Golf Course Management

JAN 2017

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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136 GOLF COURSE MANAGEMENT 01.17 pened without an undesirable stimulation of winter shoot growth. Plant uptake of fall-ap - plied N was on the lower side, however, with an average N uptake of about 50% of applied N (within the first month). Spring green-up was also often improved. Late-season root growth was often unaffected by the applica - tion of late-fall N, but application of late-fall N never decreased late-season root growth. Such improvements were seen when late-fall N was applied as late as Oct. 31 (Rhode Is - land) or early November (Illinois, Wisconsin, and Pisa, Italy). No additional benefits were observed with N applications later in the year (December, January). Over a multitude of field studies, no winter injury from late-fall N was ever observed. Given that about half of fall-applied N is not being taken up by the plant, is it prone to loss from the turfgrass system? The answer is yes. There were leaching losses of nitrate- N when N was fall-applied. When soluble N (typically urea) was applied in excess of 1 pound N/1,000 square feet (49 kg N/hec - tare), more nitrate-N was measured in leach- ate than in unfertilized turf. It is generally recommended that fall one-dose applications of soluble N greater than 1 pound N/1,000 square feet be avoided to protect water quality. A lower N application rate is recommended. The authors concluded that the proven turfgrass benefits with late-fall N are mostly seen in improved color and quality. The idea that these late-season applications improve turfgrass photosynthesis and rooting is largely unproven. Results are highly variable across regions and often depend on turf species and seasonal weather. Finally, do not overapply late-fall N. Because the turf is less efficient at taking up N in late fall, excessive N applied at this time can be prone to loss via nitrate- N leaching. Source: Bauer, S., D. Lloyd, B.P. Horgan and D.J. Soldat. 2012. Agronomic and physiologi - cal responses of cool-season turfgrass to fall- applied nitrogen. Crop Science 52:1-10. Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and the editor-in-chief for the American Society of Agronomy. She is a 19-year member of GCSAA. Beth Guertal, Ph.D. guertea@auburn.edu Twitter: @AUTurfFert (verdure) Fall-applied nitrogen (N) for your turf is such a hopeful concept, offering a promising elixir of life for your turfgrass as it heads to - ward a winter of dormancy, off-color and in- activity. (That would pretty much describe my personal February.) The idea is that your last- chance fall application of N would provide fall color retention, prolonged growth and better fall root growth. However, increased concerns about the environmental fate of that N have caused turfgrass managers and researchers to take another look at late-season N, especially in cooler temperature regimes. Turfgrass researchers at the universities of Minnesota and Wisconsin decided to take a look at the existing research on late-season N fertilization of cool-season grasses. This par - ticular paper is a "review of the literature." Rather than doing a new project, the research - ers wrote a summary of all the work that came before, producing a very useful tool for deter - mining what we know about late-season N fertilization of cool-season grasses. Note that late-fall fertilization is not the same as "dor - mant fertilization," which is N applied after plant metabolic activity declines, with that N intended for spring growth. This research paper did not examine dormant fertilization. For fall fertilization of cool-season turf - grasses, the researchers found some fairly standard recommendations. First, late-fall N fertilization was preferred, because early- spring N fertilization in the cool and damp will inhibit root development and prevent the plants from developing tolerance to summer heat and drought stress. Second, late-fall N should be applied after turfgrass shoot growth has ceased. This timing is important, as the plant is still metabolically active, but is no lon - ger actively producing shoot growth. Thus, photosynthates produced in this time period do not go to shoots, but instead move to roots, rhizomes and stolons, helping the plant gain winter hardiness, fall root growth and spring green-up. Third, recommended N rates for this late-fall application ranged from 0.5 to 2.0 pounds N/1,000 square feet (25 to 98 ki - lograms N/hectare), typically about 25% to 50% of the total N fertilizer applied. Agronomically, how did all of this late- fall fertilization work? It worked pretty well. Greatest demonstrated benefits were with improved color and quality late into fall, fol - lowed by earlier spring green-up. This hap- Because the turf is less efficient at taking up N in late fall, excessive N applied at this time can be prone to loss via nitrate-N leaching. It's never too late?

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