Author
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Lehrsch, Gary |
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Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/20/2012 Publication Date: 6/4/2013 Citation: Lehrsch, G.A. 2013. Surfactant effects on the water-stable aggregation of wettable soils from the continental U.S. Hydrological Processes. 27:1739-1750. 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 the soil or the quality of rainfall or irrigation water. This study examined whether the water-stable aggregation of 11 wettable soils was affected by surfactants and the water in which the soils were sieved. The study also examined whether the wettable soils’ water drop penetration time (WDPT) was affected by surfactants, water drop quality, and elapsed time since the surfactants were applied. Two nonionic surfactants and a surfactant-free water control were sprayed (by misting) upon air-dry soil, then WDPT was measured 1 and 72 h thereafter. Subsequently, this 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. Water-stable aggregation, quantified as mean weight diameter (MWD), varied widely among soils, ranging from 0.10 to 1.36 mm. The MWDs were affected (at p = 0.06) by surfactant treatments, depending upon the soil but not sieving water quality. Surfactants affected the MWD of an Adkins loamy sand and Feltham sand, two of the three coarsest textured soils. Although WDPTs never exceeded 5 s, depending upon the soil WDPTs were affected by surfactant treatments but not by water drop quality. After surfactant application, WDPTs generally decreased with time for three soils but increased with time for one soil. Findings suggested that surfactants interacted (1) with clay mineralogy to affect MWD and (2) with soluble calcium to affect WDPT for certain soils. Surfactant treatments but not water quality affected bothMWDand WDPT for some but not all of 11 wettable, US soils. |
