Alkyl-Capped Block Copolymer Surfactants for Remediation of Soil Water Repellency and Heterogeneous Rootzone Moisture

Soil water repellency (SWR) leads to nonwettable soils, heterogeneous rootzone moisture, reduced irrigation efficiency, leaching due to preferential flow, localized dry spots, and deterioration of turfgrass quality. Nonionic hydroxyl-terminated methyl oxirane-oxirane (EO/PO triblock copolymers) copolymers are commonly employed to remediate SWR. To determine if molecular modification influenced remediation performance, C1–C4 alkyl ethers of methyl oxirane-oxirane copolymers were produced through etherification of hydroxyl-terminated methyl oxirane-oxirane copolymers. ACA 1820, an alkyl ether of methyl oxirane-oxirane copolymer (MW approximately 2500) (applied monthly at 1.9 kg ha−1) reduced SWR and maintained quality at higher levels (p=0.05) for longer periods than the hydroxyl-terminated methyl oxirane-oxirane copolymer or the control. Turf density in plots treated with the alkyl ether of methyl oxirane-oxirane copolymer was three-fold greater than the control and two-fold greater than in plots treated with the hydroxyl-terminated methyl oxirane-oxirane copolymer. Rootzone moisture was more homogeneous in plots treated with ACA1820 than other treatments. Differences in visual turf quality were observed for up to nine months after the last application of the alkyl ether of methyl oxirane-oxirane copolymer. The observed effects are proposed to be due to interfacial interactions of the alkyl caps both in solution and at hydrophobic soil surfaces.