SCSB# 395

MLRA 133A: Southern Coastal Plain
R.K. Hubbard1, D.E. Radcliffe2 ,  K. Cassel3, J. Hook4, and J. Dane5
1USDA-ARS Tifton, 2University of Georgia-Athens, 3North Carolina State University
4University of Georgia-Tifton, and 5Auburn University

Chapter Contents

Climatically the southern coastal plain (MLRA 133A) is humid subtropical and is contained within the subtropical oceanic margin (Atlantic and Gulf) (Trewartha, 1961). An abundant annual rainfall of 114 to 152 cm is concentrated in this area. The area has a biannual rainfall profile characterized by a primary maximum in summer (July to August) and a secondary maximum in the cooler months, which generally reaches a peak in March. Most of the abundant precipitation in the summer is from localized convective storms that are frequently accompanied by thunder and lightning. Mean rainfall (1922-1988) at the Coastal Plain Experiment Station, Tifton, Georgia, located within MLRA 133A is 120.8 cm (S.D. = 21.4 cm) (Sheridan and Knisel, 1989). Rainfall is lowest during the fall months. Annual water yields may range from 2.5 to nearly 76 cm, with an average of 36.5 cm (Sheridan and Mills, 1986). Annual water yield is the per unit area depth of accumulated streamflow that leaves an area over a one year period. Water yield during the first 20 weeks of the year accounts for 70 to 75% of the annual water yield (Sheridan et al., 1982). Baseflow or delayed subsurface flow resulting from highly permeable upland soils overlying relatively impermeable subsoil horizons accounts for 60 to 80% of the total annual streamflow is these areas of MLRA 133A (Knisel and Sheridan, 1983; Hubbard and Sheridan, 1983; Shirmohammadi et al., 1984).

The amount of rainfall and its temporal distribution in this region result in a high potential for solute movement to ground water. Supplementary irrigation, used on many soils in this region may also move solutes towards groundwater, particularly if excessive amounts of irrigation are applied.

Geology and Hydrogeology
The Atlantic and Gulf Coastal Plain containing MLRA 133A is a relatively low, flat region along the eastern and southern margins of the United States. The geologic deposits are seaward-dipping strata, chiefly unconsolidated materials, such as sand, clay, marl, and limestone, that resulted from fluvial and marine deposition, erosion and sedimentation, and the repeated advance and retreat of the seas. These materials, accumulated in relatively recent times (Quaternary, Tertiary, Cretaceous, and Jurassic), store an enormous amount of water (LeGrand, 1962).

The geologic structure of the Coastal Plain, that is, the alternate layering of permeable and impermeable materials, together with the slight homoclinal dip, is suited ideally to the occurrence of artesian water (LeGrand, 1962). The regional artesian aquifer system of MLRA 133A is unusual in both thickness and areal extent. Covering about two-thirds of the southeastern Coastal Plain, it is one of the largest groundwater sources in the United States (Stringfield, 1966).

The regional aquifer system generally consists of two major water-bearing units: the surficial aquifer and the regional artesian aquifer system (Miller, 1986). The surficial aquifer typically is underlain by a thick sequence of fine, clastic, and relatively impermeable carbonate materials of the middle Miocene Hawthorn Formation; when present, these materials form the upper confining unit for the regional artesian aquifer system (Miller, 1986; Thomson and Carter, 1963). While the Hawthorn generally is considered an aquiclude because of the presence of clays and sandy clays, in some places moderately permeable sandbeds occurring within the Hawthorn are capable of providing water (LeGrand, 1962). The high degree of variability in the lithology and thickness of the Hawthorn results in variability in the rate of vertical movement of water from the surficial aquifer to the regional artesian aquifer system (Miller, 1986). However, even where portions of the Hawthorn are somewhat permeable, the permeability is much less than in the underlying aquifers.

