1998 Iowa Turfgrass Research Report
Managing Cool-season Grasses as Part of a SportGrass® System
David D. Minner and Jeffrey J. Salmond
New and innovative systems are being developed for natural grass fields. Coaches, athletes, and trainers prefer natural grass to reduce physical stress on players. Artificial surfaces are known for their durability and infrequent need for maintenance. SportGrassâ is the first product that combines the playability of natural grass with some of the more durable characteristics of synthetic turf.
The SportGrassâ system is a synthetically reinforced layer of grass that is grown on a sand-based rootzone. The system consists of natural grass growing in a synthetic matrix containing fibrillated fibers (polypropylene blades) attached to a backing. Within the layer of sand are polypropylene grass blades tufted into a woven backing (www.sportgrass.com). Roots can grow through the woven backing and into the sand below. Since grass roots grow down through the synthetic fibers and backing, the crown and roots of the plant are protected. SportGrassâ is horizontally and vertically stabilized by the combination of the polypropylene blades and the backing material. Grass can be established by seeding or sprigging. Specialized methods have been developed to produce, harvest, and install large-roll SportGrassâ sod.
The SportGrassâ system was designed to reduce divots, ruts, and bare spots due to heavy traffic. The product claims to reduce the need for renovation and frequent repairs. Cool-season and warm-season turfgrasses can be grown in the SportGrassâ system. If the natural grass is briefly worn away, the synthetic and sand portions of the SportGrassâ system maintain a stable playing surface. SportGrassâ also aids in a quicker recovery of the turfgrass (www.sportgrass.com).
The SportGrassâ synthetic material is typically produced in 15 ft by 100 ft rolls. The synthetic turf material is laid on top of the sand-based root zone. During installation, the seams of the synthetic material are temporarily held to the rootzone with metal sod staples. Sand that matches the root zone is then topdressed and brushed into the 3/4-inch polypropylene blade matrix. As an alternative, a gunit gun has been used to blow dry sand into the polypropylene fibers. Once the matrix has been filled, seeding or sprigging can take place. The seed is typically sliced into the surface so that the plant crown develops within the sand/fiber matrix. SportGrassâ can also be installed as sod. SportGrassâ sod is grown over a plastic sheet to impede root penetration. The sod is then sliced into appropriate sizes in the sod field (usually 42 inches by 40 feet). A large roll harvester is used to roll up the sod. SportGrassâ has been used on football, baseball, and soccer fields and golf courses.
Most natural grass systems tend to become elevated above the surface where the grass was first established. Over time the accumulation of thatch and the process of topdressing can add as much as 0.5 to 2.0 inches of material above the original soil line where the grass was first started. Stabilizing materials that were once near the surface can be lowered in the profile as organic and mineral material accumulates above the synthetic stabilizer. We are interested in finding out if this "burying" of the stabilizer material reduces their effectiveness. We also want to know if current management practices can be used to prevent accumulation of thatch above the synthetic stabilizer. Stabilizers also tend to reduce surface resilience and increase surface hardness (as measured by Gmax). Two separate studies were established in the fall of 1996 to evaluate mat management above the surface of the stabilizers and to evaluate field hardness.
Methods:
Study # 1 - Mat Management
The objective was to evaluate conventional methods of turfgrass management as they apply to SportGrassâ . Of particular interest is how grass management practices influence the accumulation of organic matter within and above the synthetically reinforced zone. Most grass systems tend to increase in elevation as topdressing, thatch, and mat accumulate above the original surface where the grass was first established. Moderate accumulation of thatch may improve surface characteristics by increasing cushion and biomas cover. Eight treatments including two non-SportGrassâ controls were used to evaluate mat management in the SportGrassâ System (Table 1a). The six SportGrassâ treatments consisted of catching clippings, returning clippings, verticutting, solid coring, Primo plant growth regulator, and verticutting after thatch accumulation. Verticutting and coring treatments were applied on 19 September 1997. Primo treatments will begin in 1998. Verticutting was applied by making two passes over the plot in opposite directions using a Bluebird vertical mower set to cut approximately 1/4-inch into the surface (even with the top of the synthetic grass blades). The thatch litter was hand raked and removed from the surface. Hollow tine coring with 5/8-inch tines was attempted on a border area containing SportGrassâ . The GA30 Cushman aerifyer with 5/8-inch hollow tines did not adequately penetrate the synthetic backing of the SportGrassâ material. Pointed 3/8-inch solid tines easily penetrated the backing and were used in the study. Holes were punched on 2-inch centers at a rate of 36 holes/sq ft.
