Preferential Flow and Pedotransfer Functions for Transport Properties in Sandy Kandiudults

Soils with differences in argillic and kandic horizon clay content (12–28% clay), thickness of overlying sandy eluvial horizons (ranging from <0.50 to >1.0 m), and degree of structural development occur in upland Kandiudult soils in the Upper Coastal Plain of Georgia. Interest in agricultural site-specific management necessitates more adequate characterization of solute transport properties between and within these soils. Undisturbed columns (15-cm diam., n = 34) were collected by horizon for three pedons typifying the extremes of the clay content in the argillic horizon. Breakthrough curves (BTCs) were conducted using a Br⁻ tracer and were evaluated by fitting the single- and two-region adaption of the convection–dispersion equation (CDE) to outflow measurements. Saturated hydraulic conductivity (K ₛ) measurements and methylene blue dye staining of conducting voids were also performed on the cores. Dye staining indicated differences in preferential flow occurred between surface (Ap), eluvial (E), and argillic and kandic (Bt) horizons. Retardation factors (R) were positively correlated with clay quantities, and horizons possessing relatively less clay (A and E horizons) possessed the highest α values (quickest solute exchange rates between mobile and immobile regions). Horizons with relatively higher clay quantities (Bts) had the lowest α and β (ratio of mobile water to the volumetric water content) values, but the highest effective dispersivity (λₑff) values. Dye-stained areas were correlated (r = 0.65) with β, which suggested β may be an approximation of the degree of preferential flow for these soils. For the three pedons studied, significant differences in α existed between the extremes, and thus they are interpreted to behave differently from a solute transport standpoint. Pedotransfer functions (PTFs) were developed for grossly estimating hydraulic and transport parameters.