Pre-harvest Core Cultivation of Sod Provides an Alternative Cultivation Timing

Alexander R. Kowalewski, John N. Rogers III, and Timothy D. VanLoo, Department of Crop and Soil Sciences, Michigan State University, East Lansing 48824

Corresponding author: Alexander R. Kowalewski. kowalew8@msu.edu

Abstract

When sand-based athletic fields are renovated with sod, soil textural discontinuity between the sod and the underlying soil is often an issue. Core cultivation can address this issue, but when immediate use of the playing surface is required this practice is often delayed. One possible solution is pre-harvest core cultivation of the sod. Objectives of this study were to determine if pre-harvest core cultivation of Poa pratensis L. sod would decrease strength and weight of sod at harvest, and secondly, if pre-harvest core cultivation can be performed without being detrimental to sod establishment. Pre-harvest and post-establishment core cultivation treatments, both conducted to affect 6% and 12% surface area, plus non-cultivated controls were imposed on sod harvested with conventional (small rolls) and big roll methods at three sites. Pre-harvest core cultivation reduced sod weight up to 18% and strength up to 48% at harvest. Stability of the turf at 40 to 48 days after installation (DAI) was reduced with all core cultivation treatments, regardless of timing based on shear vane strength. However no differences in stability were measured at 72 DAI. Rooting strength and turf shear test strength of pre-harvest core treatments were not affected after 40 and 48 DAI respectively.

Renovating Sand-based Athletic Fields

During the renovation process of sand-based athletic fields, timing is often critical, therefore sod is often the choice for turfgrass establishment. Kentucky bluegrass (Poa pratensis L.) is typically selected for field renovations in the northern regions of the United States because it is a very successful cool season, sports field turfgrass, and its rhizomatous growth habit helps maintain structural integrity during the sod harvesting process (9). Sod, however, is often grown on native soils with fine particle size, resulting in pore size discontinuity when the sod is used to renovate sand-based athletic fields. This discontinuity often compromises rooting because of restricted drainage (7). Soils high in fines (silt and clay) are also susceptible to compaction, which will further decrease water infiltration. Repeated core cultivation, in combination with sand topdressing, can be used to alleviate discontinuous soil layers, restricted drainage, and soil compaction (2,4). This practice, however, is often delayed until after the sports season is completed to prevent surface disruptions during athletic competition. Delaying core cultivation and sand topdressing increases the possibility of turfgrass failure as a result of the prolonged presence of discontinuous pore sizes between the soil types. One possible alternative is pre-harvest core cultivation, allowing field managers to immediately address discontinuous pore sizes at the time of installation. Traditional core cultivation performed after the sod has established, and before athletic competition begins, results in surface disruption during athletic competition. The objectives of this study were to determine if pre-harvest core cultivation of Kentucky bluegrass sod grown on sandy loam soil would decrease overall strength and weight of sod at harvest, and secondly, if pre-harvest core cultivation can be performed without being detrimental to sod establishment and reducing the safety of the playing surfaces.

Timing of Core Cultivation and Sand Topdressing

This experiment was conducted 8 June to 2 September 2004 at two locations. The first location was at the Hancock Turfgrass Research Center (HTRC) in East Lansing, MI on manufactured sand (Plot 1) (Table 1). Site preparation included removal of the existing turfgrass, and roto-tilling the soil to promote sod establishment (1). The second study was conducted at the Michigan State University (MSU) softball field in East Lansing, MI on native loamy sand soil (Plot 2).

Table 1. Soil particle size distribution of experimental plots and sod fields in which sod was grown: Plot 1, Hancock Turfgrass Research Center (HTRC); Plot 2, Michigan State University softball field; Sod Field 1, source of sod (HTRC 2004); and Sod Field 2, source of sod (HTRC 2005), East Lansing, MI, 2004 and 2005.

