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TURFGRASS NUTRITION What’s Old is New Again
Photo 1: Virginia Tech has led research that verifies both the presence and the concentrations of hormones in seaweed extracts and how those compounds can promote turfgrass root development.
By Richard Schmidt, Ph.D., Professor Emeritus; Xunzhong Zhang, Ph.D., Research Associate Professor; and Mike Goatley Jr., Ph.D., Professor and Extension Turfgrass Specialist, Virginia Tech
(Note from Mike Goatley: Professor Emeritus Dick Schmidt remains very much engaged in keeping up with the world of turfgrass research even now in his 10th decade on this planet! I asked him to please put his unique perspectives on the evolution of turfgrass nutrition programs over the past 60+ years and the ways that the research and application programs have evolved in print. Dr. Zhang and I chimed in with some of our perspectives, but Dick led the development of what is a nice review of nutrition and strategies that allow a turfgrass manager to get the most out of a fertility program and produce a healthy, functional turfgrass plant.)
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Photo 2: The April greening response of trafficked bermudagrass where 0.25 lb nitrogen per 1000 square feet rates of soluble nitrogen were applied monthly in the fall through mid-October (foreground block), mid-September (middle), and no fertilization past mid-August (background).
ecently a USGA agronomist indicated that it is desirable to keep bentgrass golf putting greens a bit yellow during hot weather. For Dr. Schmidt, this brought back memories of when he first started studying turfgrass ecology under Professor Burt Musser at Penn State and frequently accompanied him when he toured some of the golf courses in Pennsylvania. It was during some of these trips that Dick recalls hearing senior golf course superintendents state, “Keep the bentgrass on the yellow side during the hot season.” Dr. Goatley notes that during his career, a constant phrase uttered by turfgrass managers that he equates with Dick’s recollection of the value of off-color bentgrass during summer stress is to keep the grass “lean and mean.” Studies regularly show that these mid-20th century superintendents had valid reasoning for avoiding aggressive nitrogen fertility programs on bentgrass during summer stress, and that the recent comment by the USGA agronomist was most observant. Data show that high nitrogen fertility programs on bentgrass greens did enhance green color prior to and during hot weather; however, top growth was exacerbated causing a reduction in carbohydrate content. High nitrogen applications consequently reduced root production. Additional environmental stresses (heat and drought stress primarily) increased accumulation of metabolic toxic oxygen species (free radicals, more on this later in this article) which may damage plant lipids, proteins and other organic components, the literal building blocks of your turfgrass tissues. These internal stress responses reduce photosynthetic efficiency and eventually lead to cell death (and visible loss of turf). Although turfgrasses possess their own antioxidant defensive systems the levels may not be adequate to reduce damage that is exacerbated with the high nitrogen applied under these additional stresses. Considering the color, the density, and the height and frequency of clipping of bentgrass that the golfer demands, how does one effectively manage quality turf? First, one needs to assure all the requirements of a healthy soil are met: pH, aeration, appropriate levels of organic matter, and sufficiency levels of all required nutrients other than nitrogen. Then the answer for nitrogen management is to follow nature’s lead in carbohydrate ac-
18 | VIRGINIA TURFGRASS JOURNAL November/December 2022 www.vaturf.org
