1999 Iowa Turfgrass Research Report

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

The sportsgrass™ 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.sportsgrass™.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. sportsgrass™ 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 sportsgrass™ sod.

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

The sportsgrass™ 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. sportsgrass™ can also be installed as sod. sportsgrass™ 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. sportsgrass™ 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 sportsgrass™ . 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-sportsgrass™ controls were used to evaluate mat management in the sportsgrass™ System (Table 1a). The six sportsgrass™ 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 was aerified on both 4 May and 25 August 1998. Primo treatments were applied on 23 May, 27 June, and 29 July 1998. 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 sportsgrass™ . The GA30 Cushman aerifyer with 5/8-inch hollow tines did not adequately penetrate the synthetic backing of the sportsgrass™ 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 sportsgrass™ backing using 3/4-inch tines.

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

Studies were evaluated for turf appearance, surface hardness, and traction measurements from May through October 1998. Turf appearance was evaluated by determining turf quality, turf color, and percent cover on 4 May and 16 October 1998. On five different dates, 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. Also, surface hardness was measured with a 0.5-kg Clegg impact hammer. 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. From mid-August through October, traffic was applied every Monday, Wednesday, and Friday with a model T224 Brouwer Roller that has been converted into a riding traffic simulator. 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. During 1998, all sportsgrass™ treatments received a total of 133 passes of simulated traffic. Soil moisture content was performed by randomly sampling soil cores from each study area on data collection dates.

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).

1997 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 sportsgrass™ reduced surface hardness by approximately 18g (77g for solid tine vs. approximately 95g for non-cored sportsgrass™ treatments). The solid tined sportsgrass™ plots had a surface hardness that was similar to the seeded or sodded non-sportsgrass™ controls (Table 3a). The sodded control had a significantly higher Gmax than the seeded control.

With respect to surface hardness of sportsgrass™ , 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 sportsgrass™ treatment and non-sportsgrass™ 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.

1998 Results:

Study # 1 Mat Management

Solid tine coring produced a reduction in surface hardness in both 1997 and 1998 (Tables 5 and 7). In contrast verticutting produced an increase in surface hardness in both years (Table 5). Primo had no effect on surface hardness but did produce turf with better color and quality (Table 10a).

Study # 2 Grass Species

Traffic treatment was more detrimental to perennial ryegrass than Kentucky bluegrass. On 16 October 1998, following approximately two months of simulated traffic, perennial ryegrass had 60% turf cover while Kentucky bluegrass had 97% turf cover (Table 10b). The ryegrass was showing severe cleat marks every two inches and exposed soil while the Kentucky bluegrass had only a few cleat marks and no exposed soil.

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 sportsgrass™ fields. Additional research will include soil physical characteristics and root sampling above and below the synthetic layer.

Literature Cited

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 sportsgrass™ system.

Trt	Clippings	Cultivation	PGR	Other	with sportsgrass™
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.

extra plot	extra plot	6	2	4
3	5	2	5	1
4	6	1	3	6
1	3	2	5	4
7	8	7	8	7
GRASS SPECIES STUDY AREA   North ´

Rep 1

Rep 2

Rep 3

Table 2a. Species layout for grass species study.

Trt	Grass species (whole plot trt)	Seeding rate lb/1000 ft2	Traffic Intensity (Split plot)
			Low	High
1.	Kentucky bluegrass1	2	yes
2.	Kentucky bluegrass	2		yes
3.	Kentucky bluegrass	4	yes
4.	Kentucky bluegrass	4		yes
5.	Perennial ryegrass2	7	yes
6.	Perennial ryegrass	7		yes
7.	Perennial ryegrass	14	yes
8.	Perennial ryegrass	14		yes
9.	KB & PR	2 & 7	yes
10.	KB & PR	2 & 7		yes
11.	KB & PR	4 & 14	yes
12.	KB & PR	4 & 14		yes

¹ 'Limousine' Kentucky bluegrass

² 'Pinnacle' Perennial ryegrass

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

MAT MANAGEMENT STUDY AREA     North ´
REP 1						REP 2
1	2	3	4	5	6	7	8	9
1 (1a)	3 (2a)	5 (3a)	7 (4a)	9 (5a)	11 (6a)	1 (1a)	7 (4a)	9 (5a)
10	11	12	13	14	15	16	17	18
2 (1b)	4 (2b)	6 (3b)	8 (4b)	10 (5b)	12 (6b)	2 (1b)	8 (4b)	10 (5b)
REP 3
19	20	21	22	23	24	25	26	27
7 (4a)	5 (3a)	11 (6a)	3 (2a)	1 (1a)	9 (5a)	5 (3a)	11 (6a)	3 (2a)
28	29	30	31	32	33	34	35	36
8 (4b)	6 (3b)	12 (6b)	4 (2b)	2 (1b)	10 (5b)	6 (3b)	12 (6b)	4 (2b)

Table 3a. Surface hardness and traction measurements for the mat management study on 12 November 1997. Three traction measurements were taken within each plot and averaged.