Particle size (mm)	2004			2005
	Plot 1	Plot 2	Sod field 1	Plot 1	Sod field 2
	Distribution (%)
>2mm	1.3	1.8	2.7	0.0	0.0
Very coarse sand (1.0-2.0)	8.3	1.9	2.2	7.0	2.4
Coarse sand (0.5-1.0)	30.7	3.0	4.1	25.0	5.1
Medium sand (0.25-0.5)	45.6	14.9	11.5	49.2	15.1
Fine sand (0.1-0.25)	11.2	36.6	28.5	14.9	28.4
Very fine sand (0.05-0.1)	0.9	17.5	13.5	0.6	13.5
Silt (0.05-0.002)	0.9	14.5	23.3	1.1	22.4
Clay (<0.002)	1.1	9.8	14.2	2.2	13.1
Soil type	Sand	Loamy sand	Sandy loam*	Sand	Sandy loam*

* Aubbeenaubbee-Capac sandy loam.

Pre-harvest core cultivation was performed 8 June 2004 on Kentucky bluegrass (25% Showcase, 25% SR 2284, 25% Coventry, and 25% America) sod (Sod Field 1), seeded eleven months prior, grown on native Michigan soil (Aubbeenaubbee-Capac sandy loam). A Toro Procore 660 with Titan 19 mm (diameter) side-eject tines (62-mm side spacing, and 76-mm forward spacing) (Toro, Bloomington, MN), at 6% and 12% affected surface area , one and two passes, respectively, was used for core cultivation. Core cultivator starting position was staggered to prevent tines from penetrating the same surface area. Big roll (0.5 × 3.1 m), and conventional (0.6 × 1.4 m), sod was harvested 12 June 2004 at 19-mm depth then laid on the appropriate plots (3.1 m long × 1.8 m wide) (Fig. 1). Big roll sod was harvested with a WMI Rollmaster (WMI Inc., Elberta, AL), while conventional sod was harvested with a Brouwer (Brouwer Turf Equipment, Dalton, OH) conventional sod harvester. The big roll harvester wrapped the sod in a plastic net during harvest, which was removed at the time of sod installation. Starter fertilizer (16-25-13) (Lebanon Turf Products, Lebanon, PA) was applied at 48.8 kg of P per ha to the research plots prior to sod application. Sand (3.2 mm) was topdressed into the pre-harvest core cultivation treatments after the sod was laid. Post-establishment core cultivation and topdressing were applied 2 July 2004. Core cultivation treatments at this time include pre-harvest core cultivation at 6 and 12% affected surface area, performed 8 June 2004, post-establishment core cultivation at 6 and 12% affected surface area and a control. Poly coated fertilizer (26-7-14) (Agrium, Sylacauga, AL) was applied once at 48.8 kg of N per ha three weeks after installation.

Fig. 1. Kentucky bluegrass sod established on an Aubbeenaubbee-Capac sandy loam placed on sand at the HTRC, East Lansing, MI, 2004. Big roll sod (0.5 × 3.1 m) harvested with a WMI Rollmaster (WMI Inc., Elberta, AL), with control cultivation treatment (left) and conventional sod (0.6 × 1.4 m) harvested with a Brower conventional sod harvester, with core cultivation 6% affected surface area (right).

In 2005, plot 1 was renovated with the same procedures as in 2004. On 17 June 2005 pre-harvest core cultivation was performed. Sod, seeded nine months prior with the same Kentucky bluegrass varieties, was harvested from a different location within the HTRC (Sod Field 2), laid and topdressed following the procedures used in 2004. Post-establishment core cultivation and topdressing was applied 12 July 2005. Research concluded 5 September 2005. Experimentation at the MSU softball field was not repeated because in 2004 the experiment coincided with field renovation with sod. In 2005, the softball field was actively being used and repeating the experiment at this location was not an option.

Kentucky Bluegrass Sod Evaluation

Sod weight and strength as well as soil moisture at the time of harvest were determined the day sod was harvested. Weight (kg/m²) was obtained at the time of harvest using an electronic scale, 1.0 g readability (Sartorius Corp., Bohemia, NY). Sod strength was obtained with a Calrochan sod-puller (manufactured by R. N. Calhoun and J. C. Sorochan, MSU, East Lansing, MI), which horizontally pulls sod apart and measures the strength (kg) necessary to tear 0.09-m² sod samples (6). Sod soil moisture (v/v) was determined after harvest with a Trime-FM Mobile moisture meter, 5.1-cm probe (MESA Systems Co., Medfield, MA) inserted horizontally into the soil. Soil moisture data was used to derive the dry soil weights to prevent localized wet and dry spots from compromising soil weights.