Sinkhole or karst topography has formed in areas of MLRA 133A where limestone aquifers are at or near the surface and where the Hawthorn is absent, thin, or removed by erosion. The regional artesian aquifer has cavities and solution channels that are probably comparable in size and extent to those in Mammoth Cave, Kentucky (Stringfield, 1966).

Recharge by Infiltration and Percolation
Recharge of the regional aquifer system occurs in several ways. Rainfall, storm runoff, and streamflow all may contribute to recharge in the limestone outcrop areas, also referred to as primary recharge areas (Krause, 1979). The amount of actual recharge, however, may be small compared to the potential available recharge, because the potential recharge rate generally exceeds the rate at which aquifers can accept and transmit water (LeGrand, 1962).

Infiltrating water percolates toward the water table and then moves either laterally toward surface streams or to recharge the local or regional aquifer. The rate of water movement depends upon the properties of the surface soil and the presence and characteristics of confining beds. Infiltration rates generally are high because a majority of surface soils in MLRA 133A are sandy (Fiskell and Perkins, 1970). In confined areas, however, deep percolation of excess water through permeable surface soils is impeded by low-permeability materials, including plinthite and upper portions of the Hawthorn Formation, at shallow depths 0.9 to 3.0 m(3 to 10 feet). A vertical hydraulic conductivity of 0.4 m per year (1.2 feet per year) was reported for the shallow impeding layer underlying a Coastal Plain soil in the Tifton Upland near Tifton, Georgia (Rawls and Asmussen, 1973). This value compares closely with the equivalent range of vertical conductivities of 1.7 to 0.001 m per year (5.5 to 0.003 feet per year) reported for the Hawthorn Formation (Miller, 1986).

Recharge via Solution Features
Recharge to the regional aquifer system also may occur where the limestone is at or near the surface or where the upper confining unit is thin, absent, or removed by erosion and subsequently penetrated by sinkholes and other solution features (Krause, 1979; Stringfield, 1966). Water from ponds, rivers, or lakes may recharge the regional aquifer system through open sinks and man-made or naturally occurring wells that drain low-lying, wet areas directly into underlying aquifers (Stringfield, 1966). The upper confining unit may be breached locally by sinkholes and other openings that connect the regional aquifer system directly with the surface (Miller, 1986). This semi-confined condition generally occurs where the Hawthorn is less than 100 feet thick and more sandy in texture. However, sinkholes or vertical solution shafts may extend from the surface through as much as several hundred feet of the Hawthorn. At least one sinkhole reportedly was nearly 500 feet deep (Stringfield, 1966).

Substantial rates of direct recharge (maximum rate of 8.5 cubic meters [300 cubic feet] per second) with a mean annual rate of 3.2 cubic meters (112 cubic feet) per second reportedly were flowing directly from the Withlacoochee River into the regional aquifer system in the karst region of southern Georgia (Krause, 1979). Substantial amounts of direct recharge also have been reported entering the aquifer through drainage wells in the Valdosta, Georgia area (Stringfield, 1966). Evidence of these sources of direct recharge has been shown by local anomalies in potentiometric surface maps. The area of influence of these inputs has been estimated to be about 5,000 square miles (Stringfield, 1966). Although recharge by surface water is beneficial from a water quantity standpoint, recharge may not be within water quality standards for drinking water (Federal Register, 1975; Krause, 1979).

In MLRA 133A, many sinks and solution features (channels or cavities) filled with relatively permeable, unconsolidated sediments during advances of the seas. Such areas provide relatively permeable routes for water movement into the regional aquifer system (Stringfield, 1966). Lakes occupy many of these areas in the “lakes region” of Florida and Georgia. Rates of downward leakage have been estimated at two to three inches per month for one such lake (Stringfield, 1966). Regions of northeast Florida and southeast Georgia, where the Hawthorn is as much as 538 feet thick, generally do not show sinkhole development, and localized recharge via sinkholes is not typical of these areas (Stringfield, 1966).

Fig. 1. STATSGO soils of the Southern Coastal Plain in MLRA 133A.

