Examining the Structure-Function Relationship of Block Copolymer Soil Surfactants in Sand-Based Putting Greens

Soil surfactants are important for water management on golf courses, particularly sand-based putting greens. However, understanding functional differences among products is challenging for many practitioners. Product transparency is lacking, creating a need to evaluate turfgrass soil surfactants on an active-ingredient basis. For amenity turfgrass, nonionic block copolymers (poloxamers) are the largest and most widely used soil-surfactant chemical category. The objective of this research was to compare individual poloxamers for their effectiveness as stand-alone soil surfactants based on soil volumetric water content (VWC) and turfgrass quality. A 2-year study was conducted on a sand-based creeping bentgrass (Agrostis stolonifera L.) putting green. The study used a two-factor split-plot design arranged as a randomized complete block with four replications. Irrigation was the whole-plot factor, with two levels: 60% and 80% evapotranspiration replacement. Six soil-surfactant treatments were applied to individual split plots and included four structurally related poloxamers (181, 182, 184, and 188), an untreated control (UC), and a commercial standard (CS) (an alkyl-terminated block copolymer). Poloxamers all had the same molecular-weight hydrophobe, but each contained a different hydrophile percentage. Surfactants were applied every 28 days and immediately irrigated with 5 mm water. VWC was measured across 3.8 and 7.6 cm using time-domain reflectometry. Turfgrass quality was assessed visually (on a scale from 1 to 9) and through digital-image analysis. Results indicated that above-ground turfgrass quality did not necessarily reflect below-ground VWC. Across variable weather conditions, Poloxamers 181 and 182, which had the lowest hydrophile percentages, were not significantly different from the CS, whereas Poloxamer 188, which had the highest hydrophile percentage, was not significantly different from the UC. These results indicated that longer hydrophile chains may reduce the perceived effectiveness of turfgrass soil surfactants in sand-based putting greens. Results also demonstrated the need to further explore the structure-function relationships of turfgrass soil-surfactants.