Comparisons of root-zone amendments allow researchers to evaluate which ones provide the fastest grow-in of creeping bentgrass under putting green conditions.

Creeping bentgrass seeded on peat-amended sand established more quickly than seedings on other media. Sand-only root zones often have low fertility because of leaching and poor cation exchange capacity. Greens construction is expensive, so proper choices of root-zone amendments are important to delay expensive reconstruction.

Golfers prefer consistent, playable putting surfaces regardless of the agronomic practices required to maintain them. Moreover, putting greens are rarely closed to allow recovery for any reason. They are subjected to daily mowing, watering and unending traffic. If their root zones are not properly built, greens become compacted, turfgrass declines, and playing conditions deteriorate.

Desirable characteristics for a putting green media include adequate infiltration of water, resistance to compaction, adequate aeration, proper water-holding capacity and nutrient retention. These characteristics must also provide a surface that is receptive to golf shots. Such a putting surface is expensive to build, so the green and its individual components should be durable to delay reconstruction as long as possible.

Although sand and peat are traditional choices for building putting green root zones, alternative products frequently appear on the market with promises of superior root-zone characteristics. So far, research reveals strong performance by peat-amended sand root zones, although some inorganic amendments at times perform better than pure sand root zones.

USGA recommendations
Many creeping bentgrass (Agrostis palustris) greens are grown on high-sand media that meet USGA standards (3).

The primary sand content in these specifications provides good drainage, compaction resistance and aeration for root growth, but can be inefficient at retaining adequate moisture and nutrients for turfgrass growth (1). Therefore, organic and inorganic amendments are possible tools for maximizing plant-available water and nutrient retention (10).

Peat
Peat, the most common amendment used in putting green construction, provides an organic source in rooting media. Furthermore, peat added to sand reduces the soil's bulk density, improves aeration (5), allows the media to retain more plant-available water (6) and allows for a gradual release of available water (4). During establishment, peat's ability to hold more water at the soil surface also allows for improved germination. Proper irrigation practices are critical, for peat-amended greens may become excessively wet under improper water management (5).

With natural decomposition, peat eventually loses its desirable characteristics (2). By then, the turfgrass itself may replenish the lost organic content by seasonal root sloughing and secretion of organic compounds.

Ceramic clays
Ceramic clay amendments are inorganic materials derived from mined expanding clays, usually montmorillinite or illite. The clay is heated to 500 F to 1,300 F and screened for size distribution. It is common for products needing stability, such as soil amendments, to be heated hotter and longer than other ceramic clay products. By super-heating, the original expanding clay mineral is permanently transformed into a stable, porous particle. Similar to ceramic clays, calcined clays are made from the same clay minerals, but heated at lower temperatures for a shorter duration, reducing production costs.

Desirable soil amendment characteristics of ceramic clays include resistance to degradation, low bulk densities (about 0.56 grams per cubic centimeter), high porosity and greater water-holding capacity than sand (12). These physical properties allow ceramic clays to withstand compaction and improve infiltration and aeration.

A disadvantage to the heating process is the loss of nutrient retention. In their natural forms, these clays have high cation exchange capacities -- approximately 30 milliequivalents of charge per 100 grams of material for illite and 100 milliequivalents for montmorillinite. However, it is suspected that the interlayer exchange sites are compromised by the heating process, therefore reducing the cation exchange capacity to about 9 milliequivalents per 100 grams. However, the nutrient retentive properties are greater than sand, which has a negligible 0.25 milliequivalents per 100 grams (7). Another reported disadvantage of ceramic clays is water being bound too tightly within the clay particle, making it unavailable to the turfgrass plant (12).

Diatomaceous earth
Accumulations of diatom shells (produced by certain algae) from ancient seabeds are mined as diatomaceous earth. Because mined diatomaceous earth contains greater than 85 percent silica, it is considered chemically inert (11). Some commercial diatomaceous earth amendments are similar to ceramic clays in that they are heated (or calcined), whereas some products are merely dried raw material. In either case, diatomaceous earth is porous, stable and has a low bulk density (about 0.39 gram per cubic centimeter) (12).

Diatomaceous earth products have a relatively low cation exchange capacity (about 5.5 milliequivalents of charge per 100 grams of material). However, diatomaceous earth does have high specific surface area (89 to 123 square meters per gram), which contributes to greater nutrient retention than sand (7).

Published reports of field research with diatomaceous earth in turfgrass are sparse. One research team reported Penncross creeping bentgrass plots containing a diatomaceous earth product maintained normal growth for 15 days without watering, whereas ceramic clay-amended plots needed watering after five days (9). To improve water-holding properties, another team recommended the use of diatomaceous earth as an amendment to sand (8). However, another report indicates that water is bound too tightly for plant use and is therefore unavailable in diatomaceous earth (12).

Research objectives
The use of inorganic soil amendments for golf putting green construction has increased over the past few years, but research on short- and long-term field performance of these amendments is deficient. The overall objective of this research was to gain an understanding of golf course putting green construction methods with respect to internally porous amendments.

Materials and methods
A 20,000-square-foot, bentgrass research golf green with USGA-style drainage was established in 1997 on the Walker Course at Clemson University. In one section of the green, plots were established to evaluate inorganic root-zone amendments. Individual cells were 9 feet by 15 feet and randomly replicated three times.

