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.
Issue link: https://read.dmtmag.com/i/442256
www.stma.org January 2015 | SportsTurf 49 Q&A with Dr. Grady Miller We have typically overseeded our ber- mudagrass sports fields but this year we have "painted" them green. So far we like this approach since we have not needed to mow or fertilize as much and the fields are holding up pretty well. My question is related to fertilization. In the past we fertilized the perennial ryegrass with light rates a couple of times in the fall and then a couple of times in the early spring. Do we need to fertilize the semi-dormant to dormant bermudagrass this fall? Georgia T his is a very good question, one that has been popping up in meet- ings the past few years as turf colorant use (as a replacement for overseeding) has grown in the sports and golf turf markets. Before answering, let's first consider typical overseeding fertiliza- tion practices. Fall overseeding usually involves some level of cultivation toward the end of the warm-season growth period. For some it may be scalping the bermudagrass. For others the preparation may include verti- cutting to remove soil thatch and reduce canopy density for good seed-to-soil con- tact. Many turf managers also may add core aerification toward the end of sum- mer in anticipation of fall overseeding and more concentrated field use. These practices are stressful to the bermuda- grass, so readily available nutrients should be available to provide nutrients to the plant for healthy regrowth. Once the cool-season grass has been sown, irrigation is often applied to ensure even germination. A starter fertilizer may be distributed to supply readily avail- able phosphorus and some additional nitrogen for more rapid shoot growth. If overdone, irrigation can leach nutrients down past the turfgrass roots. To speed up growth and enhance tillering of the cool-season grass, light applications of nitrogen fertilizer may be made through mid-fall. Depending on location and climate conditions, spoon feeding nutri- ents through warmer winter periods may continue until spring when the rates may be increased to promote an even thicker turf density. Due to cool soil temperatures, there is less efficient plant uptake. Cool-season turfgrasses also accumulate nutrients at a greater concentration than the ber- mudagrass. Considering these two factors, the total nutrient needs of cool-season grasses growing under cooler conditions are much lower than what is normally applied to bermudagrass during its pri- mary growing season. In addition, during the cooler months most of the applied nutrients would be absorbed by the more active cool-season grass roots rather than the less active bermudagrass roots. So, what would happen to the nitro- gen fertilizer applied during the cooler months if there was no overseed grass to absorb most of it? Well, if not utilized by soil microbes (later released for plant uptake) or absorbed into plants, then the nutrient could be leached and lost for plant use. So, amounts beyond what can be readily used would not be advised. This is why soluble nitrogen fertilizer rates during the cooler months are generally low (less than half a pound of nitrogen per 1000 square feet per application). An alternative management strategy may be to use slightly higher rates of slow- or controlled-release fertilizer products. But cool-season grasses are not the only grasses that can take up nutrients in the fall. Semi-dormant bermudagrass can still take up available nutrients. But if it is taken up by the bermudagrass, will it cause winterkill? Research work con- ducted in Alabama, Arkansas, Mississippi, North Carolina, and Virginia over the past 20 years suggests that nitrogen fertiliza- tion does not predispose bermudagrass to winter injury as much as was previously thought. Three of those five locations included nitrogen fertilization through October. The one negative to fall fertiliza- tion was a potential increase in spring dead spot, but not increased winter injury. Another noted benefit from fall fer- tilization was a longer green period in the fall. The green color translates into a plant that can continue photosynthesiz- ing and the darker color helps absorb more radiant energy. This encourages re-greening after mild frost events and can aid in greater total carbohydrate pro- duction. This active growth translates into increased wear tolerance as well as the aesthetic benefits of extended green color. The other surprise was that in addi- tion to extending fall color, fall-fertilized bermudagrass typically translated to a quicker and greater amount of spring greenup. This was in the absence of any additional winter or early spring fertiliza- tion. So, fall fertilization also gave spring benefits. There was a time when southern extension specialists did not recommend fertilizing bermudagrass after August. But most do not believe that is good advice anymore. The research and experiences of many turfgrass managers suggest that low rates of nitrogen in the fall will benefit the turf in fall and spring. In essence you were doing that when you fertilized the perennial ryegrass. I would suggest rates of about half what you once used on cool-season over- seed. Fertilization after dormancy would not be suggested, nor would pre-greenup fertilization in the spring. But a little bit may go a long way. ■ ST To ferTilize. or noT. Questions? Send them to Grady Miller at North Carolina State University, Box 7620, Raleigh, NC 27695-7620, or email grady_miller@ncsu.edu Or, send your question to David Minner at Iowa State University, 106 Horticulture Hall, Ames, IA 50011 or email dminner@iastate.edu. Professor, north Carolina State University