Landscape and Soils
MLRA133A can be described topographically as an area of floodplains, river terraces, and gently sloping uplands. Interstream divides are moderately wide and separate relatively broad valleys (Jensen et al. 1959). The area contains a range of soils depending on original parent material and topography. The climate, vegetation, and length of time for soil formation were similar throughout MLRA 133A; hence, the dominant soil-forming factors for the area were parent material and landscape position. STATSGO soils are depicted in Fig. 1.

Soils of MLRA 133A are primarily Udults, that is, these soils are well or moderately well drained, low in bases, have silicate accumulation in B horizons, and have formed in a humid climate. As Ultisols, they are highly weathered, with kaolinite as the dominant clay mineral. Soils in the region can be grouped as upland or lowland, with lowland soils being those immediately adjacent to drainage networks. Most upland soils are classified as fine-loamy or loamy, siliceous, thermic Arenic, Typic, or Plinthic Paleudults or Kandiudults (Calhoun, 1983; Soil Survey Staff, 1987). Bottomland soils adjacent to drainage networks are primarily loamy, siliceous, thermic Arenic, and/or Plinthic Paleaquults with some Fluvaquents and Psammaquents (Calhoun, 1983). Upland soils generally are well drained, whereas bottomland soils are poorly to very poorly drained, with water frequently standing on the surface. The upland soils may range in texture from sand to clay loam at the soil surface. Landuse is primarily agricultural with cropland, forest, and pasture occupying large areas. Swamp hardwood communities occur along stream edges and are often accompanied by thick undergrowth vegetation.

Upland soils of the Georgia Coastal Plain have surface horizons that are primarily sands, loamy sands, or sandy loams. The infiltration rates for these soils generally are in excess of 5 cm h-1 (Rawls et al., 1976). At depth, however, many of these soils contain horizons that impede downward percolation of water. Plinthic soils of the Georgia Coastal Plain contain such horizons at depths ranging from 75 to 200 cm below the soil surface (Perkins et al., 1978; 1979). The combination of sandy surface textures and relatively impermeable subsoils causes up to 79% of total runoff to leave the upland landscape as shallow subsurface flow (Hubbard and Sheridan 1983).

Soil Series

Alapaha Series
The Alapaha series is a member of the loamy, siliceous, thermic family of the Arenic Plinthic Paleaquults, according to U.S. taxonomy (Perkins et al., 1986). The Alapaha series consists of deeply weathered, poorly drained soils with moderately slow permeability. These soils are developed in sandy to loamy sediments along small drainage ways and in flat depressions.

Alapaha soils, even with artificial drainage, have poor potential for row crops, forages, or pastures. The high aluminum content and dense plinthic layer limit root penetration. These soils offer severe restrictions for waste disposal sites, building site development, and most recreational development.

Carnegie Series
The Carnegie series is a member of the clayey, kaolinitic thermic family of the Plinthic Paleudults in the U.S. soil taxonomic system (Perkins et al., 1986). The Carnegie series consists of deep, well drained soils of moderately slow permeability and medium to rapid runoff. These soils occur on short side slopes and knolls formed on geological erosional surfaces within broad interstream divides. They are formed in thick reticulately mottled sediments of marine origin.

Carnegie soils have moderate to good potential for growing most cultivated crops, pastures, and forages. Carnegie soils have moderate to severe limitations for sanitary facilities and moderate limitations for recreation because of a relatively high clay content and slow percolation. The potential for residential development and roads is good to fair depending on slope.

Clarendon Series
The Clarendon series is a member of the fine-loamy, siliceous, thermic family of the Plinthaquic Paleudults according to U.S. soil taxonomy (Perkins et al., 1986). Clarendon soils are moderately well drained and are moderately permeable in the upper part of the argillic but slowly permeable in the lower part. They occur on nearly level, broad interstream divides in the coastal plain and are formed in loamy marine sediments.

