Surfactant Effects on the Water–Stable Aggregation of Wettable and Nonwettable Soils.

Surfactants may affect soil structure differently, depending upon a soil’s wettability or the quality of rainfall or irrigation water.  This study evaluated the effects of two nonionic surfactants and a surfactant-free water control on the water drop penetration time (WDPT) and mean weight diameter (MWD) of water-stable aggregates in eleven agricultural soils from six states across the U.S.  I measured a) WDPT to quantify soil wettability, and b) MWD to indicate soil structural change.  Each of the three surfactant treatments was 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.  Resulting values of MWD ranged from 0.10 to 1.43 mm but were little affected by either surfactant treatment or water quality as a main effect (P > 0.340).  However, I did detect evidence at P < 0.072 that MWD was affected by a three-way interaction between soil, surfactant, and water quality, revealing that coarse-textured soils responded differently to surfactants, depending upon water quality.  Measured MWD values varied greatly from soil to soil, largely due to differences in texture and organic C content.