Establishment and stability data measured by the Eijkelkamp shear vane and Clegg turf shear tester, and turfgrass quality were collected weekly starting after post-establishment core cultivation treatments were performed 24 days after installation (DAI) until the conclusion of the experiment (48 DAI). Follow-up data was collected 72 DAI.

Turfgrass shear strength was evaluated using the Eijkelkamp shear vane (Eijkelkamp, Giesbeek, the Netherlands) and Clegg turf shear tester (TST) (Baden Clegg PTY Ltd., Wembley DC, WA, Australia). Shear vane data were collected to measure the torque (shear resistance) in Newton meters (Nm) of the turfgrass. TST data were collected to measure the divot resistance or force (Nm) required to horizontally displace the turfgrass surface, using a 50 mm (wide) × 40 mm (insertion depth) paddle (5).

Visual quality ratings were based on the National Turfgrass Evaluation Program (NTEP) system of rating, a 1 to 9 scale, with 1 = dead, 6 or greater = acceptable, and 9 = ideal turfgrass (3).

Rooting strength (kg) was evaluated using sod boxes [PVC ring (170 mm diameter, 51 mm depth) with a nylon screen] installed in the sand under the 19 mm thick sod layer. Boxes, three subsamples per replication aligned in rows to accommodate mowing, were installed at experiment initiation then pulled 48 DAI using a hydraulic sod-puller and recorded using a loading cell (1).

Sod weight, strength and soil moisture data were analyzed as a 2 × 3 × 2 factorial, randomized complete block design with three replications using Agricultural Research Management (ARM, Gylling Data Management Inc., Brookings, SD). The three studied factors were sod source (Sod Field 1 and Sod Field 2), core cultivation (pre-harvest core cultivation 6% affected surface area, pre-harvest core cultivation 12% affected surface area, and control) and sod harvesting method [big roll sod (0.5 × 3.1 m), and conventional (0.6 × 1.4 m)].

Shear vane, TST and visual quality, data were analyzed as a 3 × 5 × 2 factorial, with the same experimental design as above with the addition of the MSU softball field (Plot 2: Sod Field 1) and post-establishment core cultivation at the 6% and 12% affected surface area. Mean separations were analyzed using Fisher’s protected least significant difference (LSD) at a 0.05 level of probability.

Rooting strength were analyzed as a 2 × 5 × 2 factorial, randomized complete block design with three replications. Factors were sod source (Plot 1: Sod Field 1 and Plot 1: Sod Field 2), core cultivation (pre-harvest core cultivation at 6 and 12% affected surface area, post-establishment core cultivation at 6 and 12% affected surface area, and control) and sod harvesting method (big roll sod, and conventional). Plot 2: Sod Field 1 was excluded due to the fact that sod boxes would disrupt athletic field use.

Pre-harvest Core Cultivation Decreased Overall Strength and Weight at the Time of Harvest

Regarding sod weight, moisture content and strength at the time of harvest, main effects were significant except for the effects of sod source on strength and core cultivation method on moisture content. The only interactions observed were the effects of core cultivation × sod harvesting method on sod strength.

Sod Field 2 soil moisture content was substantially higher than Sod Field 1, up to 85% higher at the time of harvest, likely the result of irrigation practices (Table 2). Big roll sod soil moisture content was greater than conventional sod.

Table 2. Effects of core cultivation and sod harvesting method on Kentucky bluegrass sod* weight, moisture content and strength at the time of sod harvest, Hancock Turfgrass Research Center.

