evaluation of permeability estimates for soils in the
TRANSCRIPT
PERMEABILITY ESTIMATES FOR SOILS IN THE SOUTHERN
PIEDMONT OF GEORGIA
by
MARIA EUGENIA ABREU
(Under the Direction of Larry T. West)
ABSTRACT
A combination of different characteristics may affect the permeability behavior of a soil.
Saturated hydraulic conductivity or permeability (Ks) was measured in situ at five sites in the
Georgia Piedmont in order to examine relationships between Ks and soil morphological features.
At each site, Ks was measured at seven locations on each of the three transects extending from
summit to footslope components of the hillslope. At each location Ks was measured at three
different depths with a compact constant head permeameter. Lab analyses were conducted with
samples taken from the field to associate morphological features with soil permeability behavior.
Results of this study indicate that field Ks measurements varied according to the parent material
that developed that soil. Soils with considerably high permeability typically developed from
felsic parent material and soils with low permeability typically originated from mafic parent
materials. For each location within a site, horizon nomenclature had a great impact on the
movement of water and these differences were further analyzed in the lab. Particle size
distribution, bulk density, and CEC were examined to provide detailed information about horizon
characteristics. Landscape (hillslope) was not a major factor affecting the field Ks and no pattern
was observed for the hillslope component.
INDEX WORDS: Saturated hydraulic conductivity, Ks, particle size distribution, bulk density
PERMEABILITY ESTIMATES FOR SOILS IN THE SOUTHERN
PIEDMONT IN GEORGIA
By
MARIA EUGENIA ABREU
Ing. Agr., Universidad de la Republica, Uruguay, 1999
A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment
of the Requirements for the Degree
MASTER OF SCIENCE
ATHENS, GEORGIA
2005
© 2005 Maria Eugenia Abreu All Rights Reserved
PERMEABILITY ESTIMATES FOR SOILS IN THE SOUTHERN
PIEDMONT IN GEORGIA
By
MARIA EUGENIA ABREU
Major Professor: Larry T West
Committee: Miguel L. Cabrera David E. Radcliffe
Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia December 2005
iv
ACKNOWLEDGEMENTS
The author thanks Dr. Larry West for his guidance during completion of the research and
for serving as chair of the advisory committee. I would like to acknowledge the participation of
Dr. David Radcliffe on the committee and on the discussion of my research. Special thanks and
gratitude for constant support and encouragement is expressed to Dr. Miguel Cabrera. I would
like to thank the entire staff of the USDA-NRCS for their help in this study. Specifically, I
would like to acknowledge Bob Evon, Jim Lathem, Sherry Carlson, and Curtis Marshall for their
assistance with the description of the soils, and for their collaboration in taking Ks measurements
in the field. Acknowledgements also extend to Scott Stanfill, Coby Smith, Troy Smith, Charles
Moore, Gus McCormick, Shelby Finch, and Vicki Hufstetler for their collaboration on taking the
samples in the field, and for their help with the lab work. I would like to recognize the valuable
contribution of Dr. Dory Franklin, George Granade, Dinku Endale, Bob Evon, and Curtis
Marshall in providing me with the sites to work on my research. I’m grateful to Dave Butler for
his support and assistance in processing and analyzing the data of this project.
v
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ...........................................................................................................iv
LIST OF TABLES..........................................................................................................................vi
LIST OF FIGURES.......................................................................................................................vii
INTRODUCTION .........................................................................................................................1
CHAPTER
1 LITERATURE REVIEW ................................................................................................5
2 FIELD SATURATED HYDRAULIC CONDUCTIVITY RELATED TO HORIZON
AND LANDSCAPE POSITION IN THE SOUTHERN PIEDMONT IN
GEORGIA, USA …..............................................................................................16
3 RELATIONSHIPS OF LABORATORY MEASURED SOIL PROPERTIES TO
SATURATED HYDRAULIC CONDUCTIVITY FOR SELECTED SOILS
FROM THE GEORGIA PIEDMONT, USA……………………….....................43
CONCLUSIONS AND IMPLICATIONS....................................................................................64
APPENDICES...............................................................................................................................66
vi
LIST OF TABLES
Page
Table 2.1: General texture and structure by depth for all sites......................................................29
Table 2.2: Analysis of variance of Ks data as affected by site, hillslope, and depth…………….30
Table 2.3: Analysis of variance of Ks data as affected by site, hillslope, and horizon…………..31
Table 3.1: Particle size, bulk density, CEC and Ks for selected pedons.………………………..53
Table 3.2: Analysis of variance of Ks data for all sites as affected by moist and dry bulk density,
COLE, and clay content………………………………………………………………….58
Table 3.3: Analysis of variance of Ks data for sites 1, 2, 3, and 5 as affected by moist and dry
bulk density, COLE, clay content, CEC, and clay activity………………………………58
vii
LIST OF FIGURES
Page
Figure 2.1: Distribution of Ks by depth at site 1…..…………………………………..…............32
Figure 2.2: Distribution of Ks by depth at site 2…………………………………………............33
Figure 2.3: Distribution of Ks by depth at site 3…………………………………………............34
Figure 2.4: Distribution of Ks by depth at site 4.................................….......................................35
Figure 2.5: Distribution of Ks by depth at site 5…………………………………………............36
Figure 2.6: Distribution of Ks by site for shallow depth …...…………………………................37
Figure 2.7: Distribution of Ks by site for middle depth …..……………......................................38
Figure 2.8: Distribution of Ks by site for deep depth……….........................................................39
Figure 2.9: Distribution of Ks by horizon for all sites...................................................................40
Figure 2.10: Distribution of Ks data at site 1 for all depths .….....................................................41
Figure 2.11: Distribution of Ks data at site 2 for all depths .….…………………………………42
Figure 3.1: Mean percentage (%) of clay, silt and sand by depth for all sites……………….…..59
Figure 3.2: Relationship between Ks and clay.………………….……………………………….60
Figure 3.3: Relationship between Ks and COLE ..…………………...………………………….61
Figure 3.4: Relationship between Ks and CEC…………………………………………………..62
Figure 3.5: Relationship between Ks and clay activity ………………………………………….63
1
INTRODUCTION
Saturated hydraulic conductivity (Ks) or “permeability” is one of the more often used
properties for evaluating soil suitability and predicting the fate of anthropogenic materials
applied on or in soil. This property is often estimated in the field or taken from soil survey
databases. Texture, clay mineralogy, bulk density, and cementation influence a horizon’s Ks
(Soil Survey Division Staff, 1993). Pedogenic structure can also affect Ks of structured horizons
because of the network of macropores formed between peds (Bouma et al., 1983; Southard and
Buol, 1988; Bouma, 1991; Tyler et al., 1991; Vervoot et al., 1999).
