SOIL COMPACTION

What is Soil Compaction

• What is soil compaction?• Compaction occurs when a force compresses

the soil and pushes air and water out of it so that it becomes more dense. Compaction is more severe when the soil is wet and less able to withstand compression.

• Soils tend to be most easily compacted when the soil water content is near field capacity.

• As the growing season nears its end there is the potential for heavy vehicular traffic from operations such as silage, forage, and grain harvest, and tillage and manure application

• Soils tend to be most easily compacted when the soil water content is near field capacity.

• As the growing season nears its end there is the potential for heavy vehicular traffic from operations such as silage, forage, and grain harvest, and tillage and manure application

• Why should I worry about it?• Compaction is a concern because it affects plant

growth. There are not enough pores or spaces in compacted soil to allow unrestricted root movement, infiltration, drainage or air circulation. The restricted roots are often unable to take up sufficient water or nutrients from the soil. The result is less plant growth and lower yields, particularly during periods of drought.

• Large spaces in soils are known as macro pores and are created by plant roots, burrowing creatures and shrinkage caused by the drying of wet soil.

• Macro pores are usually continuous and form “highways” for air and water to travel deep into the soil.

• These pores determine the soil’s physical and soil biological quality.

• Macro pores are the most vulnerable pores to soil compaction because when the tractors or animals are on top of the soil its going to fill in the bigger spaces first.

• The loss of macro porosity and pore continuity reduces strongly the ability of the soil to conduct water and air.

• This leads to run-off and eventually flooding.

Where does soil compaction occur?

• Soil compaction occurs anywhere and everywhere. • It will occur in your front yard, in your landscaping,

in your tobacco crop, and many other places.

When does soil compaction occur?

Soil compaction occurs when soil particles are pressed together, reducing pore space between them. Heavily compacted soils contain few large

pores and have a reduced rate of both water infiltration and drainage from the compacted layer.

Raindrop impact - This is certainly a natural cause of compaction, and we see it as a soil crust (usually less than 1/2 inch thick at the soil surface) that may prevent seedling emergence. Rotary hoeing can often alleviate this problem.

Tillage Operations- Continuous moldboard plowing or disking at the same depth will cause serious tillage pans (compacted layers) just below the depth of tillage in some soils. This tillage pan is generally relatively thin. It may not have a significant effect on crop production, and can be alleviated by varying depth of tillage over time or by special tillage operations.

Wheel traffic - This is without a doubt the major cause of soil compaction. With increasing farm size, the window of time in which to get these operations done in a timely manner is often limited. The weight of tractors has increased from less than 3 tons in the 1940's to approximately 20 tons today for the big four-wheel-drive units. This is of special concern because spring planting is often done before the soil is dry enough to support the heavy planting equipment.

Minimal Crop Rotation- The trend towards a limited crop rotation has had two effects:

1.) Limiting different rooting systems and their beneficial effects on breaking subsoil compaction

2.) Increased potential for compaction early in the cropping season, due to more tillage and field traffic.

Effects on Plants and Crops

• Equipment and tillage effects the soil structure, which is important because it controls the soils ability to maintain a equilibrium for water, nutrients, and air. All of these are needed for plant root activity

• Ideal Soil- roughly 50% soil particles(minerals and organic matter), 25% air space, 25% water

Advantages

• Speed up seed germination because it allows for better contact between seed and soil

• Mild to moderate compaction can prevent water from leaching through and provide new seed with moisture to germinate

• New corn planters have been modified with rollers to moderately compact soil after planted

Advantages

• Increase root branching and secondary root development because more nutrients closer i.e. phosphorous-non moving nutrient

• Reduces settling, increases stability• Helps prevents against soil settlement and

frost damage

Disadvantages

• Makes soil harder for roots to explore through, limiting nutrient intake

• Effects plants water flow and storage-very important for plants

• Erosion• Surface wetness is greater and takes longer

time to dry• Decreased plant yields-damage to above

ground parts of plants

Disadvantages

• Creates unfavorable growing conditions for roots and restricts oxygen, water, nutrient supplies

• Increases dependence on mechanical figures• Increases density, carbon dioxide amounts-toxic

to the plant, increases heat build up• Winter-kill can occur in spring due to trapping in

colder temperatures from winter season• Do not effect plant roots directly, but indirectly

Erosion

Ways Erosion Happens

• Water• Wind

Ways to Prevent Erosion

• Reduce soil compaction• Vegetation • Avoid growing crops on fields with steep

slopes.

