Treating Soil Compaction around trees & turf

However, below 12” the compaction level was the same for all of these methods (1.50 g/cm³). Plowing is most effective in removing surface compaction in these studies. Wheel traffic during the growing season increased the bulk density to 1.55 g/cm3 in the surface foot the following season. Where no tillage was done, freezing and thawing over winter reduced the bulk density only slightly and only above the 6-inch depth. In this study, disk treatments were less effective than plowing. These results confirm that freezing and thawing alone may not remove compaction.

Controlling Wheel Traffic in Ag Fields
In a normal year, as much as 90% of the field may be tracked by equipment (Figure 1). The philosophy behind controlled traffic is to restrict the amount of soil traveled on by using the same wheel tracks. Seventy to 90 percent of the total plow layer compaction occurs on the first trip across the field. By controlling traffic, the tracked area will have a slightly deeper compaction but the soil between the tracks will not be compacted (Figure 2).

Figure 1. Field coverage by normal annual field operations.

Figure 2. Field coverage in a controlled traffic situation.

There are occasional reports of adverse effects on plant growth where the wheel tracks are on both sides of the row, but even then the damage is confined to certain rows. Benefits to controlled traffic, using permanent compacted lanes, are improved tractor efficiency and floatation, less powerful machinery needed, and improved timeliness of operations.

Soil compaction in turf occurs primarily from foot traffic. Athletic training fields are especially susceptible from the near daily usage and greater weight of athletes. Recreational fields that receive almost unlimited play also must contend with vehicular traffic from mowing, periodic topdressing, and fertilizing procedures that require heavy machinery that adds to the sources of compaction.

Soil compaction it is most acute on wet soils. Water lubricates the soil, allowing the soil particles to slide past each other compared to when soil is dry. This is amplified for soils high in silt or clay and during construction. Fine textured soils remain wet longer following rain.

Preventing Compaction on Play Fields

Fields can be constructed with sand that does not compact but this is very expensive. It involves replacing existing soisl with pre-approved sand-based rootzone mixes that balances good water management and compaction prevention.

More commonly compaction in turf areas is modified by aerification techniques. These are designed to physically alter the soil profile, by removing small cores of soil or by altering the soil structure. Many approaches are available.

Hollow Tine Aerification
The most popular method is hollow tine aerification. This consists of hollow tubes 1/2 to 3/4-inch in diameter and 3 to 12-inches long, that pull out soil plugs intended to reduce the quantity of soil per unit area. In principle with less soil present the bulk density should drop. However, hollow tine aerification tends to disrupt the turf surface and the equipment is expensive, typically requiring a medium sized tractor (see below).

Solid Tine Aerification
Less soil disruption occurs with solid tine aerification. Solid tines enter the soil vertically to disrupt the soil structure. Since solid tines do not remove soil cores as do hollow tines, less clean up is necessary, reducing labor costs, and keeping playing surfaces smooth. However, the effectiveness of solid tines may be less as they do not tend to reduce the bulk density of the soil.

Deep Tine Aerification and Spiking

A modification of hollow and solid tine aerification are deep tine aerification and spiking. Deep tine aerifiers use hollow and solid tine aerifiers that penetrate to at least 12 inches. Spiking is a form of solid tine aerification utilizing thinner and shorter tines. It is used where the surface of the turf must receive as little disturbance as possible.

Drill-n-Fill

Another technique that involves a drilling method is drill-n-fill. The machinery has drill bits that are literally drilled into the ground, to create deep holes. This process brings some of the soil up to the surface and lowers bulk density. While the amount is less than the quantities for hollow tine aerifiers it causes less surface disruption because the soil brought up is powdered. However, drill-n-fill machines are slow compared to other aerifiers (see results below)

Hydroject
The hydroject uses extremely fine, high-pressure jets of water at 2000 psi that penetrate to a depth of 8 inches. The water relieves compaction, redistributes organic matter in the soil, and wets the hydrophobic spots that can occur in cultivated turf. The beauty of this systems is that treated fields exhibit no surface disturbance. However, the machines are expensive to purchase and must be carefully maintained (see below).

Slicing
Slicing uses a rolling blade to cut slits into the soil. It breaks up compaction and opens up the soil surface. Slicing also helps soil water and air exchange and slices algae and turfgrass runners. Slicing blades are continuous or consist of a series of teeth set on a rotating blade (see below).

Grooming
Grooming is similar to slicing using tiny blades attached to a walk-behind mower. Grooming is done to prevent the formation of mat and grain on fine turfgrass situations. The blades revolve against the direction of the mower. Grooming does not effect deep compaction but does prevent compaction in the upper soil profile (see below).

