Regardless of the kinds of amendments and the relative proportions of perlite that are tried, a poor quality of sand is difficult to overcome. In particular, while the perlite amended mixtures with coarse and fine sands meet some of the USGA specifications, they do not meet them all.
Infiltration rate is the biggest problem for these two sands, and perlite additions could overcome neither the low infiltration rate of fine sand nor the extremely high infiltration rate of coarse sand. Although the addition of perlite did improve these mixtures, it did not negate the influence of sand particle size.
The problems with both fine and coarse sands are inherent and are the basic reason medium sands are recommended for green construction. The discussion that follows, therefore, emphasizes the results and implications of adding various percentages of perlite to golf green mixtures composed of medium sands,
Soil compaction is probably the most serious problem on intensively used turf areas such as golf greens. The addition of perlite to the green mixtures generally decreased bulk density for the treatments evaluated. Although little effect on bulk density was noted for the medium sand treatments with 10 percent perlite, a 20 percent perlite addition decreased the bulk density from 1.62 g/cm3 to 1.42 g/cm3, a level which falls in the middle of the range that the USGA recommends to reduce problems associated with compaction.
Both the water retention and infiltration rates for greens mixtures are important to the overall management of golf greens; the ideal soil mixture should retain enough water to meet turf needs but at the same time be sufficiently aerated to allow excess water to drain quickly. With the total porosity around 35-40 percent for all three medium sands, regardless of clay content, the addition of 20 percent perlite by volume yielded the greatest total porosity among the medium sand samples; the greatest noncapillary porosity among the medium sands also occurred in the 20 percent perlite mixture.
It should be noted again that while perlite amendments improved the infiltration rates for both the fine and the coarse sands, in neither case was the improvement sufficient for the mixtures to meet the USGA specifications. In fact, the high silt content in the fine sands caused the infiltration rate to remain very low, even with the addition of 40 percent perlite.
Used with medium sands, however, perlite amendments decreased the infiltration rate to within the recommended range of 50 to 250 mm per hour regardless of clay con tent; the medium sands with 20 percent perlite also had acceptable water retention values. These observations indicate that the soil will retain enough water to promote a healthy turf while controlling the potential for problems with water logged soil.
By contrast, medium sands without perlite were at or below the 12 percent USGA recommendation for water retention. Thus, perlite raised this value to between 12 and 16.5 percent – depending on clay content – and, in general, water retention increased in proportion to increased clay content in medium sand treatments.
Because of the variations in particle size distribution and shape, even among sands classed as medium, any specific sand proposed for golf green mixtures must be tested with amendments before a mixture can be recommended reliably. Although the addition of perlite on a 20 percent by volume basis provided some benefit to all treatments evaluated, these benefits proved adequate only when the mixture was prepared using the medium sand selected for the study. Of the three sands tested, only the medium sand with 1.5 percent and 3.0 percent clay and the coarse sand with 1.5 percent clay met the USGA recommendations for silt and clay contents.
The medium sands with clay contents ranging from 1.5 to 4.5 percent and 20 percent perlite by volume met all of the recommended USGA physical measurements for greens mixtures. Unlike those prepared with medium sands, none of the treatments prepared with fine or coarse sands could meet all of these standards.
The results of this laboratory study demonstrate that perlite amendments benefit the physical characteristics of soils that are important to green performance. Another advantage of perlite is that – unlike organic matter amendments which gradually decompose perlite is inert in the soil mixture and therefore does not change significantly over time. Finally, because it is a manufactured product, perlite is of consistent quality and does not vary as organic amendments do.
Case Study:
Given the positive results of laboratory testing, a question that remains is, “How does a perlite-amended green perform in the field, especially over the long term?” The answer to this question should be evident from the following case study of perlite-amended greens that have been in use for several years.
In 1974, the Los Angeles Department of Recreation and Parks (LADRP) began using perlite as an amendment in the construction of public golf courses. To date, perlite has been used at these locations: Encino, Griffith, Hansen Dam and Woodley. The top mix for the greens consisted of 70 per cent plaster sand, 20 percent horticultural perlite of fine sand size and 10 percent nitro humus.
At Woodley, the first set of eleven greens to receive this perlite-amended mixture in place of the original native soil material has supported a healthy turf and excellent play for more than 10 years. Because of this initial success, other greens that needed renovation were rebuilt with greens mixtures composed of sand, perlite and organic matter.
Penn cross bent grass and improved varieties of Bermuda-grass are being grown on these unique greens. In fact, the greens have remained in good physical condition after as many as 100,000 rounds of play each year at the course, according to assistant manager Steve Ball of Encino.
In addition, golfers may resume play with only a short delay after a fairly heavy rain, as witnessed by the authors when an intense storm occurred during a site inspection at the Encino course. During this inspection and during visits to the other three courses, samples of sand and perlite amended greens were collected so that their physical conditions could be compared to the USGA specifications.
The results of the laboratory and field-testing are presented in Table 2, which includes the green number and its approximate age. A comparison of these data (Table 2) with the USGA specifications (Table 1) provides a good explanation of why the greens have performed so well.