Erosion

Erosion

Why Soil Erosion is a Problem

• Removes topsoil• Loss of natural nutrients• Loss of fertilized soil• Loss of seeds or plants• Loss of organic matter• Pesticides and fertilizers could possibly be

washed into water supplies.

Study on erosion

• Table 1. Corn and soybean yield loss in severely eroded soils compared to slightly eroded soils in

• three studies in Indiana.Three-year study Six-year study Ten-year study

Corn -16% to -34% -15% -9% to -18%

Soybeans -14% to -29% -24% -17% to 24%

Where can soil erosion happen?

• In fields that have slopes or that are in low areas.

• In fields where the soils are compacted• On athletic fields where they have compacted

soils and poor drainage• On golf courses in the bunkers and around the

cart paths.

Problems due to compaction

• Bulk Density is increased in compacted soils• Water infiltration and percolation is decreased

which can lead to standing water on the turf and cause disease to turf

• In the winter compacted soils may hold more water which can cause turf to come out of dormancy much slower because wet and damp soil warm much slower than dry soils

Problems

• Oxygen Diffusion Rate is reduce in compacted soils

• Decreased microorganism activity• Root growth can completely stop or reduced

greatly• Turf establishment rate is greatly reduce• Turf wears much faster

Symptoms of Compacted Soils

• Turf develops a shallow root system• Yellowing of turf• Turf stand can start to thin out• Weed growth and disease

Bulk Density

Effects of a compacted playing surface

• Two most important factors in athletic fields are how hard the surface is and its level of traction it provides to the athletes

• Compacted soils reduce athletic playing ability• Increases the chances of a player getting

injured

Appearance of Turf

Fixing and Preventing Soil Compaction

Soil compaction

• Soil compaction can be difficult and expensive to fix once it exists.

• Best method is to do preventative maintenance • On turf fields aeration and topdressing are used• In agricultural fields minimized traffic from

heavy machinery and utilization of weight distribution techniques can be used– No-till farming and varying conventional tillage

practices can also help

Aeration

Aeration opens the soil and helps the soil “breathe” easier and makes for healthier turf.• Two basic types of aeration– Core Aeration– Solid Tine Aeration

• When to aerate– Spring and Fall are ideal for core aeration– Summer

• There are other benefits to turf from aeration other than reduced compaction

TopdressingTopdressing adds a thin layer of soil or a prepared soil mixture to a turf grass area• Topdressing keeps the holes made in aeration

open• Best to match texture of topdressing material

with existing soil• Both aeration and topdressing can temporarily

reduce turf quality• Repeated topdressing, in conjunction with

aeration, has other benefits

Agricultural Fields

• Subsoil compaction– Reduce load– Increase number of axles

• Surface compaction– Reduce tire pressure to minimal allowable pressures– Using tracks or duals to replace singles– Using larger diameter tires to increase length of footprint

Agricultural Fields

• Avoid tillage of wet soils• Keep equipment sharp• Vary depth of primary tillage from year to year• Combine field operations to reduce traffic• No-Till– No plow pan that can be caused by conventional

tillage equipment– Cover crops used in no-till help reduce soil

compaction

Existing Compaction

• Subsoiling– Results may be temporary

• Add organic matter– Increases fertility and biological activity

• Introduce worms to the soil– Worms do be beneficial when added to soil with

mulch

History

• Since the 1800’s when Benjamin Lincoln stated that he had noticed a large decrease in plant production and growth from letting livestock wander and graze

• Horses pulling carts and wagons• Increasingly getting worse with heavier

machines and farming equipment being introduced

References

• agguide.agronomy.psu.edu/cm/sec1/sec11f.cfm

• www.sustainablehorticulture.com/compaction.htm

• American School & University, Sep99, Vol. 72 Issue 1, Sports Field Management Guide p14

• http://www.omafra.gov.on.ca/english/engineer/facts/87-040.htm

• http://soils.usda.gov/sqi/management/files/sq_atn_7.pdf