Morphologic and hydraulic properties of soils with water restrictive horizons in the Georgia Coastal Plain

Hydraulic and morphological properties of soils from a 0.36-ha site in the Georgia Coastal Plain were evaluated. Objectives included characterizing the morphological and hydraulic properties of major horizons in soils with plinthite, determining the extent of preferential flow, and relating flow/transport parameters derived from breakthrough curve analyses to morphological properties. These soils have developed from Miocene aged sediments and are classified in fine-loamy, siliceous, thermic families of Plinthaquic, Aquic, Arenic Plinthic, Plinthic, and Typic Kandiudults. Morphological evidence indicates that BC horizons are restrictive to vertical percolation of drainage water. Methylene blue dye staining, K sub(sat) and breakthrough curves (analyzed by two region/MIM using CXTFIT) were measured on 15-cm-diameter undisturbed cores to determine the effects of argillic horizons, argillic horizons with plinthite, and subjacent BC horizons on hydraulic properties of the soils. K sub(sat) for seven sampled pedons averaged 1.6 x 10 super(-2), 1.1. x 10 super(-2), and 3.8 x 10 super(-3) mm s super(-1) for Bt, Btv, and BC horizons, respectively. Dye staining and model output (MIM) indicate a greater degree of preferential flow with depth and subsequent less mobile area contributing to water flow. Analyses of the flowpaths indicate water is translocated in regions with relatively higher porosity that also contain a higher proportion of coarser pores. Micrographs indicate that flowpaths are associated with bio-pores and areas of better aggregation in the Bt horizons and structural voids in the BC horizons. BC horizons in these soils are less permeable because of increased clay content, differences in pore characteristics, and less cross-sectional area contributing to flow.