No single physical property appears to provide specific information of all hydraulic
parameters of a soil horizon, although aggregation or structure is clearly the predominant
component for estimating macropore flow rate and hydraulic parameters dominated by
macropore flow, such as Ks. Although bulk density and total porosity partially indicate soil
structure, these properties do not contain sufficient information regarding soil-pore size
distribution, especially macroporosity (Lin et al., 1999). For this reason, data in addition to
porosity are needed for Ks estimates. Because it is easy to estimate in the field, texture is often
the property given the greatest weight in estimates of Ks, although texture by itself cannot
correctly predict Ks (Lin et al., 1999).
This study will be concerned mainly with the hydraulic properties of soils in the Georgia
Piedmont. The Southern Piedmont land-resource area is dominated by Ultisols. The Bt horizons
of these soils typically have clay textures, and the clay is dominated by such low-activity clays
such as kaolinite and hydroxy-interlayered vermiculite. The most common local soil is the Cecil
soil (Soil Survey Division Staff, 1993). This soil is one of the most extensive soils in the
southeastern United States (West et al., 1998).
2
In these soils, the maximum clay content typically occurs in the upper Bt horizon and
gradually decreases with depth to a minimum in C horizons (Perkins, 1987). Because of the
reliance on clay content for estimates of Ks, upper Bt horizons have minimum estimated Ks in the
profile. In contrast to these estimates, limited data for soils in the Piedmont indicate that clayey
upper Bt horizons often have higher Ks than subjacent BC horizons (Bruce et al., 1983; O'Brien
and Buol, 1984; Vepraskas et al., 1996).
If Ks relationships derived from these limited studies (i.e., the Ks is highest in the upper
Bt horizons) hold true for a wide range of soils and landscapes in the Piedmont, then current
estimates of Ks in soil survey databases do not reflect true relative rates of water movement
through these soils. For example, for a Cecil soil at a depth of 20-28 cm (Bt1 and lower Bt)
corresponds to a Ks of 37-122 cm d-1 (Lathem and Thomas, 2004). Thus, the objectives of this
research are: (1) to determine Ks for major horizons of common soils in the Piedmont of Georgia,
(2) to develop relationships between Ks and morphological properties of these horizons, and (3)
to suggest landscape and/or morphological features that can be used to infer Ks from disturbed
soil (bucket auger) observations.
The first part of this study evaluates the Ks in situ in relation with the site, hillslope, and
depth. The second part evaluates soil morphological features in the lab, with samples taken from
the field from the first study. My null hypotheses are: a) that pedogenic structure, within certain
textures, does not have a major influence on Ks in Piedmont soils and b) that morphological
properties observable in disturbed samples cannot be used to infer Ks.
References
Bouma, J. 1991. Influence of soil macroporosity on environmental quality. Adv. Agron. 46:1-37.
3
Bouma, J., C. Belmans, L.W. Dekker, and W.J.M. Jeurissen. 1983. Assessing the
suitability of soils with macropores for subsurface liquid waste disposal. J. Environ. Qual.
12:305-311.
Bruce, R.R., J.J. Dane, V.L. Quisenberry, N.L. Powell, and A.W. Thomas. 1983. Physical
characteristics of soils in the Southern Region: Cecil. Southern Coop. Series Bull. 267.
Lin H.S., K.J. McInnes, L.P. Wilding, and C.T. Hallmark. 1999a. Effects of soil
morphology on hydraulic properties: I. Quantification of soil morphology. Soil Sci. Soc.
Am. J. 63:948-954.
Lin H.S., K.J. McInnes, L.P. Wilding, and C.T. Hallmark. 1999b. Effects of soil
morphology on hydraulic properties: II. Hydraulic pedotransfer functions. Soil Sci. Soc.
Am. J. 63:955-961.
O'Brien, E.L., and S.W. Buol. 1984. Physical transformations in a vertical soil-saprolite
sequence. Soil Sci. Soc. Am. J. 48:354-357.
Perkins, H.F. 1987. Characterization data for selected Georgia soils. Special Publ. 43.
Georgia Agric. Exp. Stn., Athens, GA.