Treatments	Surface hardness (gmax) 2.25-kg hammer	Traction (N/ m)
1. Catch clippings	94.4	65.2
2. Return clippings	95.3	68.5
3. Verticut (prevent thatch)	94.3	67.3
4. Solid tine aerify	77.6	67.5
5. PGR (Primo)	93.5	67.0
6. Verticut (after thatch accumulates)	97.3	67.0
7. Control seeded	73.3	63.6
8. Control sodded	83.5	63.1
LSD(0.05)	10.0	NS

NS = not significant at P æ 0.05.

Table 3b. Percent soil moisture and organic matter (by weight).

Treatment	Rep	Sample description	% soil moisture		% organic matter
extra plot		fibers in sample	3.4		0.7
8	3	fibers in sample	3.1		0.7
7	1	seeded KB	3.3		0.5
7	2	seeded KB	4.4		0.7
7	3	seeded KB	3.0		0.7

Table 4. Surface hardness measurements taken on 12 November 1997 on the grass species study. The a and b parts of the individual plots were combined as an overall plot and surface hardness was performed.

Treatments	Seeding rate lb/1000 sq.ft.	Surface hardness (gmax)
1. Kentucky bluegrass1	2	92.8
2. Kentucky bluegrass	4	88.2
3. Perennial ryegrass2	7	81.0
4. Perennial ryegrass	14	76.1
5. KB1 + PR2	2 + 7	78.5
6. KB + PR	4 + 14	77.4
7. KB Control seeded	4	73.3
8. KB Control sodded	--	83.5
LSD(0.05)		6.1

¹ 'Limousine' Kentucky bluegrass

² 'Pinnacle' perennial ryegrass

Table 5a. Surface hardness and traction measurements for the mat management study on 4 May 1998. Three traction measurements were taken within each plot and averaged.

Treatments	Surface hardness (gmax) 2.25-kg hammer	Surface hardness (gmax) .5-kg hammer	Traction (N× m)
1. Catch clippings	75.3	56.7	68.0
2. Return clippings	73.0	60.1	66.5
3. Verticut (prevent thatch)	75.7	63.4	71.0
4. Solid tine aerify	69.1	64.3	71.3
5. PGR (Primo)	70.7	61.2	70.5
6. Verticut (after thatch accumulates)	73.9	63.2	69.8
7. Control seeded	56.9	64.8	69.7
8. Control sodded	53.2	55.3	68.0

Treatments	Surface hardness (gmax) 2.25-kg hammer	Surface hardness (gmax) .5-kg hammer
3. Verticut (prevent thatch)	94.3	108.8
4. Solid tine aerify	70.4	58.1

Treatments	Surface hardness (gmax) 2.25-kg hammer	Surface hardness (gmax) .5-kg hammer	Traction (N× m)
1. Kentucky bluegrass1	63.1	49.0	69.2
2. Kentucky bluegrass	63.6	57.7	65.8
3. Perennial ryegrass2	63.6	60.4	66.0
4. Perennial ryegrass	64.2	61.3	66.8
5. KB1 + PR2	62.7	61.6	66.5
6. KB + PR	63.8	65.8	65.7

¹ 'Limousine' Kentucky bluegrass

² 'Pinnacle' perennial ryegrass

NOTE: On 4 May 1998 all plots for mat management and grass species studies were rated for turf quality, color, and % cover.

Quality All plots = 9 (9 = best quality)

Color All plots = 9 (9 = best color)

% Cover All plots = 99% (99% = best cover)

Table 7a. Surface hardness measurements(g_max) for the mat management study on four different dates in 1998 using a 2.25 kg hammer.

Treatments	July 24	August 25	September 29	October 29
2. Return clippings	98.7	95.0	104.4	109.0
3. Verticut (prevent thatch)	99.5	95.7	101.6	113.1
4. Solid tine aerify	94.8	89.6	94.8	101.9
5. PGR (Primo)	97.7	92.1	99.7	107.8
7. Control seeded	86.7	84.3	90.7	90.3
8. Control sodded	81.2	72.8	78.7	75.6

Table 7b. Surface hardness measurements for the mat management study on four different dates in 1998 using a .5 kg hammer.