A perched water table is usually found during periods of extended rainfall, especially during winter and early spring. The perched water table is usually within 63 to 90 cm of the surface in later winter and/or early spring, and is due primarily to plinthite. Clarendon soils have low potential for any use when a seasonally high water table would offer restrictions. The low strength of Clarendon soils imposes moderate to severe restrictions for buildings, roads and streets, and fill material.

Dothan Series
The Dothan series is a member of the fine-loamy, siliceous, thermic family of the Plinthic Paleudults according to U.S. soil taxonomy (Perkins et al., 1986). Dothan soils have deep, well-drained pedons with moderate permeability in the upper part of the subsoil and moderately slow permeability in the lower part. These soils formed in loamy marine sediments and occur on nearly level to broad interstream areas.

Duplin Series
The Duplin series is a member of the clayey, kaolinitic thermic family of Aquic Paleudults (Perkins et al., 1978). Duplin soils have moderately well drained pedons but show evidence of a perched water table within 75 cm of the surface. They generally occur on nearly level (0 to 2% slopes) areas near the base of gently sloping Coastal Plain soils. The Duplin series has good potential for most cultivated crops and pasture grasses commonly grown in the area. The soil has good potential for woodland, but equipment limitations and seedling mortality are problems related to the wetness factor. Wetness and slow percolation cause this soil to have a fair to poor potential for most non-agricultural uses except for sewage lagoon and pond reservoir areas.

Faceville Series
The Faceville series is a member of the clayey, kaolinitic thermic family of the Typic Paleudults (Perkins et al., 1978). Soils of this series are deep, well drained and moderately permeable. They occur on nearly level to gently sloping smooth to convex uplands. Soils of the Faceville series are among the most productive soils of the Coastal Plain Province. They are well adapted for row crops, small grains, pastures, and woodlands. These soils have few restrictions (except slope) and have good potential for most agricultural and non-agricultural uses.

Fuquay Series
The Fuquay series is a member of the loamy, siliceous, thermic family of the Arenic Plinthic Paleudults (Perkins et al., 1986). The Fuquay series consists of deep, well drained soils that have moderate permeability in the upper part of the argillic horizon and slow permeability in the lower part. These soils are developed in sandy to loamy marine sediments on broad upland ridge tops of the southern coastal plain.

Although Fuquay has good tilth and a deep root zone (up to 1.2 m [3.9 feet]), soils of this series offer only fair to moderate potential for row crops, small grain, hay, and pasture grasses. This is due primarily to the thick sandy surface that has a low water-holding capacity. Potential is fair to good for southern pine species. Fuquay soils have good potential for community development and sanitary facilities. Percolation is rapid to depths up to 120 cm (Perkins et al., 1979). The sandy nature of the soil surface (loamy sand and coarser) results in moderate restrictions for recreation.

Greenville Series
The Greenville series is a member of the clayey, kaolinitic, thermic family of the Rhodic Paleudults (Perkins et al., 1978). The Greenville soils are well drained and occur on nearly level to gently sloping smooth to convex interstream areas. They are derived from residuum of interbedded marine sediments from Eocene and Oligocene geologic formations.

Soils of the Greenville series are well adapted for crop land and pasture land. These soils also have a high potential for woodland use. Greenville has a low to moderate swell-shrink potential that is characteristic of soils with kaolinite as the dominant clay mineral. These soils have good potentials for surface and subsurface waste disposal, buildings and roads, pond reservoir areas, and recreation but only fair potential for topsoil and roadfill material.

Henderson Series
The Henderson series is a member of the clayey, kaolinitic, thermic family of the Typic Paleudults (Perkins et al., 1978). Soils of this series are well drained but slowly permeable and clayey. They occur on gently sloping to moderately steep slopes and are derived from clayey acid residuum from impure limestone containing chert. The Henderson soils have poor potential for row crops and medium potential for pasture. Restrictions are due to slope, cherty surface, and slow permeability. The soil has good potential for pine plantations and offers no significant management problems for woodland use.

