Surface organic matter in bermudagrass greens: A primary ... - GCSAA

RESEARCHgram) CEC because little dead organic matterwas present at CEC sites and essentially no claywas found. Thus, some organic matterenhances CEC status.Thatch or mat?Is the surface zone of high organic matterthatch or mat? Thatch is a zone of deadand living organic matter without appreciablesand integrated into it. Sometimes athatch zone created during grow-in becomesburied and remains as a thatch layer problem.Mat is an organic zone that has considerablesand integrated within it, with sand as thedominant matrix.From field observations, it appears that thequantity of sand topdressing sufficient to maintaina uniform, stable surface with goodputting speed is often less than the quantity oftopdressing required to create a true mat. Thesurface zone of many greens appears to be a“near mat,” but with insufficient sand to negatethe organic matter. When sand is not maintainedas the primary matrix, the result is considerablesand floating in the organic matter. Inthat case, the organic matter, not the sand, controlsthe aeration and moisture status.Management practicesSurface organic matter accumulation ismanaged by a combination of the followingpractices.Dilution. Dilution of the surface organicmatter through aggressive topdressing, especiallyin combination with hollow-tine aerationand venting operations, is the backboneof any successful program. A recent article (5)provides excellent options and guidelines thatare appropriate for bermudagrass and creepingbentgrass greens. The suggested targetrange for annual topdressing on many sites,40-50 cubic feet/1,000 square feet (121.9-152.4 cubic meters/hectare), is based on historicalrates that were used until a few yearsago when ultralight but more frequentapplications became the norm and resultedin less total sand applied.Using adequate hollow-tine core aerationoperations and venting operations to maintainmacropores across the surface organic matterzone at all times is important for ensuringoxygen diffusion across the zone to reachunderlying roots. Developing and maintainingdeeper roots allows less-frequent irrigationso that the surface zone has the opportunityto dry somewhat, which greatly improves oxygenstatus within the zone. If topdressing andFigure 3. Greens with poor air circulation and drainage often exhibit excessive organic matter in the surface layer.Excessive organic matter induces high moisture and lower oxygen content in the root zone, inhibiting microbial decompositionof the organic matter.cultivation operations are insufficient to controlthe surface organic matter zone quickly,the result will be shallow roots, which requirelight, frequent irrigation and frequent spoonfeeding.This situation fosters even moreorganic matter accumulation.Surface pH levels. The surface pH shouldbe higher than 5.5 to allow adequate bacterialpopulations for organic matter decomposition.One practice that has beenrecommended for bermudagrass decline hasbeen the use of acidifying fertilizers. Oneresponse that occurs on soils with at leastsome clay is that at pH below 5.5, more solublemanganese is often observed. However,on sands with CEC from primarily organicmatter, this is not the case. Adequate manganeseis important for suppressing take-allpatch (3,4). If the surface pH is below 5.5,the reason for a low pH should be determined.Water acidification can cause a lowpH at the surface while also adding appreciablesoluble sulfur. If anaerobic conditionsstart within or below the surface organic matterzone, the presence of soluble sulfur willgreatly increase the chance for black layer (6).Take-all. On sites with an existing organicmatter problem and a history of take-all, itmay be worthwhile to test not only foliar applicationsof manganese, but also some granularapplications to achieve higher manganese levelswithin both the plant and organic zone.Secondary stresses. If excessive organicmatter stimulates a particular secondarystress, then practices to control the secondarystress will be of immediate concern.Photo courtesy of R.N. CarrowSummaryIn summary, the new ultradwarf bermudagrassesused on putting greens have a strongtendency to accumulate organic matter withinthe surface zone, and certain stresses are frequentlyobserved on these grasses (decreasedrooting over time, root-rot pathogens, others).The challenge for the superintendent is toidentify the primary or underlying stresses andmanage them aggressively.References1. Carrow, R.N. 2004. Surface organic matter in bentgrassgreens. Golf Course Management 72(5):96-101.2. Duncan, R.R., and R.N. Carrow. 2000. Seashorepaspalum: The environmental turfgrass. Wiley,Hoboken, N.J.3. Elliot, M. 2001. Got root rot? Don’t panic. Florida TurfDigest March/April 20-23.4. Heckman, J.R., B.B. Clark and J.A. Murphy. 2003.Optimizing manganese fertilization for the suppressionof take-all patch disease on creeping bentgrass.Crop Science 43:1395-1398.5. O’Brien, P., and C. Hartwiger. 2003. Aeration andtopdressing for the 21st century. USGA GreenSection Record 41(2):1-7.6. Unruh, J.B., and S. Davis. 2001. Diseases and heatbesiege ultradwarf bermudagrasses. Golf CourseManagement 69(4):49-54.Robert N. Carrow, Ph.D. (rcarrow@griffin.uga.edu), is aprofessor of turfgrass science and a research scientistat the Georgia Experiment Station, University of Georgia,Griffin. Carrow was an instructor at GCSAA educationseminars in San Diego, and he is one of the subjectmatter experts for GCSAA’s online W.A.T.E.R. course.May 2004GCM 105