The amendment ratios by volume included:

	100 percent sand
	85 percent sand to 15 percent sphagnum peat
	85 percent sand to 15 percent ceramic clay
	85 percent medium sand to 14 percent diatomaceous earth to 1 percent kelp organic

Plots were seeded Oct. 8, 1997, with L-93 creeping bentgrass at 1.5 pounds per 1,000 square feet. The entire plot area was irrigated multiple times daily to achieve germination. Plots were fertilized, treated with fungicides and insecticides, and irrigated to promote healthy turfgrass.

Mowing was performed daily by the Walker Course maintenance staff at the same height (less than ¹/8 inch) as greens on the golf course.

Turf density and color
Monthly evaluations were made for turfgrass density and color. Density was rated as a visual percentage of the plot covered with turfgrass. Turfgrass color was rated on a scale of 1 to 9, where 1 indicated brown, dead turf; 7 indicated minimally acceptable green color; and 9 indicated green, healthy turf.

Turfgrass establishment and color
Plots containing peat established more quickly than the straight sand or the mixes containing an inorganic soil amendment. Six months after seeding, grass in the rooting media with peat had 95 percent coverage, whereas plots with inorganic amendments did not exceed 95 percent cover until nine months after seeding. At 18 months after seeding, plots with 100 percent medium sand achieved 90 percent coverage. After 2.5 years, all plots had established to acceptable (90 percent or greater) coverage.

The summer of 1999 was very hot and dry. In Clemson, S.C., during July and August, 33 consecutive days sweltered with daytime highs of 90 F or hotter, and nighttime lows were 70 F or greater 45 percent of the time.

As a result, turfgrass thinned in all plots. Only the diatomaceous earth-amended plots had more than 90 percent cover, while plots containing 100 percent sand, peat and ceramic clay had 80 percent to 89 percent cover. Plots with peat reestablished to more than 90 percent cover within three months.

Turfgrass color comparisons were not possible until ample cover for all treatments had occurred, which was nine months after seeding. All plots were equally fertilized through the first two years of this study.

In general, turfgrass color was acceptable (rated at 7.0 or greater) in all amendments for the first 24 months following seeding. The 27-month rating was taken after two weeks of cold weather (two consecutive weekends of snow and freezing rain with night temperatures below freezing and daytime temperatures not exceeding 40 F). The plots with peat and diatomaceous earth as amendments retained acceptable color.

Conclusion
These data indicate that peat-amended sand allowed bentgrass to establish three months sooner than sand plots amended with either ceramic clay or diatomaceous earth. It is likely that the peat retained more water at the soil surface, keeping the seed moist and allowing for improved germination. However, nine months after seeding, all amended plots had adequate turfgrass coverage. Once established and actively growing, turfgrass in all amended plots had acceptable color, which was better than the color in plots with 100 percent sand.

The greatest strengths of the inorganic amendments are their resistance to degradation and breakdown. Now that turf is established, further performance evaluations of inorganic amendments will be made regarding their durability.

Acknowledgments

For contributions of material and labor, we thank Simmons Irrigation, Golf Agronomics, Southern Soil Technologies, Profile Products LLC and PSA. For assistance in construction and maintenance, we acknowledge the staff at The Walker Course at Clemson University and the numerous student laborers. We extend special thanks to Jason Higingbottom and Todd Bunnell.

Literature cited

1. Beard, J.B. 1973. Turfgrass science and culture. Prentice Hall, Englewood Cliffs, N.J.
2. Huang, Z.T., and A.M. Petrovic. 1995. Physical properties of sand as affected by clinoptilolite zeolite particle size and quantity. Journal of Turfgrass Management 1(1):1-15.
3. Hummel, N.W., Jr. 1993. Rationale for the revisions of the USGA green construction specifications. USGA Green Section Record 31(2):7-21.
4. Juncker, P.H., and J.J. Madison. 1967. Soil moisture characteristics of sand-peat mixes. Soil Science Society of America Proceedings 31:5-8.
5. Letey, J., W.C. Morgan, S.J. Richards and N. Valoras. 1966. Physical soil amendments, soil compaction, irrigation, and wetting agents in turfgrass management III. Effects on oxygen diffusion rate and root growth. Agronomy Journal 58:531-535.
6. McCoy, E.L. 1992. Quantitative physical assessment of organic materials used in sports turf rootzone mixes. Agronomy Journal 84:375-381.
7. McCoy, E.L., and R.C. Stehouwer. 1998. Water and nutrient retention properties of internally porous inorganic amendments in high sand content root zones. Journal of Turfgrass Management 2(4):49-69.
8. Oppold, R.S., and staff. 1997. ISTRC's guidebook to your greens. International Sports Turf Research Center, Inc.
9. Ralston, D.S. and W.H. Daniel. 1973. Effects of porous rootzone materials underlined with plastic on the growth of creeping bentgrass (Agrostis palustris Huds). Agronomy Journal 65:229-232.
10. Sartain, J.B. 1995. Effects of clay and polymer amendments on the physical and chemical properties of soil. Journal of Turfgrass Management 1(2):1-18.
11. Sylvia, D.M., J.J. Fuhrmann, P.G. Hartel and D.A. Zuberer. 1999. Principles and applications of soil microbiology. Prentice Hall, Upper Saddle River, N.J.
12. Waddington, D.V. 1992. Soils, soil mixtures, and soil amendments. p. 331-383. In: D.V. Waddington, R.N. Carrow and R.C. Shearman (eds.), Agronomy Monograph No. 32. Turfgrass. American Society of Agronomy, Madison, Wis.

Clint Waltz is a graduate assistant, and Bert McCarty, Ph.D., is a turfgrass professor at Clemson University in South Carolina.