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Understanding Soil Compaction

Understanding Soil Compaction. April 27, 2016 Steven E. Yergeau, Ph.D. Environmental & Resource Management Agent, Ocean & Atlantic Counties Rutgers Cooperative Extension of Ocean County. Outline. What is soil compaction? What causes soil compaction? How does compaction affect soil health?

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Understanding Soil Compaction

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  1. Understanding Soil Compaction April 27, 2016 Steven E. Yergeau, Ph.D. Environmental & Resource Management Agent, Ocean & Atlantic Counties Rutgers Cooperative Extension of Ocean County

  2. Outline • What is soil compaction? • What causes soil compaction? • How does compaction affect soil health? • Physical properties • Biological properties • How is soil compaction managed? • How is it assessed? • What do I need from you?

  3. Introduction What is soil compaction? • Two perspectives: • Engineering • Environmental

  4. Engineering • Soil compaction is defined as an increase in density, due to an outside force, and a reduction to smaller-sized pore spaces within the soil matrix because of the removal of air from the soil. Soil becomes “densified through external compactive effort.”

  5. Engineering • Many types of construction, such as dams, retaining walls, highways/roads, and building foundations, require additional soil, or fill. This fill needs to be compacted. • The objective of compaction is to stabilize soils and improve their engineering behavior. • Reasons for soil compaction during construction: • Decrease future settlement of the soil • Increase the amount of the stress that a soil can sustain • Decrease permeability

  6. Engineering

  7. Engineering

  8. Environmental • Soil compaction is defined as an increase in soil bulk density. • Compaction is the loss of air from pore spaces in the soil over a long period of time.

  9. Environmental

  10. Undisturbed Lands: Forests & Woodlands 1.03g/cm3 Residential Neighborhoods 1.69 to 1.97g/cm3 Concrete 2.2g/cm3 Environmental Golf Courses, Parks, & Athletic Fields 1.69 to 1.97g/cm3

  11. Environmental Surface compaction Subsoil compaction

  12. WHAT CAUSES SOIL Compaction?

  13. Causes of Compaction • Compaction is caused by wheel or foot traffic on the soil. • For agriculture, this includes livestock traffic. • Soil is most compactable at a moisture content approximating field capacity (soil pore spaces about ½ filled with water and ½ with air). • If the soil is saturated, it is difficult to compact because water fills the pore spaces. • If the soil is too dry, there’s too much air to remove.

  14. Causes of Compaction

  15. Causes of Compaction

  16. Causes of Compaction The risk of soil compaction from agriculture is greater today than in the past due to an increase in the size of farm equipment.

  17. Causes of Compaction • For residential lawn care, 1 hour of lawn mowing equals 20 miles driven.

  18. Causes of Compaction Wetter soils will transmit pressure lower and create deeper compaction. The heavier the load, the deeper compaction will become.

  19. Causes of Compaction • Compaction can also be inherent in soils due to natural properties of those soils. • Water content • (% water) • Depth to water table • Soil texture (fine, moderately coarse, coarse grained)

  20. WHAT are the effects oF Compaction?

  21. Effects of Compaction Physical Properties: • Compacted soil is dense and has low porosity. • Infiltration is then reduced and erosion is increased.

  22. Effects of Compaction H2O H2O Non-Compacted Compacted

  23. Effects of Compaction Physical Properties: • Compacted soil is dense and has low porosity. • Infiltration is then reduced and erosion is increased.

  24. Effects of Compaction • Physical Properties: • Compaction causes the penetration resistance of the soil to increase with increasing density. There is little root growth through soil above 300 psi, except if there are cracks and macropores in the soil that can be followed by plant roots.

  25. Effects of Compaction Biological Properties: Compaction affects nutrient uptake: • Denitrification (creation of nitrogen gas) can increase in compacted soil due to limited aeration. • Phosphorus and potassium uptake can be reduced if root growth is inhibited.

