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
4University of Georgia-Tifton, and
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).
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
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).
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).
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
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.
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.
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.
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.
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.
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
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.
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
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
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.
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.
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.
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.
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.
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
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.
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
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,
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
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
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
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
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.
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
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
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