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Traffic Stress, Thatch & Turf Cultivation

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objective

For better long-term performance, take steps to reduce traffic stress on turf areas.

Understand that traffic results in wear and compaction stress.

  • Effects from both vehicular and foot traffic are a common cause of injury to the shoots and foliage of turfgrass plants.
  • Wear damage is immediate and involves bruising and crushing injury to turfgrass shoots.
  • Compaction, which is chronic and develops over time at the root zone level, is stress caused by increases in soil hardness and the loss of valuable soil pore space.
  • Traffic stress (both wear and compaction) can cause significant losses in shoot density and vigor, and in turn can promote weed encroachment.

Plant wear and compaction tolerant grasses to alleviate losses in function and quality.

  • Wear and compaction are distinctly different stresses. Thus, selecting wear tolerant grasses does not necessarily equate to superior compaction tolerance.
  • Selecting wear tolerant grasses can help to reduce compaction tendency, however, as superior wear tolerance provides greater shoot density and cushioning to help protect the soil.
  • Selecting wear tolerant species such as perennial ryegrass does not insure wear tolerance because of the tremendous variation that typically exists among cultivars. Selecting the proper cultivar is equally important to selecting the proper species in this case.
  • Selecting wear tolerant turfgrasses is just one of several management practices important in maintaining adequate grass cover under traffic, as cultural practices such as N fertilization and irrigation can influence morphological and anatomical characteristics associated with wear tolerance as well.
Relative wear tolerance of cool-season turfgrass species.
perennial ryegrass = tall fescue > Kentucky bluegrass > bentgrass = fine fescue > annual and rough bluegrass

Figure 14. Re-route traffic or consider alternative surfaces in areas subject to heavy wear. Redirect traffic patterns regularly whenever possible to reduce wear and compaction injury.

  • Even the most wear tolerant grasses need rest to promote recovery from wear injury.
  • On residential lawns, the redirection of traffic patterns can be as simple as moving around outdoor items such as furniture or grills, or as complex as installing fencing or landscape plantings.
  • Grasses growing under low light caused by shading from tree canopies or buildings are especially intolerant of wear. Traffic should be always be minimized on such areas whenever possible.
  • In extreme cases where traffic cannot be regularly and effectively re-routed it may be necessary to consider alternative surfaces other than natural turf.

Follow a balanced fertility program to enhance wear and compaction resistance.

  • High shoot density provides cushioning and energy absorbing qualities, thereby protecting turfgrass growing points from wear injury and reducing compaction tendency.
  • Balanced nitrogen (N) input is necessary for optimum wear tolerance. Inadequately fertilized turf may not provide adequate vigor and density to maintain maximum wear tolerance.
  • Over-application of N promotes excessive shoot growth and succulent tissues that can lead to greater wear injury.
  • Apply optimum levels of potassium (K) in balance with N to maintain good plant vigor.
  • Adequate K is needed for cell wall thickening, which is important in wear tolerance.
  • For most fine textured soils K can be applied at levels that are approximately 50 to 75% of the total annual N. Higher levels of K to achieve an N:K ratio closer to 1:1 are recommended for sandy soils.

Irrigate carefully to promote the best traffic tolerance.

  • Irrigate to fully recharge the root zone and allow for mild soil drying to occur between irrigation events.  Soil drying increases compaction resistance.
  • Maintaining a moist root zone at field capacity promotes succulent tissues and greater wear injury as well as compaction tendency.
  • An irrigation regimen that that supports moderate growth is preferred.

Mow intelligently to keep up energy reserves and maintain shoot density.

  • Moderately close mowing, within the recommended range for the species and use, is preferred for maximum wear tolerance.
  • Excessively close mowing depletes energy reserves important for wear recovery.
  • Excessively close mowing can decrease shoot density and cushioning that can accelerate compaction tendency and increase injuries to turfgrass plants and end-users of the turf.

objective

Monitor and manage thatch to maximize the benefits and prevent associated problems.

