratt Fine Sandy Loam

**Fertilized**

**Unfertilized**

**SUGARBEET**
**Root Weights**
**kg**

**Notes:**
Soil Strength Root Growth Yield

## Mapfumo et al., 1998

**Notes:**
Mapfumo, E. et al.  1998.  Forage Growth and Yield Components as Influenced by Subsurface Compaction.  Agron. J. 90:805-812.

## Mapfumo et al., 1998

**Notes:**
Mapfumo, E. et al.  1998.  Forage Growth and Yield Components as Influenced by Subsurface Compaction.  Agron. J. 90:805-812.

## Mapfumo et al., 1998

**Notes:**
Mapfumo, E. et al.  1998.  Forage Growth and Yield Components as Influenced by Subsurface Compaction.  Agron. J. 90:805-812.

## 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**

## 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**

## 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**

**Notes:**
High Water Contents

## Slide 41

**Notes:**
Row Spacing Study, Florence, S.C.

## Sojka and Bjorneberg, Current Research

- Subsoiling Plus Polymers

## Mixing fines into sandy soils can worsen the soil strength of a compaction prone soil by achieving the “Minimum Void Ratio.”  

**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”).**

## 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

**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**