1999 Iowa Turfgrass Research Report

Turf management practices are usually applied uniformly across a putting green. Research greens are usually perfectly flat and uniform. However the actual greens are not flat and problem areas are not uniform. A meaningful interpretation of research results depends on how close the research situation is to the real world. A sloped research green (SRG) was constructed at the Horticulture Research Center, Ames, IA, in July 1997 to evaluate bentgrass management under difficult and variable growing conditions. Construction of the green was funded by Iowa State University, the Iowa Golf Course Superintendents Association, and the Golf Course Superintendents Association of America. The objective of this project was to evaluate organic and inorganic amendments applied as topdressing.

The SRG was erected to simulate the undulating topography that occurs on many putting greens - as opposed to a typical flat research green (Figure 1). A 12-inch sand rootzone containing no amendments, organic or inorganic, was positioned over a 4-inch gravel blanket with 4-inch drain lines. The subgrade, gravel blanket, and sand rootzone all follow the same contour. The SRG has four distinct microenvironments that will be simultaneously evaluated for nine different treatments. The microenvironments 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. To our knowledge, this type of sloped green project has never been used for putting green research.

The sand for rootzone construction has a pH of 8.2 and is calcareous. The green was seeded with Crenshaw creeping bentgrass in September 1997. 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. The experimental area measures 100 ft by 40 ft. The main experiment contains five topdressing treatments in a complete randomized block design. Each treatment unit (plot) measures 40 ft by 6 ft. The long and narrow plots are situated so that each treatment covers all four distinct microenvironments 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 a aluminosilicate mineral, and Zeopro is a nutrient loaded zeolite. In another experiment, Bio-Flex-A-Clay was used as topdressing at three different rates 5 lb/1000 ft², 10 lb/1000 ft², 20 lb/1000 ft². Bio-Flex-A-Clay is a polymer coated sand with a kelp material incorporated. All of the products claim to improve cation exchange, and nutrient and water holding capacity.

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 maintained at a 0.25-inch cutting height and covered during the winter with a Covermaster cover for winter protection. Moderate-to-severe winter desiccation damage was observed when the protective cover was removed in April. Most of the injury occurred on the knoll and south facing slope near the knoll of the green. The entire green was reseeded with 2.0 lbs. Of 'Crenshaw' creeping bentgrass in May. There were no apparent differences among treatments based on winter injury. An additional 1.5 cm of topdressing is targeted for the entire 1999 growing season. Topdressing will be applied in light and frequent applications (Table 2).

Routine traffic, fertilizer and mowing will be applied. Dry condition will be simulated by restricting irrigation on a temporary basis from July through August. Turfgrass survival and loss will be related to the treatments and micro climate areas.

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

	Topdressing Treatment	Calcareous Sand	Inorganic Amendment	Organic Amendment
		% by volume
1	sand + Dakota peat (control)	90	-	10
2	sand + Axis	80	20	-
3	sand + Profile	80	20	-
4	sand + Zeolite	80	20	-
5	sand + Zeopro	80	20	-

Table 2. Amount and date of topdressing application.

Topdressing Treatment		Topdressing depth (cm)
		9-25-98		5-14-99		6-2-99		6-11-99		6-25-99	7-9-99	7-23-99	8-6-99	8-20-99
1	sand + Dakota peat (control)		0.5		0.2		0.2		Target topdressing depth of 0.2 cm for each treatment and date.
2	sand + Axis		0.5		0.2		0.2
3	sand + Profile		0.5		0.2		0.2
4	sand + Zeolite		0.5		0.2		0.2
5	sand + Zeopro		0.5		0.2		0.2

ISU Horticulture:Publications:1999 Turfgrass Report

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