  26. Effects of Compaction • Biological Properties: • Compaction reduces productivity: • Compacted soils inhibit the growth of plant roots affecting the health of crops, pastures, and landscape vegetation. • Research in tilled soils showed losses due to compaction. From: Soil Fertility and Compaction - http://www.cropnutrition.com/soil-fertility-and-compaction

  27. Effects of Compaction • Biological Properties: • Compacted soil is a harsher environment for soil organisms (especially earthworms) to live in.

  28. Mitigating Compaction Compaction can be managed (never eliminated) in a variety of ways: • Do not use heavy machinery on wet soils; wait for soils to dry before driving or walking over them. • Restrict or redirect foot traffic; line paths with stone, mulch, or pavers. • Aerate the soil to help improve nutrient availability to plants. • Mechanically break up compacted soils; hand dig or use a tiller to fracture soils. • Remove and replace topsoil. • Create raised beds for plantings. • Plant deep rooting vegetation prior to compaction creation; plant after compaction occurs.

  29. Mitigating Compaction Tillage radish (Daikon)

  30. WHAT ARE SOME OF THE SIGNS OF COMPACTION?

  31. Compaction – What to Watch • High traffic areas and foot paths • Areas of exposed soil

  32. Compaction – What to Watch • Surface/shallow roots • Areas where no plants grow

  33. Compaction – What to Watch • Areas where water ponds at surface

  34. Compaction – What to Watch Portion of the New Jersey Soil Health Assessment Guide (available in its entirety at http://www.soildistrict.org/wp-content/uploads/2012/07/NJSoilHealthAssessmentGuide.pdf)

  35. Assessing Compaction Penetrometers • The force required to push a rod into the soil is a measure of soil strength. • Penetrometers are devices used to measure the resistance of a soil to penetration to estimate the effect of compaction on growth, and to detect layers of different soil strength.

  36. SOIL COMPACTION ASSESSMENT PROCEDURE

  37. Where to Sample Only sample turf areas of your yard.

  38. When to Sample Sample 2-3 days after a rain storm.

  39. How to Sample • Inspect the dial at the top of the tester to make sure it is set at 0 psi. • Remove the locking ring by unscrewing the nuts from the ring with an adjustable wrench and sliding the ring off of the penetrometer.

  40. How to Sample • Install the ½ inch tip by screwing it onto the end of the soil compaction tester. • Ensure that the rubber o-ring is at the end of the rod where it meets the ½ inch tip.

  41. How to Sample • Grab the penetrometer by the handles and insert the pointed end of the rod into the soil. • Apply even pressure to the handles on the instrument to keep the rod point penetrating the soil at a slow and even pace. Be sure to keep the instrument as vertical as possible.

  42. How to Sample • Push the penetrometer into a random location in your yard until the gauge reads 300 psi, then stop. NOTE: The inner ring of the gauge is read when the ½-inch tip is installed.

  43. How to Sample • Measure the distance that the rod has penetrated into the soil from the end of the ½ inch tip of the instrument to the point on the rod where the rubber o-ring has stopped. • Record the depth (in inches) on the data sheet. • Carefully wipe off the instrument with a rag or paper towel before taking additional measurements.

  44. How to Sample • Reset the o-ring by sliding it to the end of the rod where it meets the ½ inch tip. • Take depth measurements in a minimum of ten locations in your yard.

  45. How to Sample • When ten measurements are completed, remove the ½ inch tip and the rubber o-ring from the penetrometer. • Reattach the locking ring by sliding it all the way to the top of the rod and tightening the nuts with the adjustable wrench.

  46. How to Sample • Take a composite soil sample, by gathering several small soil samples from random spots in your yard and combining them into the sampling bag. Take samples from just below the turf roots. • Return all equipment, the data sheet, and the soil sample bag to the office.

  47. Questions? Steven E. Yergeau, Ph.D.Rutgers Cooperative Extension of Ocean County1623 Whitesville RoadToms River, NJ 08755(732) 505-3671yergeau@njaes.rutgers.eduocean.njaes.rutgers.edu

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