Leefield Series
The Leefield series is a member of the loamy, siliceous, thermic family of the Arenic Plinthaquic Paleudults in the U.S. soil taxonomic system (Perkins et al., 1986). The Leefield series consists of deep, somewhat poorly drained, moderately permeable soils with slow runoff. A perched water table at depths of 50 to 75 cm is present about four months each year. These soils occur on nearly level uplands of the southern coastal plain. Leefield soils developed in sandy and loamy sediments of the Neogene undifferentiated deposits.

Leefield soils may have wetness as a limiting factor. Even so, where adequately drained these soils have moderate potential for row crop, forage, and pasture production. In view of the thick sandy surface, supplemental irrigation and adequate soil amendments are usually necessary during the warm season to achieve desired crop yields. Soils of this series have fair to good potential for southern pines. The wetness factor and a thick sandy surface impose moderate to severe restrictions for community and recreation development and sanitary facilities.

Norfolk Series
The Norfolk series is a member of the fine-loamy, siliceous, thermic family of the Typic Kandiudults (Perkins et al., 1986). Norfolk soils are well drained, moderately permeable soils that occur on uplands with slopes ranging from 0 to 10%.

Norfolk soils are well suited for many uses and are intensively used for growing corn, soybeans, small grains, tobacco, cotton, and truck crops. The soils are also suitable for hay and pasture, woodlands, and most urban and recreational uses. Soil erosion may be a problem on the steeper slopes. Wetness may be a problem in some areas which would place limitations on sites for buildings requiring basements or septic tanks.

Pelham Series
The Pelham series is a member of the loamy, siliceous, thermic Arenic Paleaquults according to U.S. soil taxonomy. Soils of this series consist of deep, poorly drained, moderately permeable soils with a water table usually at 30 to 90 cm below the surface during late winter and early spring when evapotranspiration is relatively low. Pelham soils are being formed in sandy and loamy sediments of marine origin. They occur on broad, nearly flat, upland depressions and near drainage ways in the Atlantic Coast Flatwoods and Southern Coastal Plain Soil Provinces.

Without artificial drainage Pelham soils have a water table within one meter of the soil surface much of the year. High sand and low clay content facilitates rapid decomposition following drainage and results in low water-holding capacity and cation exchange capacity (CEC) as reported in Tables 10 and 11. When adequately drained, Pelham soils have moderate crop yield potential but usually have low soil fertility. Perkins et al. (1984) reported potential yield for corn and soybeans of 150 and 40 bushels per acre, respectively, for this series. Pelham soils have moderate potential for horticultural crops such as blueberries grown under intensive management. These soils have severe restrictions for community development, waste disposal sites, and most recreational development.

Riverview Series
The Riverview series is a member of the fine-loamy, mixed, thermic family of Fluventic Dystrochrepts (Perkins et al., 1978). Soils of this series consist of well drained, nearly level soils along small drainage ways and in slight depressions. They are formed in local alluvium washed from Greenville, Faceville and Tifton soils on nearby slopes. Riverview soils are well suited for row crops, forages, and woodlands. Since soils of this series are subject to flooding during periods of excessive rainfall they have a low potential for most nonagricultural uses. Although the swell-shrink potential is low, Riverview soils have moderate restrictions for pond reservoirs and pond embankments due to seepage and poor resistance to piping and erosion.

Tifton Series
The Tifton series is a member of the fine-loamy, siliceous, thermic family of the Plinthic Paleudults in the U.S. soil taxonomic system (Perkins et al., 1978; 1986). This series consists of deep, well drained, moderately permeable soils that occur on gently sloping to rolling interstream uplands in the southern coastal plain soil province. Tifton soils are developing in loamy sediments of marine origin. Two characteristic features of the Tifton series are the presence of more than 5% ironstone nodules in the upper part of the pedon and more than 5% plinthite in some horizon in the lower part of the pedon. In most years, a perched water table is found in or above the plinthic layer during late winter and/or early spring when evapotranspiration is low.