Soil Survey Division Staff, 1993. Soil survey manual. Agric. Handbook 18, USDA-
NRCS. U.S. Government Printing Office, Washington, D.C.
Lathem, J.R., and G.J. Thomas. 2004. Soil Survey of Jasper County, Georgia, 2004. USDA-
NRCS. U.S. Government Printing Office, Washington, D.C.
Southard, R.J., and S.W. Buol. 1988. Subsoil saturated hydraulic conductivity in relation
to soil properties in the North Carolina Coastal Plain. Soil Sci. Soc. Am. J. 51:1091-1094.
Tyler, E.J., E.M. Drozd, and J.O. Petersen. 1991. Estimating wastewater loading rates
4
using soil morphological descriptions. p. 192-200. In On-site wastewater treatment. Proc.
Sixth National Symposium on Individual and Small Community Sewage Treatment. Am.
Soc. Agric. Eng., St. Joseph, MI.
Vepraskas, M.J., W.R. Guertal, H.J. Kleiss, and A. Amoozegar. 1996. Porosity factors
that control the hydraulic conductivity of soil-saprolite transition zones. Soil Sci. Soc.
Am. J. 60:192-199.
Vervoot, R.W., D.E. Radcliffe, and L.T. West. 1999. Soil structure development and
preferential solute flow. Water Resour. Res. 35:913-928.
West L.T., F.H. Beinroth, M.E. Summer, and B.T. Kang. 1998. Ultisols: Characteristics
and impacts on society. Adv. Agron. 63:179-236.
5
CHAPTER I
LITERATURE REVIEW
Soils in the Piedmont
The Southern Piedmont region of the USA including the Piedmont of Georgia, extends
from Alabama to Virginia. Ultisols are dominant soils in this region. These soils are extensive
in humid-warm temperate or humid-tropical climates. Most have developed under forest
vegetation and contain either an argillic or a kandic horizon. The base saturation is less than
35%. Other minor soils in the Georgia Piedmont are Entisols, Inceptisols, and Alfisols (West et
al., 1998; Bandaratillake, 1985).
Ultisols and Cecil series
Ultisols in the Southern Piedmont have formed mostly from schists, gneisses, and granite
(Strickland, 1971). There are five soil-forming factors: parent material, climate, relief, biota, and
time. Parent material and climate play an especially important role in Ultisol development.
These soils are found on a variety of parent materials, which either contain weatherable minerals
to form silicate clays, or silicate clays were present when the material was deposited. Climate
causes seasonal desiccation and seasonal moisture surplus, which are necessary to form argillic
horizons. Termites and ants may also play a role in the formation of Ultisols, and geomorphic
stability over long periods of time is necessary for Ultisol formation. Statements about the time
factor in Ultisol formation are speculative, because it is difficult to determine when geogenesis
ends and pedogenesis begins (West et al., 1998).
The Cecil series is classified as being in the clayey, kaolinitic, thermic family of Typic
Kandhapludults (Soil Survey Staff, 2003). This soil, as it derives from granitic parent material,
6
differs from others in structural stability, is easily dispersed, and thus, Ks is sensitive to small
changes in pH and electrolyte concentration (Chiang et al., 1987).
Evidence in soils in the Georgia Piedmont, such as abrupt particle size changes and
differing sand mineralogies, suggests that there may be a cap overlying the residual parent
material. However, clay films are commonly reported in most soils in the Southeast suggesting
that clay translocation is an active process.
Hydraulic Properties of Piedmont soils
Soils in the Piedmont are extensively underlain by residuum and saprolite, the weathering
product of metamorphic and igneous rock. A unique characteristic of the saprolite is that it
retains the original parent rock fabric and structure, but has the density and cohesiveness of soil
(Overbaugh, 1996).
The growing interest regarding the hydraulic properties of saprolite in the Georgia
Piedmont is driven by concerns about the environmental impact of waste disposal on and in soils.
Considering the saprolite is the underlying soil rock strata throughout this region, the need for
detailed information about the hydraulic properties of the saprolite has emerged, especially how
water flows through the saprolite. Saturated hydraulic conductivity is one of the several
parameters important in this water movement (Overbaugh, 1996).
The rolling topography of the Piedmont can affect the hydraulic properties.
Schoeneberger and Amoozegar (1990) measured Ks in different horizons and geomorphic
hillslope components in the North Carolina Piedmont. The highest Ks values obtained in the lab
were found in the Bt horizon at all three geomorphic positions, even though the Bt horizon had
the greatest clay contents in the profile. The Ks values were lowest in the B/C transitional
7
horizons at all three geomorphic positions, and increased with depth into the massive continuous
saprolite of the C horizon. An effect due to geomorphic position was suggested by the data, but
was not statistically verified. Overbaugh (1996) observed the same behavior of Ks along the
profile in another region of Piedmont in the state of Georgia, though a hillslope component was
not considered in this study. The high hydraulic conductivity in the Bt horizon was attributed to
preferential flow of water between the pores associated with the soil structure.
Throughout much of Alabama and western Georgia, the Piedmont is characterized by a
relatively gently dipping regional foliation (Kish et al., 1985). According to Schoeneberger et al.
(1995), Ks can be influenced by foliation or bedding planes, although directional Ks is not as
variable as was initially expected. These results correspond only to a single site where the Ks
measurements were generally low. The behavior of Ks due to foliation could differ from other
soils in the Piedmont and foliation can play an important role in water movement, as observed by
Fleck et al. (1989), who reported greater flow rates parallel to the foliation pattern.
