9. Traffic Stress & Turf Cultivation

OBJECTIVE: For 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 primary 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 refers to stress caused by increases in soil hardness. Compaction is chronic and develops over time at the root zone level. 
• 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. 
• Selecting wear tolerant turfgrass 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. 

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. 
• Grasses growing under low light caused by shading from tree canopies or buildings are especially intolerant of wear. Traffic should be redirected away from such areas. 
• 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 the 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. 
• Optimum levels of potassium (K) are needed that are in balance with N to maintain good plant vigor. 
• Adequate K is needed for cell wall thickening 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 for a N:K ratio closer to 1:1 are recommended for sandy soils. 

Irrigate judiciously 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 moist root zones at field capacity promotes succulent tissues and greater wear injury as well as promoting compaction tendency. Irrigation that provides moderate growth is preferred. 

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

• Moderately close mowing 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 endusers of the turf. 

OBJECTIVE: Include turfgrass cultivation in the management plan to promote the overall health of the turf system. 

Understand turfgrass cultivation. 

• Cultivation in the turfgrass arena is somewhat different than cultivation employed in cropping systems. 
• In turf management, cultivation refers to any cultural practice that disrupts the soil surface.  
• Cultivation practices include but may not be limited to aeration, dethatching, hard raking, or any other practice that opens the soil. 

Manage 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 infiltration and percolation rates, which alters 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 for 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 allowing wet soils to dry faster. 

Example: 1,000 square feet of turf after a single aeration event using a ¾ 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. 

Monitor for thatch 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. 
• 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 ½ inch thick when compressed, consider implementing cultural practices to encourage decomposition of the thatch layer. 
• Practices which discourage thatch build-up include frequent mowing, retention of clippings, reducing fertilization, and maintain pH at approximately 6.5. 
• Mechanical methods to reduce and remove thatch include core aeration, verticutting, dethatching and power raking. 

Utilize core aeration to manage thatch. 

• Favorable conditions for air exchange and microbial activity following core aeration lead to accelerated decomposition and subsequent thatch reduction. 
• Heavy thatch (½ 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 (⅓ to ½ inch or less can be maintained by regular aeration and dragging and returning broken plugs. 

Table 17. Benefits of commonly used cultivation methods associated with thatch, compaction, and seedbed preparation. 
(KEY: ♦ = yes, without indicating any level; ♣ = to some extent; ♠ = to a major extent).

Method	Loosens thatch	Reduction of soil compaction			Promotes seed/soil contact
		None	Some	Significant
Power raking	♦	♦			♣
Vertical cutting	♦	♦			♣
Slicing
Spiking					♣
Hollow tine coring				♦	♠
Grooving	♦			♦	♠
Solid tine coring			♦		♣

Give appropriate attention to core aeration timing and frequency for maximum benefit. 

• Aeration should be timed to allow an adequate period for plant recovery. Whenever possible, cultivation operations should be performed during peak shoot and root growth periods of early spring and early fall. 
• Spring and early summer cultivation is preferred to fall when annual bluegrass infestation is a problem. Fall cultivation is preferred when crabgrass is a problem. 
• Fall core aeration is preferred when combined with fall overseeding, fertilization, and liming programs. 
• Mid-summer aeration should be avoided because of the potential for excessive soil drying and the 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 which receive little traffic will generally benefit from at least one or more core cultivations every year or two, depending upon site conditions and specific objectives. 

Topdressing following cultivation practices can promote a more uniform surface. 

• Lawns can be topdressed with approximately ⅛ inch of topsoil similar to that found in the existing root zone, or with an appropriate compost or similar material to even out bumpiness and fill in core aeration holes or slits from dethatching operations. 
• 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. 

Consider additional factors for effective core aeration. 

• Consider aerator tine length, diameter and spacing. The more core aerifier holes 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 counter productive and increase soil compaction. 
• Take care not to damage any parts of the irrigation system during the aeration process.