Reducing Compaction Around Trees

When attempts are made to preserve mature trees in construction sites the area beneath trees and surrounding areas should be covered with 6 to 10 inches of a wood-chip mulch to reduce direct pressure form construction machinery wheel traffic. Upon completion of construction this material can be scraped away or incorporated into the soil prior to replanting. In soils that are already compacted, soil can be cultivated with a plow or subsoiler or be excavate and set back for later replacement. Prior to tree planting, final grading should be done by hand or with small machinery on low-pressure tires to minimize further compaction. This is the best time to incorporate high quality, coarse grade compost, supplementary fertilizers and soil amendments. To correct compaction near trees requires techniques that will not cause damage to the root system.

Drill-hole soil replacement
This method utilizes a drill bit 2 to 4 inches in diameter and 8 to 10 inches deep, to place holes at 1.5- by 1.5-foot spacings around a tree. The holes are filled with a combination high quality compost, soil inoculants and fertilizer. Roots next to the drilled holes will respond to this by producing fine roots that grow into the drill holes. This treatment has a relatively small effect on the overall soil bulk density because the number of 6 inche deep, 2-inch-diameter holes used on a 1000 square foot area would only replace about 5 cubic feet of soil. A 4-inch-diameter hole would replace about 20 cubic feet of soil. While better it only accounts for a small portion of the total area. Some hold that this technique is less effective than other techniques.

Off course it is possible to go overboard using the device shown below!

Compressed-air treatments
High pressure air injection devices are now available that deliver large quantities of air per minute at a pressure of 100 to 300 psi. This air will lift the soil surface by up to a foot, giving the effect of an earthquake in progress. This treatment can be used alone or be followed by an injection of fill material to reduce the settling back into the open cracks. Fill materials include peat, Styrofoam, porous ceramics or activated charcoal. Fertilizers can also be added that are specially formulated for this purpose. Compressed air treatment can improve large areas up to 50 square feet per injection. Inserting the probe at 10- by 10-foot spacings can improve 500 of every 1,000 square feet treated. However, the soil fractures created exhibit a saucer-shaped opening in fine-textured soils where fill material can not keep the void space open even in small fractures near the injection site. Air fracturing affects only about 0.5 inch around the fracture line resulting in about 20 cubic feet of 1,000 square feet of treated soil. Some feel that this is too small a volume to cause a significant decrease in bulk density. However, positive effects are usually observed. Photo below shows an air gun in use.

Radial-trenching
Radial trenching involves the digging of small trenches that radiate out from the trunk. Begin the trench near the dripline of the tree and trench to the trunk to no closer than 6 inches for each inch of trunk diameter. For example, you should stay 10 feet away from the trunk of a 20-inch-diameter tree. On newly planted trees, trenches can go right up to the root ball if roots have not yet grown out. If root larger than one inch in diameter are encountered, do not cut them. No one is sure what the ideal trench width is, : Trench widths from 4 to 24 inches and depths of 12 to 18 inches have been used. The trenches should be backfilled with native soil mixed with good quality compost. If successful the new root growth into the trenches can be greater than roots growing into surrounding soil after two years.

Recently transplanted trees in compact soils that have poor root systems may improve with more drastic soil cultivation treatments. Small sample holes both in- and outside the root ball should be made to ensure that live roots are in the root ball and backfill but not in the native soil. In highly compacted soils this difference should be visible in the sample holes. Soil cultivation is then recommended, however, this treatment can harm large, established trees.

Start by applying 2 inches of compost in a circle around the root ball. The size of the circle depends on how long you intend for the treatment to benefit root growth. Healthy root growth averages about 18 inches per year. Thus, an effective treatment for 2 to 3 years should have a circle width of 3 to 4.5 feet. Add slow-release fertilizer to the surface of the compost and till into the soil down to 4 to 6 inches. This treatment is often successful but it cannot be repeated because roots will inhabit the treated area.

Application of a mulch layer is a low cost method that can be benefit trees on compacted sites, even in the absence of other treatments. Apply a mulch layer about 2 inches thick near the trunk and out to the drip line. Never place mulch directly against the trunk. Reapply mulch each year as necessary. Over the years the mulch will protect against additional compaction and give organic matter for soil development. Do not expect rapid results. However, such treatments will greatly aid trees during periods of drought.

Soil Compaction Part 2: Treatments

Reducing Soil Compaction Around Trees and Turf

Subsoiling
In the Midwest, research results evaluating the effects of subsoiling have shown few positive yield responses to subsoiling. When they do occur, they are variable and relatively small. .

Soil Compaction Part 2: Treatments

Reducing Soil Compaction Around Trees and Turf

Subsoiling In the Midwest, research results evaluating the effects of subsoiling have shown few positive yield responses to subsoiling. When they do occur, they are variable and relatively small. .

Subsoiling
In the Midwest, research results evaluating the effects of subsoiling have shown few positive yield responses to subsoiling. When they do occur, they are variable and relatively small. .