Because of the limited potential for development of extensive surface-water reservoirs,
development of ground water resources offers an attractive alternative for expanding water
needs. In the Piedmont, ground water occurs in the saprolite (Champion, 1989; Guthrie et al.,
1989). Ground water movement and the water-yielding characteristics of these rocks are highly
dependent on secondary permeability related to natural fracturing and weathering. Therefore, the
identification of fracture zones is critical for the location of high capacity bedrock wells
(Ellwood et al., 1989).
Radcliffe et al. (1987) analyzed the infiltration rate on Cecil soils, which comprise two
thirds of the southern Piedmont. Infiltration rate averaged 4.1 mm h-1, although these soils
showed a drastic drop in infiltration capacity with time, like other soil series studied. It seems
8
likely that sandy, granitic soils, such as the Cecil series, may be more prone to dispersion-related
problems involving infiltration, crusting, and soil erosion than soils found on more mafic
materials. The authors suggested that some practices may improve water relations of the Cecil
soil considerably, such as proper management of soil pH, avoidance of high sodium
amendments, and potentially the use of gypsum to maintain high electrolyte levels.
Properties affecting Ks
There are many factors that affect saturated hydraulic conductivity (Ks). Most of these
factors interact with each other and influence the specific Ks in a soil. The main factors affecting
Ks are genetic horizon, texture, clay mineralogy, cementation, pedogenic structure,
macroporosity, and macropore type and continuity. Although soil properties affecting Ks can be
quantified, this is a complex and difficult procedure.
Many studies have attempted to determine how these factors affect Ks. McKeague et al.
(1982) measured Ks in the field and in the laboratory for a wide range of U.S.A. and Canadian
soils with varying texture, structure, and porosity. At the same time, Ks was estimated at each
site, and the results were compared. On average, 45% of the field estimates equaled the
laboratory measurements. These results suggest that it is difficult to estimate Ks when including
all factors and their combinations of morphological features in soils. Thus, much personal
judgment is required in applying estimates. For this specific study, the researchers considered
different combinations of soil morphological features to estimate Ks. Depending on
characteristics of the soil some factors improved the predictability of Ks measurements.
Macroporosity and structure influence the Ks of many soils (McKeague et al., 1982; King
and Franzmeier, 1981). Macropores are large, continuous voids in soil and include structural,
9
shrink-swell and tillage fractures, old root channels, and soil fauna burrows. Macroporosity is
important because it can increase infiltration and may result in bypass flow where water moves
rapidly through the profile (Quisenberry and Phillips, 1976). Groundwater movement is affected
by Ks and is predominantly influenced by the structural components of the soil, or the result of
decomposed roots and borings made by large organisms. Several studies estimated Ks by
observing soil morphology. Results from these studies generally suggest that horizons with low
Ks values were generally massive, compressed, and clayey with few or no macropores
(Schoeneberger and Amoozegar, 1995).
According to King et al. (1981), Ks can be predicted from parent material, genetic
horizon, and texture. Considering parent material itself, the researchers reported that water and
wind-deposited materials have higher Ks than ice-deposited materials. This difference can be
explained by the greater compaction of the glacial till under ice, whereas loess was deposited by
wind in a relatively loose, open manner. The relationship to Ks can be explained by the original
bulk density of the parent material, which is closely related to porosity, and how it changed
during soil formation. In regards to Ks of genetic horizons, the parent material has a different Ks
than the horizons formed from it. On one hand, argillic horizons in loess tend to have lower Ks
than their parent material. On the other hand, argillic horizons formed from till have higher Ks
values than the till parent material. The parent material effect on the Ks also depends on the
morphology of that soil. Thus, fragipans have low Ks values and water-worked materials have
high Ks values. King et al. (1981) suggested that values of Ks can be grouped into homogeneous
classes, based in part on the origin of the material, and then used to estimate Ks for similar soils.
Additionally, McKeague et al. (1982) reported that major factors contributing to high Ks
values are abundant biopores, textures coarser than loamy fine sand, and strong fine to medium
10
blocky structure. In general, King et al. (1981) observed that finer-textured horizons tend to
have lower Ks, but many factors other than texture are also important. However, Ks is not
closely related to texture and this lack of a relationship is potentially a major factor influencing
Ks variability.
Structure
Soil structure is generally defined as the mutual arrangement, orientation, and
organization of the particles in the soil. In surface horizons, it may change greatly with time and
season and it affects the water, air, and heat regimes in the field. Soil structure also influences
the mechanical properties of the soil and can affect the performance of some operations, such as
drainage. An aggregate is a group of two or more primary particles which adhere to each other
more strongly than to surrounding particles. Aggregated structure can be characterized either
qualitatively, by describing the typical shapes of the aggregates, or quantitatively, by measuring
their sizes. Additional methods of characterizing soil structure are based on the size distribution
of pores, the mechanical properties of the soil, or the permeability of the soil to air and water, but
none of these methods has been accepted universally. The formation and stability of soil
aggregates is dependent largely upon the quantity and state of clay. The clay not only cements
aggregates internally, but often also coats over natural aggregates (Hillel, 1971).
Structural properties of a soil, such as the bonding forces between primary particles and
the arrangement of particles to micro- and meso-aggregates (up to 2 mm) remain basically
constant over long periods of time. These properties are affected by particle size distribution,
especially clay content, and clay and soil mineralogy. On the other hand, it is well-known that
the state of the structure, such as size distribution of aggregates and/or pores, pore continuity,
11
bulk density, and saturated hydraulic conductivity, may change within short time periods
(Becher, 1988).
