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 14 of 51

www.spor 15 December 2017 // will need to be mown. Turfgrass regrowth is correlated to not only the residual leaf area after mowing but also the carbohydrate food reserves in the remaining verdure; verdure is essentially how much turf is left above the soil surface after mowing. Grass clippings The management of grass clippings is another important and often overlooked aspect of mowing. At one time, the practice of returning grass clippings was thought to contribute to thatch accumulation and, as a result, clippings were routinely collected. Moreover, grass clippings can be collected to prevent the unsightly clumps of clippings when wet and/or long turf is mown. A decrease in landfi lled grass clippings and increase in clippings being returned to turf has occurred for a multitude of reasons. First, 25 states have banned yard trimmings from landfi lls. Second, concerns over thatch production due to returning grass clippings have since been dismissed due to research demonstrating the rapid decomposition of grass clippings. Third, returning grass clippings improves the color of turfgrass compared to removing clippings. In fact, reducing N fertilization by half will not decrease turfgrass color when clippings are returned. Other researchers have noted increases in nitrogen use effi ciency, nitrogen uptake, and overall dry matter yield as the benefi ts of returning grass clippings. Lastly, returning grass clippings to a turfgrass system over an extended period of time (>25 years) has been will reduce nitrogen requirements by 50% through the accumulation of soil organic nitrogen over time. Research was recently completed at Purdue University to better understand the impact of turfgrass species and cultivar selection as well as clippings management on mowing requirements. The objectives of this research were to determine: (i) the number of required mowing events when mowing weekly versus using the one-third rule, (ii) the infl uence of returning grass clippings on mowing requirements, dry matter yield, and leaf nitrogen content; and (iii) if turfgrass species and cultivars with differing growth rates infl uence mowing requirements, dry matter yield, and leaf nitrogen content. In this irrigated fi eld experiment, mowing events were signifi cant for all main effects (i.e., species, growth rate, mowing frequency, and grass clippings management) in both years of the experiment. Tall fescue required more annual mowing events than Kentucky bluegrass. The fast-growing cultivars required the greatest number of annual mowing events (25 in both years), which was followed by the moderate-growing cultivars (23 in both years); the slow- growing cultivars required the fewest mowing events. Mowing based on the one-third rule (18 events in both years) reduced the number of mowing events compared to weekly mowing, and returning grass clippings resulted in a greater amount of mowing events versus collecting clippings. In an evaluation of the interaction of the factors in our experiment, the infl uence of mowing frequency is readily apparent. All of the weekly-mown plots, regardless of species, growth rate, or grass clippings management, except for the slow-growing Kentucky bluegrass plots, required more mowing than all of the plots mown by one-third rule. The slow-growing Kentucky bluegrass cultivar mown by the one-third rule with clippings collected had the fewest mowing events in 2013, with only 12.3 annual mowing events. For the 2-yr cumulative dry matter yield of the weekly- mown plots with clippings collected, species, growth rate, and the species by growth rate factors were all signifi cant. Tall fescue had a greater dry matter yield than Kentucky bluegrass. The fast- growing cultivars had the greatest dry matter yield, followed by the moderate-growing cultivars; the slow-growing cultivars had the lowest dry matter yield. For the interaction of species by growth rate, the fast- and moderate-growing tall fescue cultivars had a greater dry matter yield than all of the Kentucky bluegrass cultivars. However, the slow-growing tall fescue cultivar had a similar dry matter yield to that of the fast-growing Kentucky bluegrass cultivar. The fast-growing Kentucky bluegrass cultivar was also similar to the moderate-growing Kentucky bluegrass cultivar, and the slow- growing Kentucky bluegrass cultivar had the lowest dry matter yield of all treatments. More findings It was evident from out experiment that mowing requirements can be infl uenced by a number of factors. By selecting slow-growing turfgrasses, mowing requirements can be reduced for the life of the turf. Unfortunately, slow-growing cultivars can be slower to establish and recover from injury. Future cultivar experiments on growth rate would be benefi cial for both the establishment of low-maintenance areas where reduced mowing is desired and also for high traffi c areas such as athletic fi elds where quick recovery is desired. A fast-growing tall fescue cultivar photographed in May. It is the weekly mown plot with clippings returned and illustrates that mowing once weekly is insufficient during periods of rapid growth.

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