Study #2 - Grass Species
The objective was to evaluate how grass species, seeding rates, and traffic intensity influence the performance of the natural grass and synthetic turf combination. (Tables 2a and 2b). Synthetically stabilizing sand surfaces typically increases surface hardness. In some situations synthetic stabilizers have been perceived as making fields too hard. When cleat penetration and traction are reduced the field appears slippery. Fields dominated by a thick stand of perennial ryegrass have been described as being more slippery than other types of grass. This study will evaluate the performance of a SportGrassâ system with respect to hardness and footing.
In both studies, surface hardness and traction measurements were taken on 12 November. Surface hardness was measured with a 2.25-kg hammer attached to the Bruel and Kjaer 2515 Vibration Analyzer. The hammer was dropped from a height of 18 inches. Soil moisture content was performed on five plots in the mat management study. Traction was conducted with a torque wrench apparatus attached to a cleated plate that was developed by Canaway and Bell, 1986. One hundred pounds was the load bearing weight of the torque device and the weight was dropped from a height of 2 inches. Traction was assessed as the amount of torque (N× m) required to tear the underlying sod. Traction data represent the average of three individual measurements per plot.
The Statistical Analysis System version 6.06 (SAS Institute, 1989) and Analysis of Variance (ANOVA) were used to analyze the data. Least Significant Difference (LSD) means comparisons were made to test between treatments effects on surface hardness (Tables 3 and 4) and traction (Table 3).
Results:
Study # 1 Mat Management
Information is preliminary at this time since treatments just started in 1997 and thatch may take two or more years to accumulate. However, there was a clear and significant difference in surface hardness associated with solid tine coring on 12 November 1997, 54 days after treatment (Table 3a). Solid tine coring of SportGrassâ reduced surface hardness by approximately 18g (77g for solid tine vs. approximately 95g for non-cored SportGrassâ treatments). The solid tined SportGrassâ plots had a surface hardness that was similar to the seeded or sodded non-SportGrassâ controls (Table 3a). The sodded control had a significantly higher Gmax than the seeded control.
With respect to surface hardness of SportGrassâ , the preliminary results in this study indicate that solid tine coring can be used to effectively manage surface hardness.
Traction was not affected by the treatments at this time. There was no difference in traction between SportGrassâ treatment and non-SportGrassâ treatments.
Study # 2 Grass Species
Seeding rate did not affect surface hardness, although there was a slight trend showing reduced hardness with higher seeding rates (Table 4). Perennial ryegrass alone or mixed with Kentucky bluegrass significantly reduced surface hardness compared to Kentucky bluegrass used alone.
Research will continue for two more years before a final report is prepared, however, early indications are that typical turfgrass management practices can be used to regulate surface hardness on SportGrassâ fields.
Canaway, P.M. and M.J. Bell. 1986. Technical note: An apparatus for measuring traction and friction on natural and artificial playing surfaces. J. Sports Turf Res. Inst. 62:211-214.
Table 1a. Treatments used to evaluate management of the grass mat within the SportGrassâ system.
Trt
Clippings
Cultivation
PGR
Other
with
SportGrassâ
1.
Catch
none
none
none
yes
2.
Return
none
none
none
yes
3.
Return
Verticut
none
none
yes
4.
Return
Solid core
none
none
yes
5.
Return
none
Primo
none
yes
6.
Return
none
none
after thatch accumulates, begin
thatch reduction treatment
yes
7.
Return
none
none
Seeded control
no
8.
Return
none
none
Sodded control
no
Table 1b. Plot layout for mat management study.
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ISU Horticulture:Publications:1998 Turfgrass Report | College of Agriculture |