Any determination of aggregate-size distribution is also, in one sense, a determination of
aggregate stability. Recognizing the experience involved in relating aggregate-size
measurements to field phenomena, many researchers have decided to use the stability of the
aggregates rather than aggregate-size distribution as an index of soil structure in the field
(Kemper, 1965). The knowledge of the structure stability is useful in predicting the supply of
water to soil and assessing the effects of management practices and treatments on the physical
condition of soil (Reeve, 1965).
Soil structure plays a major role in determining the hydrologic and chemical environment
in Ultisols, which retain and transmit large amounts of water. Saturated hydraulic conductivity is
a good indicator of the soils ability to drain water. Higher Ks values are consistent with the
observed increase in macropore size, where water flow is quite rapid. However, much of the
water in the subsoil is held in micropores, which conduct water slowly (Arya et al., 1992).
Texture and clay mineralogy
In the Southern Piedmont, felsic parent materials weather to soils with clays dominated
by kaolinite (Hamilton, 2002). Stability of kaolinite makes it the dominant mineral in the clay
fraction of most Ultisols. The presence of kaolinite results in low shrink-swell potential and
relatively favorable water-retention properties. However, appreciable amounts of mica,
vermiculite and smectite occur in many of these soils. Sand and silt fractions are composed
mostly of resistant minerals such as quartz (West et al., 1998). In a study in the North Carolina
Piedmont, Calvert et al. (1980) observed that the initial weathering of feldspar at the rock-
12
saprolite contact is very rapid and results in a variety of minerals, each formed within a specific
microenvironment. Somewhat higher in the profile, halloysite, a dominant component developed
on volcanic ash, recrystallizes into kaolinite via a randomly interstratified transition phase.
Soil texture in the Piedmont of Georgia ranges from sand to clay and includes most of the
textural classes. The most common are sandy loam in the A horizon, sandy clay loam, clay, and
clay loam in the B horizon, and coarser textures in lower horizons (BC and C). Silt percentages
are low in these soils and texture mainly varies with sand and clay contents. The majority of the
soils contain over twenty percent clay in subsoil horizons.
References
Arya, L.M., T.S. Dierolf, B. Rusman, A. Sofyan, and I.P.G. Widjaja-Adhi. 1992. Soil structure
effects on hydrologic processes and crop water availability in Ultisols and Oxisols of
Sitiung, Indonesia. CRSP Bull. No.92-03. NC State Univ., Raleigh, NC.Bandaratillake,
Bandaratillake, H.M. 1985. The influence of forest vegetation on soil characteristics in
the Georgia Piedmont. M.S. Thesis, Univ. of Georgia, Athens, GA.
Becher, H.H. 1988. Soil erosion and soil structure. p.15-20. In J. Dresscher et al. (ed.) Impact
of water and external forces on soil structure. Workshop on Soil Physics and Soil
Mechanics, Hannover, Germany. 1986.
Calvert S.C., S.W. Buol, and S.B. Weed. 1980. Mineralogical characteristics and
transformations of a vertical rock-saprolite-soil sequence in the North Carolina Piedmont:
II. Feldspar alteration products – Their transformations through the profile. Soil Sci. Soc.
Am. J. 44:1104-1112.
Champion, T.M. 1989. Definition of hydrogeologic properties of soil and crystalline
13
rock to determine the nature and extent of contamination at a site in the South
Carolina Piedmont. p.46-55. In C.C. Daniel et al. (ed.) Ground water in the Piedmont,
Proc. Conf. on Ground Water in the Piedmont of the Eastern United States, Charlotte,
NC. 16-18 Oct. 1989. Clemson University, Clemson, SC.
Chiang S.C., D.E. Radcliffe, W.P. Miller, and K.D. Newman. 1987. Hydraulic
conductivity of three southeastern soils as affected by sodium, electrolyte
concentration, and pH. Soil Sci. Soc. Am. J. 51:1293-1299.
Ellwood R.B., R.L. Zelley, and D.A. Smith. 1989. High capacity bedrock wells in the
Piedmont. p.328-335. In C.C. Daniel et al. (ed.) Ground water in the Piedmont, Proc.
Conf. on Ground Water in the Piedmont of the Eastern United States, Charlotte, NC. 16-
18 Oct. 1989. Clemson University, Clemson, SC.
Fleck W.R., and R.K. White. 1989. Effects of remnant foliation on the hydrologic
properties of Piedmont saprolite. p.96-111. In C.C. Daniel et al. (ed.) Ground Water in
the Piedmont, Proc. Conf. on Ground Water in the Piedmont of the Eastern United States,
Charlotte, NC. 16-18 Oct. 1989. Clemson University, Clemson, SC.
Guthrie G.M., and S.S. DeJarnette. 1989. Preliminary hydrogeologic evaluation of the
Alabama Piedmont. p. 293-311. In C.C. Daniel et al. (ed.) Ground Water in the Piedmont,
Proc. Conf. on Ground Water in the Piedmont of the Eastern United States, Charlotte,
NC. 16-18 Oct. 1989. Clemson University, Clemson, SC.
Hamilton, D.A. 2002. Mafic and felsic derived soils in the Georgia Piedmont: Parent
material uniformity, reconstruction, and trace metal contents. M.S. Thesis, Univ. of
Georgia, Athens, GA.