Understand what thatch is and the implications of thatch layer thickness.

  • Thatch is a tightly intermingled layer of living and dead stems, leaves, and roots which accumulates between the layer of actively growing grass and the soil underneath.
  • Thatch is a normal component of an actively growing turf, and as long as it is not too thick, can provide cushioning, increase the resilience of the turf to traffic, and aid in water retention.
  • An excessive thatch layer (typically more than 1/2 to 3/4 inch, depending on the situation) can restrict the movement of air, water, fertilizer and other materials to the roots, all of which are necessary for healthy, vigorous turf growth.
  • Since thatch greatly restricts the permeability of air and water, the grass plants tend to root within the thatch in an attempt to obtain these resources. Thatch is a poor growing medium and this process reduces the overall drought resistance of the turf.
  • Thatch can harbor fungi that cause turf diseases, and can provide cover for surface-feeding insects.  To a similar end, excessive thatch can also reduce the effectiveness of pesticides for manging pest problems.
  • The overall effect of a thick thatch layer is an unthrifty lawn which does not respond well to management practices and is easily injured by adverse weather conditions and pests.

Recognize how thatch develops.

  • Actual thatch accumulation involves a balancing act between the rate that turfgrass growth adds plant material to the thatch layer and the rate at which microorganisms are able to break down that material.
  • Any factors that favor plant material turnover (e.g. high fertilizer rates, laterally spreading grasses such as Kentucky bluegrass) and/or restrict microorganism populations (e.g. compaction, excessive pesticide use) can cause thatch to build up to an undesirable level.
  • Grasses that produce large numbers of resilient secondary lateral stems, such as Kentucky bluegrass (rhizomes) and creeping bentgrass (stolons), tend to produce thatch readily.
  • Contrary to a widely-held belief, leaving grass clippings does not cause an increase in thatch buildup. In fact, this practice helps to encourage a healthy population of microorganisms that will break down clippings and thatch and return a valuable source of balanced nutrients back to the turf.
  • Good aeration, soil pH around 6.5 and adequate moisture favor the build-up and activity of beneficial microorganisms that decompose thatch.
  • Unbalanced fertilization and the indiscriminate use of fungicides and insecticides play the most havoc on these beneficial organisms, and thatch problems are sometimes common in acidic and compacted soils since a healthy microorganism population does not flourish under these conditions.

Monitor for thatch problems.

  • To examine the thatch layer, cut out a small, triangular-shaped plug of turf several inches deep.
  • If the spongy layer of material above the mineral soil is more than 1/2 inch thick when compressed, consider implementing cultural practices to encourage decomposition of the thatch layer.

objective

Include turfgrass cultivation in the management plan to manage traffic stress and thatch and improve the overall health of the turf system.

Understand how turfgrass cultivation works.

  • Cultivation in the turfgrass arena is very different than most cultivation employed in cropping systems.
  • In turf management, cultivation refers to any cultural practice that disrupts the soil surface.
  • Cultivation is used to accomplish management objectives including the management of thatch, the alleviation of soil compaction, or the promotion of seed-to-soil contact when overseeding, renovating, or making repairs.
  • Cultivation practices include but are not limited to aeration, dethatching, vigorous raking, or any other practice that disturbs the soil.
Table 20. Benefits of commonly used cultivation methods associated with thatch, compaction, and seedbed preparation.
Method Loosens thatch Reduction of soil compaction Promotion of seed-to-soil contact
None Some Significant
Power raking     Moderate
Vertical cutting     Moderate
Slicing         High
Spiking         Moderate
Hollow tine coring       High
Grooving     High
Solid tine coring       Moderate

Address soil compaction to reduce problems caused by alterations in the physical properties of the soil.

