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. SportGrass is the first product that combines the playability of natural grass with some of the more durable characteristics of synthetic turf.

The SportGrass 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. SportGrass 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 SportGrass sod.

The SportGrass 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 SportGrass system. If the natural grass is briefly worn away, the synthetic and sand portions of the SportGrass system maintain a stable playing surface. SportGrass also aids in a quicker recovery of the turfgrass.

The SportGrass 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. SportGrass can also be installed as sod. SportGrass 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. SportGrass 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.

The objective was to evaluate conventional methods of turfgrass management as they apply to SportGrass. 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 biomass cover. Eight treatments including two non-SportGrass controls were used to evaluate mat management in the SportGrass System (Table 1a). The six SportGrass treatments consisted of catching clippings, returning clippings, verticutting, solid coring, Primo plant growth regulator, and verticutting after thatch accumulation. Verticutting was applied on 4 May 1998 and 6 May 1999. Solid tine aerification was applied on 4 May and 25 August 1998 and on 6 May and 25 August. Primo treatments were applied on 23 May, 27 June, and 29 July 1998 and on 20 May, 28 June, and 27 July 1999. Verticutting was applied by making two passes over the plot in opposite directions using a Bluebird vertical mower. The verticut depth was set so that it just touched 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 SportGrass. The GA30 Cushman aerifyer with 5/8-inch hollow tines did not adequately penetrate the synthetic backing of the SportGrass 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. Heavier coring equipment such as the Cushman GA60 have successfully hollow cored through the SportGrass backing using 3/4-inch tines.

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 evaluates the performance of a SportGrass system with respect to hardness and footing.

Studies were evaluated for turf appearance, surface hardness, and traction measurements. 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. 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. Traffic was applied during the spring and fall to simulate athletic activity. A model T224 Brouwer roller that has been converted into a riding traffic simulator was used. Both of the two-foot-wide rollers on the traffic simulator are fitted with 5/8-inch football cleats on 2-inch centers. The rollers are attached by chain and sprocket to supply a differential-slip-type of traffic that produces a tearing action of the grass surface.

The Statistical Analysis System version 6.12 (SAS Institute, 1996) 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 traction (Table 4).

At this time, results from only the mat management study will be presented. Surface hardness for treatments with SportGrass were significantly harder than the seeded and sodded control (Table 3). The only exception was that the use of solid tine aerification produced similar results to the seeded control on 14 June and 22 July (Table 3). Traction increased for all treatments with SportGrass compared to the seeded and sodded control on 6 May and 22 July (Table 4). Vertical mowing provided similar traction compared to the seeded and sodded controls (Table 4). No differences were seen on 7 Dec. for surface hardness and traction (Table 3 and Table 4)

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 SportGrass system.

Table 1b. Plot layout for mat management study.

Table 2a. Species layout for grass species study.

² ‘Pinnacle’ Perennial ryegrass

Table 2b. Plot plan of treatment arrangements for the grass species study.

Table 3. Surface hardness (g_max) of eight treatment in the mat management study on six dates during 1999. Surface hardness was measured as the peak deceleration of five separate location drops with a 2.25-kg hammer.