		Weight (moist) (kg/m²)	Moisture (v/v)	Weight (dry) (kg/m²)	Strength (kg 0.09/m²)
Sod source	Sod Field 1	13.9 b	4.1 b	13.3 b	67.4
	Sod Field 2	18.7 a	19.3 a	15.1 a	63.5
	LSD_(0.05)	1.2	2.1	1.2	NS
Core cultivation	Pre-harvest 6.0% affected surface area	16.4 b	12.2	14.2 b	64.2 b
	Pre-harvest 12.0% affected surface area	14.7 c	11.6	12.8 c	45.1 c
	Control	17.9 a	11.3	15.6 a	87.1 a
	LSD_(0.05)	1.5	NS	1.5	5.5
Sod harvesting method	Conventional	15.1 b	10.6 b	13.4 b	59.6 b
	Big Roll	17.5 a	12.8 a	15.1 a	71.3 a
	LSD_(0.05)	1.2	2.1	1.2	4.5

* Sod established on an Aubbeenaubbee-Capac sandy loam. Lower case letters represent significant differences at a 0.05 level of probability. NS = no significance.

Pre-harvest core cultivation 12% affected surface area had the greatest reduction in sod weight, up to 18%, and strength up to 48%, at the time of harvest (Table 2). The control, in comparison to the pre-harvest core cultivation treatments, had the greatest sod weight and strength, suggesting that if initial strength is a priority the control will provide the best results. Big roll sod was 14% heavier and 16% stronger than conventional sod.

Core cultivation and sod harvesting method interactions were also observed (Fig. 2). Big roll sod was greater in strength than conventional sod at the pre-harvest core cultivation 6% affected surface area and control rate. This interaction suggest that the big roll harvesting method will provide a stronger sod when core cultivated at the pre-harvest 6% affected surface area and the control rate.

Fig. 2. Effects of pre-harvest core cultivation x sod harvesting method on Kentucky bluegrass sod strength (kg 0.09/m²) at the time of sod harvest, Hancock Turfgrass Research Center. Sod established on an Aubbeenaubbee-Capac sandy loam. Lower case letters represent significant differences at a 0.05 level of probability.

Pre-harvest Core Cultivation was not Detrimental to Kentucky Bluegrass Sod Establishment

All main effects produced significant shear vane results. Interactions between sod source × core cultivation and core cultivation × sod harvesting method were observed on one occasion only without biological significance.

Plot 1: Sod Field 1 produced the lowest shear vane results 72 DAI only (Table 3). Thirty DAI pre-harvest core cultivation at 6 and 12% affected surface area produced the lowest shear vane values, in comparison to the other core cultivation treatments. On 40 and 48 DAI all core cultivation treatments were less than the control, regardless of timing or affected surface area, supporting earlier statements that if initial stability is a priority, the control will provide the strongest sod. Seventy-two DAI, no differences were observed between core cultivation treatments. Results suggest that pre-harvest core cultivation will initially reduce sod shear vane strength (30 DAI), but will be no different than post-establishment core cultivation 40 DAI and the control 72 DAI, suggesting that if adequate time (72 DAI) is provided for establishment prior to athletic use core cultivation regardless of timing or rate will provide shear vane strength comparable to the control. Differences between sod harvesting methods were observed 30, 40 and 72 DAI, with big roll sod resulting in the higher shear vane values.

Table 3. Effects of experimental site, core cultivation and sod harvesting method on Eijkelkamp shear vane ratings of Kentucky bluegrass sod.*

		Days after installation
		30	40	48	72
		Eijkelkamp shear vane rating (Nm)
Experi- mental Site	Plot 1: Sod Field 1	23.1	24.5	22.7	23.6 b
	Plot 2: Sod Field 1	23.9	24.5	22.5	25.0 a
	Plot 1: Sod Field 2	23.4	25.4	22.1	25.2 a
	LSD_(0.05)	NS	NS	NS	1.0
Core cultivation	Pre-harvest 6.0% affected surface area	23.0 bc	24.6 b	21.8 b	24.1
	Pre-harvest 12.0% affected surface area	22.0 c	23.6 b	22.2 b	24.6
	Post-establishment 6.0% affected surface area	23.8 ab	24.1 b	21.9 b	24.9
	Post-establishment 12.0% affected surface area	23.2 b	24.7 b	22.2 b	24.1
	Control	25.3 a	27.1 a	24.0 a	25.3
	LSD_(0.05)	1.7	1.9	1.5	NS
Sod harvesting method	Conventional	22.6 b	23.9 b	22.3	24.0 b
	Big Roll	24.3 a	25.7 a	22.6	25.2 a
	LSD_(0.05)	1.1	1.2	NS	0.9

* Sod established on an Aubbeenaubbee-Capac sandy loam. Lower case letters represent significant differences at a 0.05 level of probability. Nm = Newton meters; NS = not significant.

