A sloped research green (SRG) was constructed and established with ‘Crenshaw’ creeping bentgrass at the Horticulture Research Center, Ames, IA in July 1997 to evaluate bentgrass management under difficult and variable growing conditions. The objective of this project was to evaluate organic and inorganic amendments applied as topdressing. Iowa State University, Iowa Golf Course Superintendents Association and the Golf Course Superintendents Association of America fund this project. The SRG was erected to simulate the undulating topography that occurs on many putting greens - as opposed to a typical flat research green. The sand based portion of the SRG is 100 ft by 40 ft by 1 ft. The subgrade, gravel blanket, and sand rootzone all follow the same contour. The 12-inch sand rootzone contains no amendment and is positioned over a 4-inch gravel blanket with 4-inch drain lines. The SRG has four distinct micro-environments that will be simultaneously evaluated for nine different treatments. The micro-environments are: 1) cool slope - this 7.0% slope faces north and should be cooler in the summer but also colder in the winter, 2) knoll - the crown of the green is expected to have the most potential for scalping and dry spot injury in the summer, 3) hot slope - this 6.6% slope faces south and is expected to generate high surface temperatures, and 4) swale - the low portion of the green is expected to have excessively wet conditions. No amendments, organic or inorganic, were used to construct the 12-inch rootzone. The sand has a pH of 8.2 and is calcareous. Topdressing treatments will be routinely applied to 40 ft. by 6 ft. plots. The long and narrow plots are situated so that each treatment covers all four distinct micro-environments on the green. The five topdressing treatments are listed in Table 1. The inorganic amendments Axis, Profile, Zeolite, and Zeopro are being compared with the organic amendment sand plus Dakota Peat. Axis is a diatomaceous earth, Profile is a porous ceramic clay, Zeolite is an aluminosilicate mineral, and Zeopro is a nutrient loaded Zeolite. All of the products claim to improve cation exchange, and nutrient and water holding capacity.

Samples for soil nutrition were collected from three locations of the slope green; north slope, knoll, and swale. Since the topdressing materials were located in the top 2.5 cm, samples were collected from two different depths, 0 to 3.35 cm and 3.35 cm to 12.5 cm. Living roots were picked out and the sample before air drying and screening through a 2 mm sieve. Soil fertility analysis was conducted by Harris Lab, Lincoln, Nebraska. Light and frequent applications of topdressing treatments have resulted in 3.35 cm (1.32 inches) of topdressing being applied from 1998 through September 2000. From May through September 1.25 cm (.5 inches) of topdressing was applied from each treatment. Zeopro is a loaded amendment that contains additional N, P, and K. Table 1 shows the total amount of nutrition applied for each treatment in 2000. Similar to 1999, in 2000 water was restricted to impose artificial water stress. The first water stress was from 9 to 18 August 2000 and the second water stress was from 1 to 6 September 2000. Turf color and percent of the plot area covered with dry patches was evaluated every two weeks. Volumetric water content was measured at the 5 cm, 10 cm, and 20 cm depth before and after water stress.

The topdressing treatments applied in this study are listed in Table 2. A program of light and frequent application of topdressing has resulted in a total topdressing dept of 3.35 cm (1.32 inches) applied from 1998 through September 2000.

Table 3 shows the turf color ratings and percent of area covered with dry patches during the spring and summer of 2000. The first water stress period occurred from 9 to 18 August 2000 by completely restricting irrigation. A second water stress period occurred from 1 to 6 September 2000 while maximum air temperature was above 32° C from September 1-3. In 2000 none of the inorganic topdressing treatments had an effect on the amount of dry patch compared to the sand/peat control. The only notable difference occurred in the spring of 2000 when Zeopro had significantly more dry patch (46%) compared to Zeolite (13.3%) and Axis (9%).

Table 4 shows the soil nutrient levels in the spring of 2000. Zeolite and Zeopro resulted in very high levels of K and twice as much Na compared to the control, Axis, and Profile treatments.

The realistic conditions of the SRG have demonstrated treatment differences that may not have been apparent on a flat research green. In 2000 the knoll area showed differences in dry patch that were not apparent on the north slope, south slope, and swale area of the green with respect to the amount of visible dry patch. It is important to simulate realistic conditions whenever possible in our turfgrass research programs.

Table 1. Amount of inorganic amendments and fertilizers applied in 2000.

Table 2. Organic and inorganic amendments applied to the sloped putting green as topdressing treatments.

Table 3. Turfgrass color and occurance of dry patch and in 2000 for four microenvironments of a sloped green treated with inorganic amendments.

Table 4. Spring 2000 soil nutrition in the surface topdressing zone (0-3.35 cm) compared to the lower portion of the original rootzone sand (3.35-12.5 cm).