Hillel, D. 1971. Soil and water: Physical principles and processes. In T.T. Kozlowski (ed.)
14
Physiological ecology: A series of monographs, texts, and treatises. Academic Press,
New York.
Kemper, W.D. 1965. Aggregate stability. In C.A. Black (ed.) Methods of soil analysis. Part 1.
ASA Monograph 9. ASA, Madison, WI.
Kemper, W.D., and W.S. Chepil. 1965. Size distribution of aggregates. In C.A. Black (ed.)
Methods of soil analysis. Part 1. ASA Monograph 9. ASA Madison, WI.
King, J.J., and D.P. Franzmeier. 1981. Estimation of saturated hydraulic conductivity
from soil morphological and genetic information. Soil Sci. Soc. Am. J. 45:1153-1156.
Kish, S.A., T.B. Hanley, and S. Schamel. 1985. Geology of the southwestern Piedmont of
Georgia. Dep. of Geology, Florida State Univ., Tallahassee, FL.
McKeague, J.A., C. Wang, and G.C. Topp. 1982. Estimating saturated hydraulic
conductivity from soil morphology. Soil. Sci. Soc. Am. J. 46:1239-1244
Overbaugh, M.J. 1996. Assessment of the hydraulic properties of a soil-saprolite
sequence near Watkinsville, Georgia, Masters Thesis, Department of Geology, University
of Georgia.
Quisenberry, V.L., and R.E. Phillips. 1976. Percolation of surface-applied water in the field. Soil
Sci. Soc. Am. J. 40:484-489.
Radcliffe, D.E., W.P. Miller, and S-C. Chiang. 1987. Effect of soil dispersion on surface
run-off in southern Piedmont soils. Dep. of Agronomy, Univ. of Georgia, Athens, GA.
Schoeneberger, P., and A. Amoozegar. 1990. Directional saturated hydraulic conductivity
and macropore morphology of a soil-saprolite sequence. Geoderma 46:31-49.
Schoeneberger, P.J., A. Amoozegar, and S.W. Buol. 1995. Physical property variation of
a soil and saprolite continuum at three geomorphic positions. Soil Sci. Soc. Am. J.
15
9:1389-1397.
Soil Survey Staff. 2003. Keys to Soil Taxonomy. 9th edition. USDA, NRCS. U. S. Government
Printing Office, Washington, D.C.
Strickland, D.J.. 1971. Soils as an indicator of hardwood potential in the Piedmont of
Georgia. M.S. Thesis, Univ. of Georgia, Athens, GA.
West L.T., F.H. Beinroth, M.E. Summer, and B.T. Kang. 1998. Ultisols: Characteristics
and impacts on society. Adv. Agron. 63:179-236.
16
CHAPTER II
FIELD SATURATED HYDRAULIC CONDUCTIVITY RELATED
TO HORIZON AND LANDSCAPE POSITION IN THE SOUTHERN
PIEDMONT IN GEORGIA, USA
______________________________________________________________________________ 1M.E. Abreu, L.T. West, D.E. Radcliffe, and M. L. Cabrera. To be submitted to Soil Science
Society of America Journal.
17
Abstract
Saturated hydraulic conductivity (Ks) or “permeability” is a key property for soil
interpretations and can have important implications for septic systems, as well as for modeling
movement of compounds in the soil, such as pesticides and nutrients. Measuring Ks is complex,
expensive, and time-consuming. Thus, Ks is typically estimated from soil morphological
features such as texture, clay mineralogy, structure, and porosity. Traditionally, estimates of Ks
for soil horizons have been based primarily on clay content. This parameter is easy to quantify,
but used alone is not accurate for estimation of Ks. Other properties, such as structure, are
difficult to quantify but can predict Ks more accurately. Thus, the objective of this study is to
refine morphology-based estimates of Ks in the southern Piedmont in Georgia, and to examine
the interrelationships between morphological features and their impact on Ks. Ks was measured
in situ at five sites and the soil was described. When considering all the soil components in a
typical Piedmont soil, it is generally suggested that the clayey shallow horizons are more
permeable than deeper horizons. Results of Ks measured in the field supported this behavior for
all sites studied. Primarily, this is due to the network of coarse pores formed by better-expressed
structure in the upper horizons. Differences with depth in Ks are likely related to a combination
of morphological properties, with pedogenic structure having a great impact on Ks. For the five
sites in the Piedmont it was observed that the clayey, well-developed Bt horizons were the most
permeable horizons, with a mean Ks for all sites of 482 cm d-1. The lowest mean Ks of 8.5 cm d-1
was observed at the middle depth, while the deep depth had a mean Ks of 111 cm d-1 (Fig. 2.9).
Mean Ks sites 1 and 3 differed from all other sites, when averaged across sites. Averaged across
all depths, mean Ks was greatest at sites 1 and 3 and least at sites 2, 4, and 5, which did not differ
from each other. Sites 1 and 3 were likely dominated by felsic parent material.
18
Introduction
Saturated hydraulic conductivity is one of the more often used properties for evaluating
soil use suitability. It can contribute to understanding components of nutrient modeling such as
soil fertility and pesticide leaching, assist with pond installation, and give answers for on-site
waste water disposal or septic systems.
Southern Piedmont soils developed over saprolite, derived from weathering of two types
of parent material: mafic and felsic. Mostly felsic parent material underlies the Southern
Piedmont. Soils developed over saprolite with mafic influence (10% of soils in the Southern
Piedmont) have appreciably lower Ks than soils formed from typical felsic saprolite (85% of
soils in the southern Piedmont) (Hamilton, 2002).