With respect to TST results, core cultivation and sod harvesting method main effects were observed 30 DAI only. Sod source × sod harvesting method and core cultivation × sod harvesting method interactions were also observed. However, sod source × sod harvesting method interactions were not biologically significant.

Pre-harvest core cultivation 12% affected surface area and post-establishment 6% affected surface area were less than the control on this date only (Table 4). Results suggest that pre-harvest and post-establishment core cultivation will initially reduce TST strength; however if adequate time is allowed for establishment (40 DAI) TST strength will be no different than the control. Big roll sod resulted in higher TST values on this date as well. An interaction was also observed on this date only between core cultivation and sod harvesting method, both the control and pre-harvest core cultivation 6% affected surface area had greater TST values when harvested with the big roll sod method (Fig. 3). No turfgrass quality differences, main effect or interactions, were observed throughout the data collection period.

Table 4. Effects of experimental site, core cultivation and sod harvesting method on Clegg turf shear tester ratings (Nm) of Kentucky bluegrass sod.*

Experimental site	Days after installation
	30	40	48	72
	Turf shear ratings (Nm)
Plot 1: Sod Field 1	72.0	93.2	101.8	112.6
Plot 2: Sod Filed 1	71.4	88.8	100.0	109.7
Plot 1: Sod Field 2	70.8	91.9	101.6	115.7
LSD_(0.05)	NS	NS	NS	NS
Core cultivation
Pre-harvest 6.0% affected surface area	72.0 ab	90.7	99.8	110.5
Pre-harvest 12.0% affected surface area	64.4 c	89.8	97.5	117.4
Post-establishment 6.0% affected surface area	68.7 bc	90.3	101.0	113.4
Post-establishment 12.0% affected surface area	75.3 a	90.9	103.5	109.7
Control	76.8 a	94.4	103.9	112.0
LSD_(0.05)	6.2	NS	NS	NS
Sod harvesting method
Conventional	68.3 b	89.6	98.7	113.0
Big Roll	74.5 a	92.7	103.7	112.2
LSD_(0.05)	3.9	NS	NS	NS

* Sod established on an Aubbeenaubbee-Capac sandy loam. Lower case letters represent significant differences at a 0.05 level of probability. Nm = Newton meters; NS = not significant.

Fig. 3. Effects of core cultivation x sod harvesting method on Clegg turf shear tester strength (Nm) of Kentucky bluegrass sod, 30 days after installation. Sod established on an Aubbeenaubbee-Capac sandy loam. Lower case letters represent significant differences at a 0.05 level of probability.

Sod source and sod harvesting method main effects produced rooting strength differences, while no interactions were observed.

Core cultivation, regardless of timing or affected surface area, produced no differences in rooting strength (Table 5). Differences in sod harvesting methods were observed with the big roll sod providing stronger rooting than conventional sod.

Table 5. Effects of experimental site, core cultivation, and sod harvesting method on rooting strength (kg) of Kentucky bluegrass sod, 48 days after installation.

Experimental site	Days after installation
	48
	Rooting strength (kg)
Plot 1: Sod Field 1	11.1 b
Plot 1: Sod Field 2	12.9 a
LSD_(0.05)	0.9
Core cultivation
Pre-harvest 6.0% affected surface area	11.9
Pre-harvest 12.0% affected surface area	12.6
Post-establishment 6.0% affected surface area	12.3
Post-establishment 12.0% affected surface area	12.2
Control	11.1
LSD_(0.05)	NS
Sod harvesting method
Conventional	11.5 b
Big Roll	12.5 a
LSD_(0.05)	0.9

Sod established on an Aubbeenaubbee-Capac sandy loam. Lower case letters represent significant differences at a 0.05 level of probability. NS = not significant.