Tifton soils are highly productive. They have high potential for the growth of row crops, forages, pastures, and woodland. Soils of the Tifton series have good potential for most landuses except subsurface waste disposal and uses of soils requiring great strength. A genetic pan that occurs in association with plinthite restricts water movement during periods of excess soil water. This pan imposes moderate restrictions on the use of the soil for septic tank filter fields. Low strength creates moderate restrictions on the use of Tifton soils for community development.

Troup Series
The Troup series is a member of the loamy, siliceous, thermic Grossarenic Paleudults according to U.S. soil taxonomy (Perkins et al., 1986). The Troup series consists of deep, well drained, moderately permeable soils with thick sandy surface layers and loamy subsoils. Troup soils occur on nearly level ridge tops to rolling coastal plains uplands. They are developed in unconsolidated marine and/or fluvial deposits of sandy and/or loamy sediments.

The soils of the Troup series have only fair potential for row crop, forage, hay, and pasture because of a sandy surface between 1 and 1.5 m in thickness. Although the clay content of the Troup series is quite low, its composition is similar to other soils with which it is associated. These soils respond well to irrigation, fertigation, and good management, however. The sandy nature of the soil creates moderate hazards in management of southern pine species. Troup soils have slight to moderate restrictions for community development, building sites, and recreational development. They have moderate to severe restrictions for sanitary and waste disposal facilities because of excessive drainage and seepage.

Wagram Series
The Wagram series is a member of the loamy, siliceous, thermic family of Arenic Kanhapludults. The soil that developed from loamy Coastal Plain sediments is similar to Norfolk but the argillic horizon begins at depths deeper than 50 cm below the soil surface. Wagram is found on side slopes and broad, flat interstream divides in the uplands. The Wagram series is deep, moderately well to excessively drained, and moderately permeable. Infiltration rate is medium to high and surface runoff is low. The water table remains below the solum.

Natural fertility of the soils that developed under forest vegetation is low. Wagram soils are suited for cultivated cropland such as corn, soybeans, tobacco, and small grains. These soils tend to be droughty due to low water holding capacity. Being very sandy in the A and E horizons, these soils can be tilled under a wide range of soil water content conditions, but the soil often compacts severely when tilled in a wet condition. Conservation tillage and crop residue management are helpful to conserve water for cropped fields.

Soils Information
Descriptions of soil profiles for soils of MLRA 133A are contained within county soil maps within the states of the southeast region. More technical information is available where specific studies have included characterization of soil physical properties. Such studies have been conducted at a number of different sites.

A soil characterization study was conducted at Tifton, Georgia in the early 1980s. Three different soil series (Tifton, Dothan, and Fuquay) were characterized using two pits for each soil type. One site was forested and the other site was agricultural for each of the three soil series. The information collected included both soil chemical and soil physical properties. This information was reported in the bulletin entitled “Characteristics of selected upland soils of the Georgia Coastal Plain,” ARS-37, by R.K. Hubbard, C.R. Berdanier, H.F. Perkins, and R.A. Leonard. Soil profile descriptions for Dothan are contained in Table 1, those for Fuquay in are in Table 2, and those for Tifton are in Table 3. Tables 4, 5, 6, 7, 8, and 9 contain the physical properties of these soils.

Characterization of a Tifton soil was made during a 1992-93 study. The experiment site was on the Abraham Baldwin Agricultural College research farm in Tifton, Georgia (30° 29' N latitude and 83°32' longitude). In 1992 and 1993, two plots, A and B, were constructed in a field to be planted to corn. Each plot had dimensions of 14.5 m (eight 1.5-m wide beds of two rows of corn each) by 42.9 m with rows parallel to the 3% slope. Plots were separated from each other and from outside areas by 18 m with soil preparation and corn managed as within the plots. The soil was a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) which is generally rated moderately-well drained (Perkins et al., 1986). Surface crusts can form on this soil when exposed to high rainfall intensity (Radcliffe et al., 1991; Chiang et al., 1993). Transient perched water conditions can occur at the Ap-Bt1 interface (about 0.3 m below the soil surface), and at the Btv-C interface (at 1.0 to 1.3 m). The latter is due to a thick and very low permeability sandy clay or sandy clay loam material of geologic origin.

