ARS | Publication request: Surfactant Effects on the Water-stable Aggregation of Wettable Soils from the Continental U.S

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 2012
Publication Date: N/A

Interpretive Summary: Surfactants (wetting agents) may affect soil differently depending upon the ease with which a soil wets up (the soil’s wettability) or the water quality of rainfall or irrigation water. This laboratory study evaluated surfactant and water quality effects on water repellency and water-stable aggregation of wettable and nonwettable, agricultural soils collected from six states across the U.S. Two nonionic surfactants and a surfactant-free water control were first sprayed on air-dry soil. One and 72 hours thereafter, we determined the degree to which the soil resisted wetting, measured by timing the penetration of a water drop into the soil, termed the soil’s water drop penetration time, WDPT. Treated soil was then wetted more, then sieved for 10 min in water that contained either appreciable or few electrolytes, primarily calcium. The distribution of soil aggregates, naturally occurring clusters of sand, silt, and clay, that were stable after wet sieving was expressed as a mean weight diameter, MWD. Values of WDPT generally decreased slightly from 1 to 72 h after surfactants were applied. All in all, MWD values ranged from 0.11 to 1.43 mm but were little affected by surfactant treatment or water quality. This study’s findings, combined with those of a previous study, suggested that the type and amount of clay minerals in a soil affected its response to applied surfactants.

Technical Abstract: Surfactants may affect soil structure differently depending upon a soil’s wettability or the quality of rainfall or irrigation water. This study evaluated surfactant and water quality effects on water repellency and water-stable aggregation of wettable and nonwettable soils by quantifying water drop penetration time (WDPT) and mean weight diameter (MWD) for eleven agricultural soils from six states across the U.S. Two nonionic surfactants and a surfactant-free water control were sprayed (by misting) upon air-dry soil, then WDPT was measured one and 72 hours thereafter. Treated soil was slowly wetted with an aerosol to its water content at a matric potential of -3 kPa, then immediately sieved for 600 s in water that contained either appreciable or few electrolytes. Values of MWD ranged from 0.11 to 1.43 mm but were little affected by surfactant treatment or water quality as a main effect (p > 0.340). However, MWD was affected at p < 0.072 by a three-way interaction between soil, surfactant, and water quality, revealing that two coarse-textured soils responded differently to surfactants depending upon water quality. In summary, neither surfactants nor water quality affected the water-stable aggregation of most soils. Also, WDPTs generally decreased slightly from 1 to 72 h after surfactants were applied.