Black layer (BL) has reduced the quality of many putting greens since the 1980s. Initially, the nature of BL was unknown. Research established that BL was sulfide (S2−) formed in response to low redox. Its formation was linked to dissimilative sulfate reduction using labeled sulfate (35SO4 2−). The objective of this study was to see if elemental sulfur (S0) reduced to S2−. When labeled sulfur (35S0) with a specific activity of 3.7 × 104 Bq·mg−1 was added to soil from a green with BL in a reaction vessel kept at a low redox potential, it reduced at a per-minute rate of 5.3 nmol·cm−3, resulting in accrual of labeled hydrogen sulfide (H2 35S) and acid-soluble sulfide (AS35S). Nearly 32% of the 35S0 reduced to labeled sulfide (35S2–) in 24 h. Adding S0 to greens with low redox may result in rapid formation of S2– and an accelerated rate of BL development. Avoiding this requires limiting the input of S0 or encouraging high soil redox through chemical or physical means such as fertilizing with nitrate (NO3 –) and aerifying. This is the first report implicating S0 reduction as a source of BL development in putting green soil.
William L. Berndt and Joseph M. Vargas Jr
W.L. Berndt and Joseph M. Vargas Jr.
Black layer has been associated with a severe decline in the quality of turf on putting greens. It was suggested that the black layer results from dissimilatory sulfate (SO4 2–) reduction. This study was done to determine if SO4 2– reduction occurs in an existing black layer. Radioactive 35SO4 2– was used to calculate the rate of SO4 2– reduction in intact soil cores taken from an existing black layer in a `Penncross' creeping bentgrass (Agrostis palustris Huds. `Penncross') putting green. When 10–3 M 35SO4 2– with a specific activity of 1.554 × 105 Bq·mg–1 SO4 2– was injected into a core it reduced to sulfide (35S2–) at a mean rate of 7.1 nmol sulfur (S)/cm3 soil/d. Injecting azide (N3 –) or molybdate (MoO4 2–) at 10% w/v with the label reduced the rate of SO4 2– reduction to 0.03 and 0.01 nmol S/cm3 soil/d, respectively. The effect of N3 – confirmed that reduction of SO4 2– was biological, while the effect of MoO4 2– confirmed that the entities responsible for the reductive cycling were sulfate-reducing bacteria (SRBs). This was the first proof that biological reduction of SO4 2– produces S2– in a black layer from a creeping bentgrass putting green. It was concluded that the respiration of indigenous SRBs was linked to development of this black layer. Thus, a key to successfully controlling black layer in putting greens must involve regulating the respiratory activities of SRBs.
Thomas O. Green, Alexandra Kravchenko, John N. Rogers III and Joseph M. Vargas Jr.
A major concern with many creeping bentgrass (Agrostis stolonifera) putting greens is annual bluegrass (Poa annua) invasion. The study was designed to garner data regarding the depth of soil removal needed to reduce annual bluegrass seedling emergence in a newly renovated putting green. Research was conducted in different seasons (summer and fall) to evaluate seedling emergence across five soil removal depths in four sampling sites. Cores were collected from four golf courses in southeastern Michigan, subdivided into different soil removal depths, potted in sterile soil media, and established in a growth chamber. Results suggest that excavating soil to a depth of 1.0 inch or, more prudently, to a 1.5-inch depth could minimize annual bluegrass competition in a creeping bentgrass putting green. Annual bluegrass emergence was observed to be greatest in the upper soil depths (0.5–1.5 inches) in both seasons, with minimal emergence (<1.1 plant/0.2 ft2) below the 2.0-inch soil removal depth treatment.
Thomas O. Green, John N. Rogers III, James R. Crum, Joseph M. Vargas Jr. and Thomas A. Nikolai
Results suggest that sand topdressing was more consistent at reducing dollar spot (Clarireedia jacksonii) in fairway turfgrass more so than rolling. This practice could be an effective cost-saving alternative to reduce frequent fungicide applications. Research was conducted from 2011 to 2014 on a simulated golf fairway and examined dollar spot severity responses in a mixed-stand of creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua ssp. reptans) to sand topdressing and rolling. Treatments consisted of biweekly sand topdressing, rolling at three frequencies (one, three, or five times weekly), a control, and three replications. Infection was visually estimated. Sand topdressing significantly (P < 0.05) reduced disease up to 50% at the peak of the dollar spot activity in 2011, 2013, and 2014. Results on the effects of rolling on dollar spot were inconsistent.