Field operations on the plots included (1) disk harrowing twice at a depth of 0.15 m; (2) moldboard plowing to a 0.3 m depth and subsequent shaping of the seedbed with a light harrow; (3) broadcasting granular fertilizer; (4) rototilling to a 0.12-m depth incorporating a nematicide; (5) planting corn in rows 0.91 m apart; (6) broadcast spraying of alachlor and atrazine herbicides; (7) applying nitrogen (N) as liquid urea-ammonium nitrate in bands near the rows; and (8) spraying with foliar fungicide and insecticide when corn was 0.1,0.3, and 1.2 m tall. After shaping of the seedbeds, hydrological instrumentation was installed to measure and collected runoff.

Soil probes were made to a depth of 1.5 m from 24 sites along the perimeter of plots A and B, typical horizon boundaries were identified, and undisturbed cores from within those horizons were sampled. Saturated hydraulic conductivity was measured on those cores by the constant head method of Klute and Dirksen (1986), with the modifications suggested by Hill and King (1982). Soil water retention characteristics were measured at 0.5, 1.0,2.2, 4.8, 9.8, 21.8, 45.6, and 100 kPa suctions using undisturbed soil cores. Particle size distribution of air-dried soil was determined by the hydrometer method (Day, 1965), and water retention in loose soil at 33 kPa (q33 ) and 1500 kPa (q1500 ) were obtained using Richard’s method (Richards, 1965). Organic carbon content was determined by the modified Walkley-Black method (Nelson and Sommers, 1982) in a separate characterization of soil at this farm (Perkins et al., 1986). These measured values are summarized in Table 10 and Table 11.

Transport properties for three different types of horizons (argillic-Bt, argillic containing plinthite-Btv, and BC horizons) were analyzed on undisturbed cores (15-cm diameter) from a 0.36 ha plot located in the Middle Georgia Coastal Plain, near Tifton, Georgia (Shaw et al., 1997). Eighteen pedons in this plot were classified in fine-loamy, siliceous, thermic families of Plinthaquic, Aquic, Plinthic, and Typic Kandiudults. All soils in this study contained some plinthite (representative soil description given in Table 12), and reticulately mottled BC horizons (from 89- to 175-cm depth) which were slightly denser and had more clay than overlying argillic horizons. Studies have show that in landscapes with similar soils, the amount and shape of plinthite, and the presence of these BC horizons can have a significant effect on hydraulic properties (Blume et al., 1987; Carlan et al., 1985).

Saturated hydraulic conductivities (Ks ) for seven sampled pedons decreased from Bt (3.2 x 10-2 mm s-1 ) through Btv (1.7 x 10-2 mm s-1 ) and down to BC horizons (5.2 x 10-3 mm s-1 ) (Table 13). CXTFIT was used to determine transport parameters from Br breakthrough curves. Dispersivities between the three horizons did not differ greatly and were considered slightly high for column scale (percent ranged from 4.1 to 5.9 cm). Mobile water fraction (qm/q) decreased with depth from 0.72 in the Bt to 0.19 in the BC horizon. This correlated with methylene blue dyed areas that decreased from 64.5 (Bt), to 45.6 (Btv) to 17.5% (BC). Analyses of porosity in these cores (using image analyses techniques) indicated that porosity was significantly greater (P=0.5) in dyed areas than in undyed areas, and dyed areas contained larger pores. In addition, the shallower Bt horizons contained larger pores, and micromorphological analyses indicated a significant biological component to flowpaths in the argillic horizons. This could contribute to higher Ks in Bt horizons.

