Golf Course Management

MAY 2016

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05.16 GOLF COURSE MANAGEMENT 83 achieve water-use reduction goals while still supporting a visually acceptable and func - tional playing surface. Although bermuda- grass has good wear and recuperative ability, the extent to which irrigation levels can be reduced on traffcked bermudagrass fairways in summer without negatively affecting qual - ity, function and recovery has not been fully examined. For the arid Southwest, research - ers (1) have suggested irrigating to 0.8 × ET o in high-traffc situations to avoid stressing the turf. Finally, allowing turf to go dormant by withholding irrigation entirely during water conservation periods may be the only option in more extreme situations in which irrigation is not possible or must be prioritized to greens and tees. In these situations, autumn rainfall becomes critical for achieving turf recovery before the next season. Warm-season grasses generally possess good summer dormancy mechanisms and have been shown to be ca - pable of withstanding and recovering from 60 days of summer drought with no precipitation or irrigation, so long as they are well estab - lished in deep soil (10). The goals of this project were to better quantify effects of traffc and defcit irrigation on bermudagrass fairway performance in the South Central region of the U.S. To accom - plish this, we characterized the response of Tif- way bermudagrass fairways to irrigation levels of 60%, 45%, 30% and 0% × ET o , with and without simulated summer traffc. We also evaluated the effects of successive summers of defcit-irrigated or unirrigated conditions on autumn recovery following resumption of full irrigation levels in September. Methodology This study was conducted during the 2012 and 2013 seasons at the Texas A&M Turfgrass Research Laboratory in College Station, Texas. Field research plots consisted of established Tifway bermudagrass (Cynodon dactylon × C. transvaalensis) grown on a Boonville fne sandy loam soil. The study was arranged in a split-plot design with three replicate plots per treatment. Irrigation main plots (20 feet × 10 feet [6.0 me - ters × 3.0 meters]) were subdivided into two 20- foot × 5-foot (6.0-meter × 1.5-meter) subplots for applying summer traffc to plots. Plots were mowed three times weekly at 0.5-inch (1.2- cm) height throughout the season with clip - pings returned, and received 0.75 pound nitro- gen/1,000 square feet (3.6 grams/square meter) from a 50% methylene urea fertilizer every six weeks from April through August. Irrigation. Irrigation was applied three times weekly from April through August of both years. Irrigation treatments, in diminish - ing order, included: 60% × ET o (warm-season K c ), 45% × ET o , 30% × ET o , and 0% × ET o (unirrigated = rainfall only). A local weather station, meeting the specifcations of the Texas ET Network (http://texaset.tamu.edu) was used to determine ET o replacement irrigation. On-site rain gauges were used for determining contributions from rainfall, which were ac - counted for when determining weekly water requirements. In early September of both years, full (60% × ET o ) irrigation levels were resumed in all plots to promote and evaluate recovery from water stress. Traffc stress. To simulate summer traffc stress in this study, irrigation main plots were subdivided with half of each plot receiving traffc (six passes weekly) during July and Au - gust from a modifed Cady traffc simulator (11) equipped with soft-spike golf cleats. Green cover. Plots were analyzed for per - cent green cover using the Karcher macro and SigmaScan digital image analysis software (8). Digital images were taken twice monthly from May through December using a Nikon Coolpix digital camera mounted on a 0.6- meter × 0.6-meter (1.9-foot × 1.9-foot) square light box that was randomly positioned within each plot. The light box cancelled out outside light and created uniform light within the box. For reference, >75% green cover was gen - erally found to correspond well to minimally acceptable visual turf quality ratings. Divot recovery. The study also assessed divot recovery time in response to irrigation. In July of each year, a modifed edger consist - ing of a series of stacked blades was used to create four uniform divots (2 inches wide × 3 inches long [5.0 cm × 7.6 cm]) in each plot (4). Divots were backflled with either sand or sand/peat (90:10 volume:volume) infll and analyzed after 45 days via digital analysis of light box images to evaluate regrowth in the divoted areas. As an indicator of turf stress, refective canopy temperatures were also measured during the midafternoon hours on cloudless days using an infrared hand-held tempera - ture gauge. Root growt . In September of both years, root growth within the upper 12 inches (30.4 cm) of soil was evaluated using a 2-inch (5-cm) diameter hydraulically driven sampling probe. Root/soil samples were rinsed to remove soil and oven-dried for 72 hours at 149 F (65 C) before weighing. In July and August of both years of the study, a modifed Cady traffc simulator equipped with soft-spike golf cleats was used to simulate summer traffc stress. Half of each plot received six passes weekly. Photos by Ben Wherley

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