MLRA 137: Carolina and Georgia Sand Hills
North Carolina State University
Major land resource area (MLRA 137) occupies a relatively small
area of land compared to most of the other MLRAs and is occupied primarily
by deep sandy soils that are droughty and difficult to manage intensely.
As we will see, these soils have low water holding capacities and are subject
to leaching losses.
Location and Landuse
MLRA 137 is composed of land in a relatively narrow strip extending
east northeast from the western boundary of Georgia across the entire state
of Georgia, across the entire state of South Carolina, and about halfway
across North Carolina (view of regional map). This
strip of land separates MLRA 136, the Southern Piedmont, to the west, from
MLRA 133A, the Southern Coastal Plains, to the east. Soils from both the
Piedmont and Coastal Plain are found in MLRA 137. Much of the general information
to follow was extracted from USDA (1981).
MLRA 137 occupies an area of 22,680,000 ha (55,606,400 acres). The strip
of land is about 650 km (404 miles) long and varies in width from 6 to
80 km (4 to 50 miles), but is mostly less than 40 km wide. Natural vegetation
is/was pine-oak with long leaf pine being the dominant species. Currently
most of the land is under forest cover (Table
1) with pine and scrub oak being dominant. Pulpwood and lumber are
the primary forest products. Turkey, blackjack, bluejack, and sand live
oaks are also present. Various grasses and forbs provide ground cover in
the forested and pasture areas.
In 1981, about 15% of the area was cropland, primarily corn and cotton,
and about 5% was pasture. About one-sixth of the area is owned and used
by the federal government for military posts such as Fort Bragg Military
Reservation in North Carolina. Only a small percentage of the land is used
for urban development and other purposes, although several very high quality,
world famous golf courses have been developed. Some orchards and small
commercial fruit and vegetable farms are scattered throughout the area.
This region has an udic moisture regime with average annual precipitation
ranging from 1150 to 1275 mm. Maximum precipitation occurs in the summer
and the minimum is in winter. A thermic temperature regime exists and the
average annual air temperature is 17 to 18°C. The average frost-free
period ranges from 220 to 240 days.
Elevation in MLRA 137 ranges from 50 to 200 m above sea level. The
area is dissected with rolling to hilly uplands. Local relief is only a
few meters, but some hills are 25 to 50 m above adjacent areas.
Precipitation, perennial streams, and ground water are plentiful, however,
low water holding capacity and rapid permeability of the soils severely
limit plant growth unless irrigation water is used. The rolling topography
gives rise to many seeps and springs.
The major soil components making up 1% or more of the total area occupied
by MLRA 137 are shown in Table 2. The
components are listed in descending order of acreage. The area is dominated
by Ultisols, but Psamments occupy about 13% of the area, while Inceptisols
occupy about 8%. Psamments are sandy Entisols and have no zone of clay
Psamments are sand to a depth of at least 100 cm and quartz is the most
dominant mineral. Deep, sandy Quartzipsamments (Lakeland series) and Paleudults
(Blanton and Troup series) occur on rolling and hilly slopes where the
upper sandy layer is thick. Paleudults (Blanton, Dothan, and Fuquay series)
occur where the upper sand strata are thinner and underlain by more clayey
materials. Very poorly drained soils occurring along drainage ways are
Psammaquents (Osier series; 2,805 ha) and Humaquepts (Rutledge series;
4,816 ha). The STATSGO soil map for MLRA 137 is shown in Fig. 1.
Water and Chemical Transport
Except for the Lakeland series, little data on soil water and/or chemical
transport obtained within MLRA 137 has been published. This is probably
due to the limited acreage and the relatively minor agricultural role the
soils within this MLRA have had in the past. Information in other chapters
of this publication deal with several of the soils found in MLRA 137. These
include Norfolk, Wagram,
and Troup in MLRA
133A. The following information on the Blanton and Gilead series stems
from unpublished data collected at North Carolina State University in the
late 1970s in Southern Regional Research project S-125.
The Blanton soil series (loamy, siliceous, thermic, Grossarenic Paleudults)
developed from unconsolidated marine sediments and occurs on nearly level
sites. The sand content has a narrow range, 87 to 94%, throughout the 152-cm
profile. The high bulk density values of 1.63 and 1.64 g cm-3
occurring in the E1 and E2 horizons are indicative of an induced tillage
In situ field capacity of this sandy soil is nearly uniform with depth
(Table 3), but attains its maximum value
of 0.133 cm3 cm-3 in the E2 horizon where the percentage
of sand is least and bulk density is greatest. The available water holding
capacity (AWHC) is essentially constant with depth throughout the profile,
being 0.07 to 0.08 cm3 cm-3.
The saturated water content of the Ap and Bt1 horizons of the Blanton
series is 0.38 to 0.40 cm3 cm-3. Water drains or
is released by the soil at very low soil water pressures. At the -10 kPa
soil water pressure, the water content is only 0.08 to 0.09 cm3
cm-3(Fig. 2A). The water retention relationships for the remaining
horizons of the sandy Blanton material are similar. This low water retention,
which is typical of coarse sandy soils, causes the soil to be droughty.
Saturated hydraulic conductivity values for all seven horizons (Table
3), measured using undisturbed soil cores (Klute and Dirksen, 1986),
exceed 12 cm h-1. In situ unsaturated hydraulic conductivity
K(q) for the various horizons of the Blanton
soil was measured using the instantaneous profile method (Green et al.,
1986). The K(q) in the Ap horizon (0 to 15 cm),
for example, decreases more than three orders of magnitude (from 1 to 0.0002
cm h-1) as volumetric water content decreases from 0.30 to 0.10
cm3 cm-3(Fig. 3). A similar relationship exists for
the remaining six horizons.