  • The decrease in total soil pore space associated with compaction can reduce drainage, reduce channels available for root growth and inhibit air exchange.
  • Compaction can decrease soil oxygen and negatively impact plant respiration and growth.
  • Compaction can alter water infiltration and percolation rates, which influence irrigation practices and scheduling.
  • Thatch is often found in association with soil compaction because of the unfavorable soil conditions for microbial activity and decomposition.

Core aerate regularly to realize several management benefits.

  • Core aeration releases built-up toxic gases, such as CO2, and allows the influx of O2 into the root zone.
  • Core aeration increases soil infiltration rates as a result of increased surface area, thereby reducing water runoff and puddling, and allows wet soils to dry faster.

Example: 1,000 square feet of turf after a single aeration event using a 3/4 inch diameter tine, spaced two inches on center, with a tine penetration depth of 2 inches, would be equivalent to 2180 square feet of surface area.

  • Enhanced rooting occurs within core aeration holes.
  • Core aeration increases plant uptake of nutrients, and promotes incorporation of immobile materials such as lime and phosphorus into the root zone.

Recognize that core aeration can be utilized to manage thatch.

  • Favorable conditions for air exchange and microbial activity following core aeration lead to accelerated decomposition and subsequent thatch reduction.
  • Heavy thatch (1/2 inch to greater than 1 inch or more) should be removed by verticutting or power raking prior to core aeration.
  • Substantial amounts of thatch can be physically removed by core aeration when thatch-containing plugs are collected and removed. The extent of thatch removal will vary with tine diameter, tine spacing, and number of passes but can be as much as 10% or more.
  • Moderate levels of thatch (1/3 to 1/2 inch or less) can be maintained by regular aeration and dragging and returning broken plugs.

Consider additional factors for effective core aeration.

  • Consider aerator tine length, diameter and spacing. The more cores removed per square foot of compacted soil and the greater the penetration depth, the greater the benefit in alleviating compaction and promoting rooting and gas exchange.
  • Avoid core aeration when compacted soils are dry which can increase machine stress and severely limit aeration effectiveness.
  • Consider irrigating the soil before aeration to the desired depth of penetration to ease soil strength and tine resistance, but avoid core aeration when the soil is too wet which can be counterproductive and increase soil compaction.
  • Take care not to damage components of any underground irrigation system during the aeration process.

Give appropriate attention to cultivation timing and frequency for maximum benefit.

  • Cultivation practices are disruptive and should be timed to allow for an adequate period for plant recovery. Whenever possible, cultivation operations should be performed just before or during peak the shoot and root growth periods in spring and late summer/early fall.
  • Late summer/early fall cultivation is preferred where crabgrass and other annual weeds are a problem (most residential lawns in the Northeast).  Spring and early summer cultivation is preferred to fall where annual bluegrass infestation is a problem (many athletic fields and golf courses).
  • Late summer cultivation is preferred when combined with overseeding, fertilization, and liming programs.
  • Mid-summer aeration should be avoided because of the potential for excessive soil drying and possible spread of diseases.
  • Heavily trafficked sites (paths, areas that receive vehicle traffic, etc.) may be aerated 4 to 6 times per year depending on the soil type and the extent of traffic.
  • Most lawn areas that receive little traffic will generally benefit from at least one core cultivation event every year or two, depending upon site conditions and specific management objectives.

Topdressing following cultivation practices can promote a more uniform surface.

  • Topdressing is a useful practice to even out bumpiness and fill in core aeration holes or slits from dethatching operations.
  • Lawns can be topdressed with approximately 1/8 inch of topsoil similar to that found in the existing root zone, or with an appropriate compost or similar material.
  • Effective topdressing requires detailed knowledge of physical and chemical properties of both topdressing material and existing soil.
  • Using an inappropriate topdressing material often results in negative benefit, as dissimilar topdressing materials will not interact well with the existing soil.
  • Addition of peat and other organic materials also must be done with care, as some materials can simulate thatch and incite similar turf problems.
  • Topdressing materials should be tested for physical and chemical properties, and results should be kept on file.