Treatments	July 24	August 25	September 29	October 29
2. Return clippings	107.5	106.2	98.1	115.3
3. Verticut (prevent thatch)	118.2	107.9	98.9	124.9
4. Solid tine aerify	115.5	100.7	100.5	116.1
5. PGR (Primo)	107.8	101.8	97.3	111.9
7. Control seeded	129.7	102.8	96.1	113.5
8. Control sodded	114.7	103.9	94.2	98.5

Table 7c. Traction measurements(N× m) for the mat management study on four different dates in 1998. Three traction measurements were taken within each plot and averaged

Treatments	July 24	August 25	September 29	October 29
2. Return clippings	73.0	66.3	61.7	59.8
3. Verticut (prevent thatch)	71.7	71.0	63.3	61.8
4. Solid tine aerify	75.0	68.3	61.0	57.2
5. PGR (Primo)	74.7	70.0	64.0	62.3
7. Control seeded	66.5	69.3	66.3	56.2
8. Control sodded	62.8	67.8	62.0	57.0

Table 7d. Surface hardness and traction measurements for the mat management study on 25 August 1998 after specific management practices were performed.

Treatments	Surface hardness (gmax) 2.25-kg hammer	Surface hardness (gmax) .5-kg hammer	Traction (N× m)
4. Solid tine aerify	66.2	84.0	65.3

Treatments	July 24	August 25	September 29	October 29
1. Kentucky bluegrass1	96.6	91.0	97.0	103.8
2. Kentucky bluegrass	99.7	89.3	96.9	104.5
3. Perennial ryegrass2	86.2	81.8	85.5	90.6
4. Perennial ryegrass	83.0	78.7	85.0	89.1
5. KB1 + PR2	83.7	77.1	85.0	90.8
6. KB + PR	81.7	81.1	86.5	91.1

¹ 'Limousine' Kentucky bluegrass

² 'Pinnacle' perennial ryegrass

Table 8b. Surface hardness measurements for the grass species study on four different dates in 1998 using a .5 kg hammer. The a and b parts of the individual plots were combined as an overall plot and surface hardness was performed.

Treatments	July 24	August 25	September 29	October 29
1. Kentucky bluegrass1	110.5	107.4	92.3	104.9
2. Kentucky bluegrass	109.3	101.8	82.0	106.7
3. Perennial ryegrass2	115.1	115.7	95.3	120.5
4. Perennial ryegrass	116.5	112.8	95.4	109.1
5. KB1 + PR2	112.7	116.7	92.7	112.9
6. KB + PR	114.4	113.8	96.3	120.7

¹ 'Limousine' Kentucky bluegrass

² 'Pinnacle' perennial ryegrass

Table 8c. Traction measurements(N× m) for the grass species study on four different dates in 1998. The a and b parts of the individual plots were combined as an overall plot and surface hardness was performed. Traction is the average of three measurements.

Treatments	July 24	August 25	September 29	October 29
1. Kentucky bluegrass1	70.7	61.0	68.3	58.5
2. Kentucky bluegrass	75.7	63.0	60.7	65.5
3. Perennial ryegrass2	64.7	56.3	55.8	51.0
4. Perennial ryegrass	65.7	56.8	52.0	47.2
5. KB1 + PR2	58.8	54.2	52.7	53.0
6. KB + PR	60.2	55.3	53.3	51.2

¹ 'Limousine' Kentucky bluegrass

² 'Pinnacle' perennial ryegrass

Table 9. Percent soil moisture (by weight) taken for mat management and grass species study on four different dates.

	7/24/98	8/25/98	9/29/98	10/29/98
Mat Management	4.68	6.98	6.47	8.35
Grass Species	5.91	7.51	8.14	9.81

Table 10a. Ratings of turf quality, color, and % cover for the mat management study on 16 October 1998.

Treatments	Turf Quality (9 = best)	Turf Color (9 = best)	% Turf Cover
1. Catch clippings	6.3	6.3	97.0
2. Return clippings	6.3	6.3	97.7
3. Verticut (prevent thatch)	6.7	7.0	99.0
4. Solid tine aerify	6.3	6.7	99.0
5. PGR (Primo)	8.0	8.0	99.0
6. Verticut (after thatch accumulates)	6.7	6.3	99.0
7. Control seeded	5.3	6.0	86.7
8. Control sodded	5.0	6.0	82.5

Table 10b. Ratings of turf quality and % cover for the grass species study on 16 October 1998.

Treatments	Turf Quality (9 = best)	% Turf Cover
1. Kentucky bluegrass1	7.0	97.7
2. Kentucky bluegrass	7.0	97.7
3. Perennial ryegrass2	4.0	60.0
4. Perennial ryegrass	4.0	61.7
5. KB1 + PR2	4.0	65.0
6. KB + PR	4.0	65.0

¹ 'Limousine' Kentucky bluegrass

² 'Pinnacle' perennial ryegrass

ISU Horticulture:Publications:1999 Turfgrass Report

College of Agriculture