The Gilead series (clayey, kaolinitic, thermic, Typic Fragiudults)
is developed on nearly level to sloping land from unconsolidated marine
sediments. Unpublished data for this series from Moore and Harnett counties
in North Carolina are shown in Table 4.
This soil is typified by a sandy surface layer less than 50 cm thick overlying
finer textured material. The change in soil texture between the Ap or E
horizons and the Bt1 is abrupt. For these two pedons, the clay content
increases about 30% at the Bt boundary. An E horizon is present at the
Harnett County site whereas it is absent at the Moore County site where
the Bt horizon is closer to the soil surface. A tillage pan is present
in the E horizon as indicated by the greater bulk density in the E horizon
compared to the Ap horizon.
Water retention at the -33 and -1500 kPa values is much greater in the
clayey Bt horizons compared to the Ap and E horizons (Table
4). Using these data to estimate the available water holding capacity
of the various horizons above the BC horizon, we find the AWHC to be greater
and more variable at the Harnett County site.
Saturated hydraulic conductivity is variable with depth at the Moore
County site (Table 4). The Ksat value
of 9.2 cm h-1 in the Ap horizon decreases to a value of 0.65
cm h-1 in the Bt2 horizon, and then increases in the parent
material. A similar pattern in Ksat vs. depth occurs for the Gilead soil
at the Harnett County site, but the Ksat values in the A, E, and Bt horizons
were less than those for the Gilead profile in Moore County. These large
differences in Ksat between the Ap or E and the Bt horizons often give
rise to perched water tables, which in turn give rise to lateral subsurface
water flow in response to the gravitational gradient.
Water retention curves for Gilead (Fig. 2B) differ from those of Blanton
soil. For Gilead, the sandy Ap horizon has a total porosity of 0.46 cm3
cm-3compared to 0.33 cm3 cm-3in the compact
Bt 3 horizon at the 45 to 61 cm depth. Water retention in the C horizon
is similar to that in the Bt3 . Because the clayey Bt horizons have such
low hydraulic conductivity values, the instantaneous profile method was
ineffective to measure K(q) of the various horizons
deeper than the E horizon. Field-measured K(q)
relations for the Ap and E horizons are shown in Fig. 4. The K(q)
at 0.33 cm3 cm-3water content is about 0.001 cm h-1
. The K(q) values at water contents less than
0.33 cm3 cm-3 were not measured because water
moved into the Bt1 horizon too slowly.
The Lakeland series (thermic, coated, Typic Quartzipsamments) (Table
5) consists of very deep, excessively drained, rapidly permeable soils
that formed in thick deposits of eolian or marine sands. These soils are
found on broad nearly level to very steep uplands, however, slope typically
ranges from 0 to 12%. The sand extends to a depth of at least 2 m. Small
pockets of light gray or white sand grains or yellow or brown mottles occur
in some pedons. It appears that some profiles of Lakeland in MLRA 137 have
thin layers or lenses of finer textured material alternating with the coarser
sand in the lower part of the profile. The presence of these lenses can
increase the water holding capacity of the soil and decreases the saturated
These soils are excessively drained and the depth to the seasonal water
table exceeds 2 m. Natural vegetation consists of drought resistant trees
such as blackjack, turkey oak, and longleaf pine. Some acreage of this
series is used for high risk farming. Without irrigation water the chance
of losing a crop to drought is high due to the low water holding capacity
of the soil. The risk of leaching agricultural chemicals out of the root
zone is high.
The unsaturated hydraulic conductivity as a function of soil water content
for six depth increments of Lakeland in Hoffman, North Carolina is shown
in Fig. 5. Much additional soil physical property data for the Lakeland
series is available in Southern Cooperative Series Bulletin 262 (Dane et
Management and Solute Transport Implications
Efficient water management is a challenge for the deep sandy soils
in MLRA 137. Water from rainfall or irrigation infiltrates the soil rapidly
thereby causing runoff and soil erosion to be minimal. However, the low
AWHC associated with each soil horizon retains only a small amount of infiltrating
water. Thus, the infiltrating water moves down below the rooting zone of
most field, tree, and pasture crops. Therefore, this soil is drougthy and
agricultural crops are grown at considerable risk unless irrigated. If
the soil is irrigated, a high level of water management is required to
minimize percolation losses of water below the root zone.
Due to the low AWHC, high infiltration rate, rapid drainage, and low
cation exchange capacity (CEC), leaching losses of chemicals can occur
. Due to the very low CEC, both cations and anions are subject to leaching
to depths below 1 m. Water and solutes moving vertically downward in these
soils eventually encounter a less permeable layer thus giving rise to lateral
transport. Some of this downward moving water may eventually intercept
an impermeable layer and be transported horizontally until it surfaces
at springs and seeps.
Dane, J.H., D.K. Cassel, J.M. Davidson, W.L. Pollans, and V.L. Quisenberry.
1983. Physical characteristics of soils of the Southern Region-Troup and
Lakeland. p. 258. Cooperative Series Bulletin 262. Auburn, Alabama.
Green, R.E., L.R. Ahuja, and S.K. Chong. 1986. Hydraulic conductivity,
diffusivity, and sorptivity of unsaturated soils: Field methods. In: A.
Klute (ed.). Methods of Soil Analysis, Part 1, Agronomy 9. 2nd
ed. p 771-798. Am. Soc. Agron. Madison, Wisconsin.
Klute, A., and C. Dirksen. 1986. Hydraulic conductivity and diffusivity:
Laboratory methods. In: A. Klute (ed.). Methods of Soil Analysis, Part
1, Agronomy 9. 2nd ed. pp. 687-734. Am. Soc. Agron. Madison,
USDA. 1981. Land resource regions and major land resource areas of the
United States. Agriculture Handbook 296. p. 156. U.S. Government Printing
Office. Washington, D.C.