Date of Award
Doctor of Philosophy
Adam W Thoms
Turfgrass culture and management practices have improved drastically over the past 50+ years due to readily available information and products that enable turfgrass managers to investigate, mitigate, and solve many turfgrass management conundrums. While the turfgrass manager now better understands how to regulate and apply quantifiable inputs, it remains that abiotic factors or conditions are mostly beyond their control. Because of this, further investigation of abiotic stressors on turfgrass health is necessary. This dissertation is organized into two chapters involving turfgrass traffic tolerance and one chapter focusing on compost-induced salt stress during turfgrass establishment.
Athletic field safety is a top concern of field managers and athletic directors across all field sports. Increased usage of fields with traffic-sensitive cultivars can result in reduced turf cover and therefore decreased field safety. While most Kentucky bluegrass (Poa pratensis L.; KBG) cultivars have strong recuperative potential, significant cultivar differences in ability to withstand traffic exist. The study discussed in Chapter 2 was conducted to determine whether leaf epidermal cell sizes predict differences in KBG cultivar traffic tolerance. Upper epidermal cell size, lower epidermal cell size, and intercellular void space (IVS) were measured on three traffic-tolerant and three traffic-sensitive KBG cultivars from the 2011 National Turfgrass Evaluation Program KBG traffic trial. Transverse sections of leaf tissue were fixed in an acid/alcohol solution and embedded with paraffin prior to sectioning for imaging by light microscopy. Cell size was determined by counting cells per unit area from light microscopy images. Leaf upper and lower epidermal cell size was not a predictor of traffic tolerance. Differences were measured in IVS at the cultivar level and at the traffic-sensitive versus traffic-tolerant grouping contrast level. Traffic-tolerant cultivars exhibited larger IVS (2,823 µm2) than traffic-sensitive cultivars (1,112 µm2). Further investigation of these leaf anatomy size theories in relation to athletic traffic tolerance should be conducted on additional cultivars.
Increased athletic field usage and a growing understanding of injury prevention have sports turf managers interested in implementing management practices that will improve turfgrass traffic stress tolerance. Previous research has shown that other abiotic stressors, such as mowing/rolling, high/low temperature, and drought, result in changes to turfgrass antioxidant enzyme activity levels. The study discussed in Chapter 3 was conducted to determine how simulated athletic traffic affects the magnitude and duration of changes in antioxidant enzyme activity of KBG. Two levels of simulated athletic traffic (0 and 2 games week-1) were applied to a blend of ‘True Blue HGT’ KBG using a modified Baldree traffic simulator for 7 simulated traffic events (STEs) in each year coinciding with the 2018 and 2019 fall football schedule. One STE of two games wk-1 represents a high school field hosting junior varsity and varsity games each week. Turfgrass leaves were individually cut from sub-plots at 0, 2, 4, 8, 12, and 24 h after simulated traffic application to assay the activities of ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD). Traffic application resulted in decreased activity of APX by 30-45% in 2019, CAT by 26-28% in 2019, and SOD by 3-13% on select rating dates in 2018 and 2019. Activity of APX was lowest at 4-12 h after STE. Catalase and SOD activity were highest at 0 or 4 h after STEs in early 2019 but in late 2019 activity was highest at 12 or 24 h after STEs. These results suggest that cumulative traffic stress increases the time required for antioxidant enzyme activity to return to baseline levels, directing future research to investigate timings and frequency of novel product application.
Soil degradation during construction is a widespread problem that results in soil loss through erosion and reduced vegetation establishment. Composted organic materials are used to restore soil health of compromised urban soils when planting trees and shrubs but less is known about compost amendments for turfgrass establishment. The experiments discussed in Chapter 4 was conducted to determine the effects of differing compost incorporation rates in two soil types on perennial ryegrass (Lolium perenne L.) establishment. A salt-sensitive and a salt-tolerant perennial ryegrass cultivar were seeded into a loam topsoil and a clay subsoil at soil:compost volume-by-weight ratios of 100:0, 80:20, 70:30, 60:40, 50:50, 40:60, and 0:100, using a mixed-source mature compost. Percent green cover and leachate pH, electrical conductivity (EC), and nitrate content were measured for the five-week establishment period. This trial showed that with a suitable topsoil, compost incorporation may not be necessary to obtain acceptable percent green cover but that small compost additions (30%) to a clay subsoil achieve faster establishment while limiting the potential for reduced plant health due to increased nitrate content or EC associated with higher levels of compost incorporation.
Benjamin W Pease
Pease, Benjamin W., "Traffic stress responses of Kentucky bluegrass and establishment of perennial ryegrass in compost amended soils" (2021). Graduate Theses and Dissertations. 18583.