A study was initiated in November 1997 at an Ames High School football practice field in Ames, Iowa, to evaluate calcined clay (Turface^® MVP) in a tilled renovation procedure. The soil contained 54% sand, 7% silt, and 39% clay. The 15,750 sq. ft. experimental plot area was arranged between the hash marks and the goal lines. Each individual plot measured 15 ft. by 50 ft. and was centered on every yard line marker (goal line, 5, 10, 15, 20, etc.) (Table 1) such that 7.5 ft. was on one side of the yard line and 7.5 ft. was on the other side of the same yard line. Treatments consisted of calcined clay at 1 ton/1000 sq. ft., calcined clay at 2 tons/1000 sq. ft., and an untreated control (Table 2). Treatments were randomized in each block and replicated seven times. Each replication was 45 ft. by 50 ft. with three treatments. Treatments were topdressed at their respective rate and tilled into the top 4 inches of soil with a Rotadairon (Bryan Wood, Commercial Turf & Tractor). Each large plot was individually dragged with a steel mat to prepare the surface for seeding and prevent cross contamination of treatments. The study area was initially seeded in May 1998 at 3 lb/1000 sq. ft. with a bluegrass blend containing equal parts of ‘Nublue’, ‘Limousine’, and ‘Touchdown’. The field was primarily used for autumn football practice (September through November) and spring soccer (April and May). As a routine maintenance practice, the field was hollow cored on 3-inch centers with 0.75-inch hollow tines each year in late November. The test area was drill seeded with perennial ryegrass at 10 lbs/1000 sq. ft. on 9 June 1999 and 5 June 2000. Each year the plot area located between the hash marks on the field began with a minimum of 90 percent turf cover in September and by May the following year there was exposed soil with less than 50 percent turf cover.

Three undisturbed soil columns measuring 5.2 cm in diameter and 6.1 cm in length were collected from the top 6.5 cm of each treatment for four blocks in November 1999 and September 2000. Saturated hydraulic conductivity (K_sat) at 34 cm constant water head and soil bulk density were determined for undisturbed field samples (Klute and Dirksen, 1986). The K_sat data were converted to values at 20°C before statistical analysis.

Means were separated using Fisher’s least significant difference (LSD) in the analysis of variance (ANOVA) procedure in the Statistical Analysis System (SAS version 6.12, SAS Institute, 1996).

Bulk density represents the weight of soil per unit volume and thus provides a direct measurement of soil compaction. Intense traffic from sport activities causes soils to be compressed near the surface resulting in the displacement of soil pores by soil solids. Higher BD represents less pore space, less favorable growing conditions, and harder playing surfaces. On 7 Nov 1999, after one year of traffic, there were no significant differences among treatments. By the end of the second year of field use, the soil amended with 1 or 2 tons/1000 sq. ft. of Turface resulted in a significant BD reduction. On 26 Sept 2000 the BD for the 1 or 2 ton/1000 sq. ft. rate of Turface was below 1.37 g cm^-3 compared to the control that was at 1.53 g cm^-3. This indicates that soils amended with Turface maintain a more favorable BD for plant growth. This reduction in BD could reduce surface hardness and improve penetration by cleated shoes and tined aerifier equipment.

The K_sat is a measurement of how fast water flows through a soil profile under saturated conditions. Higher K_sat values indicated that excessive water will drain through the soil profile faster. In both years there was no difference in water movement between the control and the 1 ton/1000 sq. ft. rate of Turface, however, the 2 ton/1000 sq. ft. rate of Turface significantly increased K_sat. (Tables 3 and 4)

The amount of water near the surface was measured two days after irrigation on 26 Oct 1999. Gravametric water content in the top 3 cm of the soil was significantly reduced when soil was amended with Turface at 2 tons/1000 sq. ft. (Table 3). The soil water measurements near the surface confirmed our observation that the Turface-treated plots usually appeared drier and produced less visible mud compared to the non-amended control plots. This is especially important under intense traffic conditions when the protective grass mat has been worn away and soils are exposed. Rain and routine irrigation to promote turf recovery can often leave the playing surface too wet. Turface-amended soil produced a drier and less muddy surface during the playing season.

This study was conducted on a multi-use sports field that receives traffic from high school football and soccer practice as well as miscellaneous recess activities. The study area received 150 days of use per year and by the end of spring soccer in May there was very little grass cover left on the field. Coring and seeding in June provided a young stand of perennial ryegrass by the start of the 15 August football practice season. Under these conditions of intense traffic where nearly all of the grass was worn away, there was no increase in turf cover in the Turface plots compared to the no Turface control plots.

Turface had a favorable affect on growing conditions by reducing soil bulk density and increasing water movement. Turface also had a positive impact on the soil by reducing compaction and making the playing surface less muddy.

Turf cover was not affected by the use of Turface under the intense traffic conditions of this study.

Table 1. Experimental plot layout of calcined clay tilled renovation. Treatments were applied on November 13, 1997.

Table 2. Treatment listing and respective rates.

Turface applied to plots with topdresser and then tilled with Rotadairon to 4-inch depth.

*Untreated control received no amendment but was tilled with the Rotadairon.

Table 3. Physical characteristics of soil amended with Turface at Ames High School Football Field, 1999.

For water content test, samples were collected two days after irrigation on October 26, 1999.

K_sat, Saturated hydraulic conductivity samples were collected November 7, 1999.

q _m, Gravimetric water content.

Table 4. Physical characteristics of soil amended with Turface at Ames High School Football Field, 2000.

Samples were collected Sept. 26, 2000.

K_sat , saturated hydraulic conductivity.