Hydrological Parameters on Two Upper Coastal Plain Soils
In a recent study (Vervoort, 1997), two soil series in Ft. Valley, Georgia were sampled to determine their hydrological characteristics. The soil series, Esto and Faceville, are both clayey, kaolinitic, thermic Typic, Kandiudults. The morphological descriptions are given in Tables 14 and 15. Three, 15-cm diameter, 30 cm long columns were carved out of four horizons in the Esto (Ap1, Bt2, Bt3, and BC1) and three horizons in the Faceville (Ap1, Bt2 and BC1). The columns carved out of the Ap1 horizon for both pedons included, due to their length, the Ap2 and a small portion of the Bt1 horizon. Saturated hydraulic conductivity (Ks) was measured on ten separate small cores (7.5 cm diameter, 6 cm length). A breakthrough curve (BTC) was performed on the intact columns using Br or Cl. Transport parameters for the convection dispersion equation (CDE) and the mobile immobile model (MIM) were developed using CXTFIT (Parker and van Genuchten, 1984). Finally the intact columns were leached with blue dye and sectioned to determine the percent dyed area. Retardation coefficients (R) for Br were developed separately on small columns with packed soil. These results are summarized in Tables 16 and 17.

The Esto pedon had a wetter moisture regime and developed a more expressed and finer structure in the subsoil than the Faceville. Both soils exhibited an increase in structure expression with depth. Water retention parameters based on the Mualem-van Genuchten equation between the pedons were similar. The data in general indicated that morphologically observed structure highly influenced the variability in Ks and water retention data in the lower horizons of both pedons. Well-expressed structure was indicated by high CV of the small core Ks data. Air-entry values were well correlated to Ks . Break-through curves and blue dye patterns indicated increasing non-equilibrium flow with depth in the subsoil of both pedons. Dispersivities from the CDE were greater than the column length in the Esto Bt3 and BC1 horizons of both pedons, indicating preferential flow in these horizons. This was confirmed by the low blue dye staining in these horizons. Both CDE and the eff (calculated from the three MIM parameters) were well correlated (r2 = 0.69) to the average blue dyed area in the columns, indicating that the parameters in the CDE and the MIM represent true physical properties. Exchange coefficients (a*) decreased with depth and were correlated to clay content and weakly correlated to average blue dyed area. Both correlations confirm the relationship between a* and ped size. Dispersivities were well correlated (r2 = 0.78) to the CV of the Ks and the slope of the water retention curve. Well expressed structure was indicated by high dispersivities and low qm/q and a*

Anderson and Cassel (1984) conducted studies on Norfolk soils. Tillage pans are common in Norfolk soils. Furthermore, the strength of the pan varies with the shape and distribution of sand particles in those horizons (Cruse et al., 1981). Work by Anderson and Cassel (1984) showed that the depth, thickness, and hardness of the E horizon and lower portion of the Ap horizon are affected by minor changes in elevation. Using a modified regular grid system a 1.4 ha field was sampled at 130 locations. Data in Table 18 show that the thickest E horizon occurs at the intermediate elevation. Water retention at -10 and -33 kPa also varies with landscape position, but the -1500 kPa value is affected very little. These variations in water retention influence solute transport through the soil; soils with low water retention capacity will have larger leaching losses. Soil physical property data for a tilled Wagram soil at Clayton, North Carolina, are given in Table 19. Bulk densities of the A and E horizons commonly exceed 1.6 g cm-3 reflecting the very weak soil structure and susceptibility of this soil to compaction and tillage pan formation. The plant available water holding capacity is low in the A and E horizons; this low water retention exacerbates nutrient leaching. Mathematical expressions for in situ unsaturated hydraulic conductivity as a function of volumetric water content for the various depths of the soil in Table 19 are given in Table 20. The field-measured hydraulic conductivity data were collected using the instantaneous profile method (Cassel, 1985). Additional data for the Wagram and Norfolk series are given in Quisenberry et al. (1987).

Literature Cited
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