Permeability is often estimated in the field or taken from soil survey databases. Texture,
clay mineralogy, bulk density, and cementation influence a horizon’s Ks (Soil Survey Division
Staff, 1993). Pedogenic structure can also affect Ks of structured horizons because of the
network of macropores formed between peds (Bouma et al., 1983; Southard and Buol, 1988;
Bouma, 1991; Tyler et al., 1991; Vervoot et al., 1999).
No single physical property appears to provide specific information of all hydraulic
parameters, although aggregation or structure is clearly the predominant component for
estimating macropore flow rate and hydraulic parameters dominated by macropore flow, such as
Ks. Although bulk density partially indicates soil structure, this property does not contain
sufficient information regarding soil porosity, especially macroporosity (Lin et al., 1999). For
this reason, other data in addition to porosity are needed to predict Ks. These properties are more
difficult to quantify in the field than texture, which is relatively easy to quantify. Thus, texture is
often the property given the greatest weight in estimates of Ks, although texture by itself cannot
19
correctly predict Ks (Lin et al., 1999).
This study focuses mainly on the hydraulic properties of soils in the Georgia Piedmont.
The Southern Piedmont land-resource area is dominated by Ultisols. The Bt horizons of these
soils typically have clay textures, usually dominated by such low-activity clays as kaolinite. The
most common local soil is the Cecil soil (Soil Survey Division Staff, 1993). This soil is one of
the most extensive soils in the southeastern USA (West et al., 1998).
In these soils, the maximum clay content typically occurs in the upper Bt horizon and
gradually decreases with depth to a minimum in C horizons (Perkins, 1987). Because of the
reliance on clay content for estimates of Ks, upper Bt horizons have minimum estimated Ks in the
profile. In contrast to these estimates, limited data for soils in the Piedmont indicate that clayey
upper Bt horizons often have higher Ks than subjacent BC horizons (Bruce et al., 1983; O'Brien
and Buol, 1984; Vepraskas et al., 1996).
If Ks relationships derived from these limited studies (i.e., the Ks is highest in the upper
Bt horizons) hold true for a wide range of soils and landscapes in the Piedmont, then current
estimates of Ks in soil survey databases do not reflect true relative rates of water movement
through these soils. The objectives of this research are: (1) to determine Ks for major horizons of
common soils in the Piedmont of Georgia, (2) to develop relationships between Ks and
morphological properties of these horizons, and (3) to suggest landscape and/or morphological
features that can be used to infer Ks from disturbed soil (bucket auger) observations.
Materials and Methods
Site selection
Five sites in the Southern Piedmont in Georgia were selected for this research. All sites
20
were long-term pasture and represented a range of slopes between 5 to 20%, and local relief
typical for Piedmont landscapes. Mostly Cecil and related series such as Pacolet and Appling
(fine, kaolinitic, thermic Typic Kanhapludults) were considered, because they comprise more
than 50% of the soils mapped in the Southern Piedmont. Soils considered in this research were
mainly developed over saprolite with felsic influence, which gives them a relatively high
permeability.
In May 2004, the selection of the first site in Oconee County near Watkinsville (site 1; N
33º 61.897’ W 83º 29.252’) was established. The other four sites were located in Taliaferro
county near Crawfordville (site 2; N 33º 31.734’ W 82º 54.830’), Oconee county near Bishop
(site 3; N 33º 47.152’ W 83º 23.009’), Fulton County near Palmetto (site 4; N 33º 31.581’ W 84º
41.366’), and Spaulding county near Griffin (site 5; N 33º 15.476’ W 84º 18.015’). In general,
the same experimental methods were used at each site, though there were some modifications
while the research developed.
Ks measurement
On each site, 21 equally-spaced locations along three transects that extended from
summit to footslope positions were selected. The length of the transect from the highest point on
summit to footslope was at least 100 m with no maximum. Alluvium at the base of the slope was
avoided. At each location, the soil was described and Ks was measured at three different depths.
Holes were dug to a 140 cm depth with a bucket auger, the landscape position was described, the
slope was measured with a clinometer, and the location determined with global positioning
system (GPS) of a 5 m resolution. The soil was described from bucket auger borings using
standard terminology (Soil Survey Division Staff, 1993). Based on this description, the shallow
21
measurement depth was set to be in the upper 25 cm of the Bt horizon. The same holes used for
descriptions served as locations where Ks was measured at the fixed deepest depth (1.40 m). In
order to measure Ks at middle and shallow depths, another hole was dug at a 1-m distance from
the original hole. Middle and shallow depths were different for each location and were
determined according to depth of horizons from the previous soil bucket auger description.
A custom-made borehole permeameter similar to a Compact Constant Head Permeameter
(CCHP) was used to measure Ks in situ (Amoozegar, 1989). A cylindrical 10-cm diameter auger
hole was bored to the desired depth. Plastic tanks served as a water supply reservoir when taking
the measurements, and were connected by a hose to a device placed inside the hole, with the
purpose to maintain a constant head of water once the soil was saturated. The bottle provided a
means for supplying the water to the infiltration surface and a means to measure the flow rate
into the soil, given by the loss of water in the tank. A borehole equation developed by Elrick and
Reynolds (1992) was used to convert percolation rate to Ks, where the macroscopic capillary
length and G (a geometric factor estimated with equations from Bosch and West (1997) were
estimated from texture and structure to solve for Ks.