Conclusion

Initial differences observed between Sod Field 1 and Sod Field 2 soil moisture content were likely the result of an automatic irrigation system, which was available at Sod Field 2, and applied irrigation daily up until the time of harvest. Sod Field 1 irrigation was applied using a manual system, and was last applied two days prior to sod harvest.

Pre-harvest core cultivation reduced sod weight at the time of harvest, which could potentially reduce shipping weight or increase shipping volume per load. Pre-harvest core cultivation reduced sod strength, without affecting the harvesting or sod installation process, however if heavy field use were to commence immediately following installation this reduction in strength would likely reduce initial stability. Results also suggest that this big roll sod harvester provides a heavier and stronger sod, likely because it was less abrasive to the sod during harvest and wrapped the sod during harvest with a plastic net.

Shear vane values and rooting strength results collected from Plot 1: Sod Field 2 was greater than the other experimental sites, again possibly the result of an automatic irrigation system, which was available at Sod Field 2 only. This system provided daily irrigation, which would have prevented possible drought stress allowing the turfgrass to develop a more extensive rooting system throughout the summer prior to harvest.

Results indicate that pre-harvest core cultivation can be performed with minimal effects to sod strength if adequate time is allowed for establishment. Pre-harvest and post-establishment core cultivation, regardless of timing and rates, had no detrimental effects on shear vane strength 72 DAI, TST strength 40 to 72 DAI, and rooting strength 48 DAI. Therefore, if 72 days or more are available for sod establishment, pre-harvest and post-establishment core cultivation at the 6 or 12% affected surface area can be performed to begin addressing discontinuous soil pore sizes, and provide sod stability equal to the control. Core cultivation treatments, regardless of timing or rate, decreased shear vane strength 30 to 48 DAI and TST strength 30 DAI suggesting that if early stability, rather than addressing discontinuous soil pore sizes, is a priority the control is the best option.

Big roll sod shear vane, TST and rooting strength results, much like initial sod strength, suggest that this harvesting method provide a consistently stronger sod at the time of harvest and throughout the sod establishment period.

To resolve potential soil layering problems, repeated core cultivation and sand topdressing throughout the year is required (2,4). Findings from this research do not provide a solution to those facing this dilemma, rather an extra core cultivation timing, which does not substantially affect the sod harvest, installation or strength in comparison to traditional post-establishment core cultivation.

Literature Cited

1. Lee, D. K., and Rieke, P. E. 1993. Soil cultivation effects on establishment of Poa pratensis L. sod. Intnl. Turfgrass Soc. Res. J. 7:437-443.

2. McCarty, L. B., Gregg, M. F., and Toler, J. E. 2007. Thatch and mat management in an established creeping bentgrass golf green. Agron J. 99:1530-1537.

3. Morris, K. N. 2008. A guide to NTEP turfgrass ratings. Online. National Turfgrass Evaluation Program (NTEP), Beltsville, MD.

4. Murphy, J. A., Rieke, P. E., and Erickson, A. E. 1993. Core cultivation of a putting green with hollow and solid tines. Agron. J. 85:1-9.

5. Sherratt, P. J., Street, J. R., and Gardner, D. S. 2005. Effects of biomass accumulation on the playing quality of a Kentucky bluegrass stabilizer system used for sports fields. Agron. J. 97:1107-1114.

6. Sorochan, J. C., and Rogers, J. N. III. 1999. Measuring sod strength of Kentucky bluegrass and supina bluegrass. TurfGrass Trends 8:6-9.

7. Spomer, L. A., and Turgeon, A. J. 1977 Vertical soil water retention in newly-sodded, drained turfgrass sites. Comm. Soil Sci. Plant Analysis. 8:417-423.

8. Stier, J. C., Rogers, J. N. III., Crum, J. R., and Rieke, P. E. 1999. Flurprimidol effects on Kentucky bluegrass under reduced irradiance. Crop Sci. 39:1423-1430.

9. Turgeon, A. J. 2005. Turfgrass Management, 7th Edn. Pearson Ed., Upper Saddle River, NJ.