Landscape Architect & Specifier News

JUL 2018

LASN is a photographically oriented, professional journal featuring topics of concern and state-of-the-art projects designed or influenced by registered Landscape Architects.

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July 2018 73 Left: Over the course of two summers, plots of bermudagrass were subjected to varying degrees of deficit irrigation to help determine the minimum amount of irrigation needed to maintain acceptable turfgrass quality for the entire warm season, and the minimum amount of irrigation required if lower turfgrass quality is suitable for varying periods of time. Right: Before the two studies, two to four catch-can tests were carried out per plot, with 24 catch-cans in each plot to determine low-quarter irrigation distribution uniformity (DULQ) and precipitation rate of each plot. The first summer the 12-plot average DULQ and precipitation rate were 75% and 1.10 inches /hour, respectively. The second summer the numbers were 74% and 1.10 inches/hour. (Editor's note: The following article was excerpted from a research paper from a team led by Robert Green, Ph.D., the entirety of which can be found at https://tinyurl.com/ yd2l2cxy ) Common bermudagrass and hybrid bermudagrass are very popular turfgrass species in Southern California and in warm climates across the southern United States. The growth characteristics, overall appearance and adaptation of bermudagrass to these climates deliver a quality turf that will respond well to a range of maintenance levels. "Deficit irrigation," the practice of irrigating bermudagrass below optimal conditions (technically, below crop evapotranspiration under standard conditions, or ET crop ), allows soil and turfgrass tissue to gradually dry during summer, which helps conserve water, maintain water budgets, save on operating costs and more. Depending on the degree of deficit, bermudagrass can continue to provide sufficient growth and recuperative ability, and acceptable (compared with minimally acceptable or lower) turfgrass quality during the entire warm season. Since deficit irrigation has become more widely used, two questions have arisen: What is the minimum amount of irrigation needed to maintain acceptable turfgrass quality for the entire warm season, and what is the minimum amount of irrigation required if lower turfgrass quality is suitable for varying periods of time? The Study The primary objective of this research was to begin to defne irrigation requirements for a range of bermudagrass visual quality and color ratings during the warm season (average rating for an entire warm season ranges from 4 to 7). Ratings were on a scale of 1 to 9 (where 1 = dead or brown; 5 = minimally acceptable; 6 = acceptable; and 9 = maximum quality or color). This study was conducted from June to September over two summers on 12 well- established GN-1 hybrid bermudagrass plots located at the Center for Turf, Irrigation and Landscape Technology at California State Polytechnic University, Pomona in Pomona, Calif. Plots were located in full sun. Each plot was individually zoned and controlled and had a rotating nozzle sprinkler at each of the four corners. Prior to the study, plots were well irrigated to ensure uniform soil water content in the 0- to 12-inch root-zone depth.

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