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. Axis, Profile, Zeolite, and Zeopro are inorganic amendments that will be compared with the organic amendment 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.

The sloped green matured and filled in during the summer of 1998. By August there was 100 percent turf cover and approximately 0.5-cm of thatch. On 25 September 1998 the green was severely verticut. A 0.5-cm depth of topdressing material was immediately applied for each treatment following verticutting. The green was mowed at 0.25 inches during the fall and was covered on 1 December 1998 with an Evergreen Grow Blanket for winter protection. The green was showing signs of winter desiccation by late January, but there were no visible differences among treatments. By 1 April it was apparent that the turf was severely damaged by winter desiccation and there were still no differences among treatments from winter injury or spring green-up. On 1 April 1999 the green was verticut, reseeded, and plugs moved, within treatments, into the most severely damaged knoll areas of the green. Mowing height was raised to 0.45 inches and gradually lowered to 0.2 inches by 23 August 1999. Treatments were topdressed with 0.2 inches of material on 26 September 1998. Topdressing treatments were applied every two weeks from 14 May to 30 September for a total of 1.0 inch of topdressing in 1999. To smooth the green’s surface and depressions between plots, the entire green was topdressed with 0.1 inches of the original sand and drug across all plots on 25 Oct 1999. The entire green was fertilized with a total of 4.4 lb N/1000sq.ft., 2.5 lb P₂O₅/1000sq.ft., and 3.6 lb K₂0/1000sq.ft. Since Zeopro contains additional nutrients it received an additional 1 lb N/1000sq.ft., 0.5 lb P₂O₅/1000sq.ft., and 6 lb K₂0/1000sq.ft. Turf quality, color, and dry spots were rated throughout the summer on a scale of 0-9, 9=best turf.

Table 1. Organic and inorganic amendments applied to the sloped putting green as topdressing treatments.

Table 2 shows the quality ratings for 1999. During most of the growing season Zeopro showed better turf quality than all other topdressing treatments because of the improved turf color that was associated with the additional nitrogen in this "loaded product". Also under more favorable conditions, i.e. swale and cool areas, Zeopro produced better turf quality.

In the knoll area, where stress increased, turf performance among treatments would change as the result of two planned dry down periods. During the first stress period Zeopro had significantly better quality than Zeolite and the control. At this same time Axis was better than Profile. During the second water stress period turf was showing considerable wilt with no differences between treatments. Nine days into the irrigated recovery period, 16 September 1999, Axis was better than Profile, Zeopro, and the control. Profile and Zeopro had significantly lower quality than all other treatments. The advantage in turf quality gained under non-stress conditions by Zeopro was lost during the irrigated recovery period that followed two periods of moisture stress. The Zeopro treatment totaled 5.4 lb N/1000sq.ft. while all other treatments had only 4.4 lb N/1000sq.ft. It is possible that the extra 1 lb N/1000sq.ft. could have made turf appear better during most of the summer, but also predisposed the grass to more injury as evident from the lower quality ratings following the dry down and recovery period. On 14 October 1999, 37 days into the recovery period Profile had recovered to have the best turf quality although the differences among treatments were not significant.

The realistic conditions of the SRG have demonstrated treatment differences that may not have been apparent on a flat research green. It is important to simulate realistic conditions whenever possible in our turfgrass research programs.

Table 2. Turfgrass visual quality in four microenvironments of a sloped green treated with inorganic amendments in 1999.

*0-9 scale, 9 = best.