Date of Graduation

5-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Agricultural, Food and Life Sciences (PhD)

Degree Level

Graduate

Department

Horticulture

Advisor/Mentor

Michael Richardson

Committee Member

Stanley Kostka

Second Committee Member

Douglas Karcher

Keywords

golf course; hydrophobicity; putting green; Soil surfactant; Turfgrass; Wetting agent

Abstract

Soil surfactants, commonly referred to as wetting agents, are a leading water management strategy for golf courses. Non-ionic block copolymers are the most common type of turfgrass soil surfactant. However, differences in the registration process and labeling requirements allow soil surfactants to enter the marketplace accompanied by far-less data compared to other products used on golf courses. This has led to considerable confusion among golf course superintendents. Three primary sources of confusion are: (i) the widely-used marketing terminology of “penetrants” and “retainers” to classify wetting agents; (ii) active ingredients which in some cases are not disclosed at all; and (iii) multiple application rates and intervals given on product labels. Therefore, three separate field research experiments were conducted with objectives to (i) compare the penetrant and retainer products from four different manufacturers (Aquatrols, Precision Laboratories, Floratine, and Harrell’s) for their ability to move/hold water at different depths within putting green rootzones; (ii) evaluate soil surfactants at the active ingredient level, working with four structurally related block copolymer compounds (Poloxamers 181, 182, 184, 188) all with the same molecular-weight central hydrophobe, and each with a different percentage of terminal hydrophile; and (iii) compare five different application rates and intervals that included: two season-long applications at standard and high rates, two recurring monthly applications at standard and reduced rates, and a recurring application every two months. All experiments included non-treated controls (NTC). Data collection included (i) estimating volumetric water content (VWC) using portable moisture meters at multiple depths in the rootzone; above-ground assessments using (ii) digital image analysis to determine percent green turfgrass cover, color, and turfgrass quality, and (iii) visual ratings for turfgrass quality and localized dry spot (LDS) development. Between 2018 and 2023, studies were conducted primarily in Fayetteville, AR on sand-based putting greens of both creeping bentgrass (Agrostis stolonifera, L.) and ultradwarf bermudagrass (Cynodon dactylon (L.) Pers x Cynodon transvaalensis Burt-Davy). In the first study, penetrant and retainer terminology was problematic because of, (i) lack of significant differences between penetrants and retainers, (ii) significant differences between soil surfactants within the same category, (iii) inconsistent abilities of both penetrants and retainers to predictably affect VWC relative to NTC, and (iv) variability in the performance of penetrants and retainers from manufacturer to manufacturer. In study two, Poloxamers 181 and 182, with the lowest HLB values of 3 and 7, respectively, consistently performed similar to a commercial turfgrass wetting agent, whereas Poloxamer 188, with the highest HLB value (29), resulted in lower turfgrass quality and lower average VWC, along with a greater incidence of LDS. Study three observed the potential for cost savings through reduced soil surfactant rates and extended intervals, as well as a three week lag-time between significant VWC differences below-ground in the rootzone and significant above-ground differences in LDS; a strong influence of weather, especially rainfall, on soil surfactant performance; and an ability to assess moisture uniformity through standard deviation of VWC. Future turfgrass soil surfactant research should include investigations into hydrophobicity development at the root-soil interface (rhizosphere).

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