December 2017

SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.

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Page 17 of 51

www.spor 18 // December 2017 Our dry matter yield values were comparable to previously published tall fescue and Kentucky bluegrass data from the same geographic location that received similar annual nitrogen rates. Furthermore, our fi ndings support previous research that indicates that returning grass clippings increases dry matter yield. Dry matter yield increases of 27 to 45% were obtained in our study. The infl uence of turfgrass species and growth rate on dry matter yield was also apparent in our study, and our data supports previous fi ndings that tall fescue generally produces greater dry matter yield values than Kentucky bluegrass. Furthermore, others have noted greater dry matter yield values for faster-growing cultivars, which was observed across all species in our experiment. Cool-season turfgrasses are often cited to have a bimodal seasonal growth pattern that includes a strong fl ush of growth in spring, cessation of growth over summer, and moderate growth in autumn. However, our dry matter yield values were highest in spring, intermediate in summer, and lowest in autumn both years. It is logical that our spring dry matter yield values were the highest, given that approximately two-thirds of tall fescue growth is said to occur during the spring and that as much as 75% of the annual growth for Kentucky bluegrass can occur by early summer in unirrigated areas. However, the autumn fl ush of growth was not readily apparent in our irrigated study. Our dry matter yield measurements did not account for plant root growth or tillering, which may be another reason why our growth measurements are not entirely consistent with the commonly accepted bimodal seasonal growth pattern of cool-season turfgrasses. Further, the cool autumn weather of late September through to November dramatically slows shoot growth and reduces the overall autumn dry matter yield. It is during these cool autumn periods that cool-season grasses such as Kentucky bluegrass build a carbohydrate storage reserve rather than directing energy to leaf growth. Additionally, our experimental area was irrigated, so summer yields were likely to have been higher than nonirrigated turf, which may have masked the fall flush of growth typical of cool- season grasses. Growth potential and yield estimates are a current topic of interest among turfgrass scientists, as this information is critical to not only refi ne mowing practices but to also nutrient recommendations. Growth rate is dependent on season, temperature, rainfall and irrigation, nitrogen, PGRs, and other factors such as soil nitrogen mineralization. These factors still need explored further in order for us to predict and model turfgrass growth. Increased leaf nitrogen was the result of returning grass clippings in our study and highlighted the important role that grass clippings management plays in nitrogen cycling in turfgrass systems. To reduce nitrogen fertilization requirements, turfgrass managers should return grass clippings when mowing. The results of this study highlight the importance of turfgrass selection (i.e., species and cultivar), mowing frequency, and grass clippings management for annual mowing requirements. This research also provides specifi c management practices that homeowners and professional turfgrass managers can use to reduce their mowing requirements, namely mowing by the one-third rule and selecting slow-growing cultivars of the turfgrass species best adapted to their location. While selecting slow-growing cultivars will help reduce mowing frequency, their use should be limited to low-use (traffi c) fi elds. Use cultivars with faster growing (recovery) rates and proven traffi c tolerance in high-traffi c fi elds to improve chances for success. /ST/ This research was supported by the United States Golf Association and the Midwest Regional Turf Foundation. A full description of this research was published recently in Crop Science: Law, Q.D., C.A. Bigelow, and A.J. Patton. 2016. Selecting turfgrasses and mowing practices that reduce mowing requirements. Crop Sci. 56:3318-3327. Aaron J. Patton PhD, is professor of horticulture and turfgrass extension specialist at Purdue University. Quincy Law, MS, is a PhD student in the Department of Horticulture and Landscape Architecture at Purdue. Close-mown fields like this one need more frequent mowing than the treatments tested in our study that were mown at 2.75 inches.

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