Before taking the measurements, the soil was saturated for 30 min with a 0.02-M CaCl2
solution to avoid clay dispersion from the walls of the hole. After saturation, measurements
were taken every 30 min with a head of 5 cm. Measurements were taken in cm, considering the
amount of water passing through a certain soil horizon over time. The loss of water from the
tank was recorded and equivalence was established in the lab to convert depth of water in the
tank into volume. For the purpose of coefficient calculation, every soil was considered to be
structured from clay. In this way, Ks was established for a certain head and horizon, in a
determined landscape position in a specific site.
22
Statistical Analysis
PROC GLM (SAS Institute Inc., Cary, NC) was used to analyze the measurements taken
in the field to determine the differences and relationships among depth, hillslope position, and
site. Means of Ks values were separated using Fisher’s LSD (P<0.05). These data were also
analyzed to determine the existence of spatial correlation among measurements on each site for
the hillslope component, within depths.
Spatial analyses were developed to determine the correlation between the measurements
and the hillslope component. A variogram was fitted for each depth by site, and was analyzed by
PROC VARIOGRAM (SAS Institute Inc., Cary, NC). Scatterplots were also examined to
observe the distribution of the data with latitude and longitud (PROC GCONTOUR).
Results and discussion
Ks in situ
Mean Ks measured with the borehole permeameter over all hillslopes and locations were
482, 8.5, and 111 cm d-1 for upper Bt, middle Bt , and BC horizons, respectively. Classes of Ks
values were referenced to USDA-NRCS (Soil Survey Staff, 1993) classification, where a very
high Ks corresponds to more than 100 µm s-1 (648 cm d-1), and a very low Ks corresponds to less
than 0.01 µm s-1 (0.0648 cm d-1). Mean Ks values for all locations at site 1 were 1593, 12 and
310 cm d-1 for shallow, middle and deep depths, respectively (Fig. 2.1). At site 2, Ks values for
the same depths were 9.2, 4.4 and 3.4 cm d-1 (Fig. 2.2). Values of Ks were 640, 2.3 and 145 cm
d-1 for site 3, (Fig. 2.3) and 89, 14 and 62 cm d-1 for site 4 (Fig. 2.4), and 56, 9.5 and 26 cm d-1
for site 5 (Fig. 2.5) for shallow, middle, and deep depths respectively. Given the data, Ks values
observed at four of the sites were moderately high and high, whereas one of the sites (Site 2) was
moderately low. This is possibly related to the parent material from which the soil originated.
23
Such significant differences suggest that sites 1 and 3 were developed from felsic parent
material, whereas mafic parent material has influenced properties of the soil on site 2. Data
suggest that the soils on sites 4 and 5 were originated from felsic parent material with some
possible influence from mafic parent material.
Distribution with depth
Variation in soil morphology was observed with depth. The shallow depth included the
upper Bt horizons. Middle depths included either the lower Bt or BC horizons, and deep depths
the BC, CB or C horizons. At every location at every site, upper Bt horizons (shallow depth) had
the highest clay contents. At most sites, texture at shallow depths ranged between clay and
sandy clay, with clay being the most common texture for the Bt horizons (Table 2.1). Lower Bt
horizons (middle depth) had a sandy clay, sandy clay loam, or clay loam texture. Clay was
substantially lower in BC horizons (either middle or deep depth), usually having a sandy clay
loam or clay loam texture. The same consistent behavior was also observed for soil structure.
Typically, Bt horizons presented a well-developed structure, usually consisting of moderate
medium subangular blocky (Table 2.1). Less developed structure was observed in underlying
horizons, usually weak medium or fine subangular blocky structure or massive at a few sites.
Platy structure was also observed at the middle depth. The deepest measurement depth usually
consisted of sandy clay, sandy clay loam or sandy loam textures. Structure at the deep depth
consisted of either weak subangular blocky structure or massive, corresponding to CB or C
horizons.
Results showed that for all sites the shallow depth had the highest Ks (note that all graphs
are at different scales). For three of the sites (sites 1, 4, and 5), Ks at the middle depth was the
24
lowest (Figs. 2.1, 2.4, and 2.5). Site 1 presented the greatest difference between the shallow and
middle depth (Fig. 2.1). At site 1 mean Ks at the shallow depth was greater than the middle and
deep depths (P < 0.05), which did not differ (Fig. 2.1). At sites 4 and 5, mean Ks at the shallow
depth was greater than the middle depth (P < 0.05). The deep depth did not differ from shallow
and middle depths at sites 4 and 5 (Figs. 2.4 and 2.5). These differences among depths could be
explained by the morphological variation in the soil profile. Shallow depths (Bt horizon) had
more clay content than deeper horizons and better developed structure. The lower Ks of the
middle depth (Bt or BC) compared to the shallow depth, can be explained by a less developed
structure with a relatively high clay content. At the deep depth there was either no structure or
weak structure, but the clay content was low, which allowed the Ks to increase in relation with
the middle depth.
For site 1, high Ks was observed at all depths (Fig. 2.1). Conversely, site 2 showed low
Ks for all depths, while at site 3 intermediate values were observed for all depths (Fig. 2.2 and
2.3). Sites 4 and 5 consisted of low values, especially for the middle depth (Fig. 2.4 and 2.5).
Site 2 may have developed from mafic rocks, which give soils a low Ks, as observed for this site.
The other four sites may have developed from felsic parent materials, and showed higher Ks
values. It is possible that sites 4 and 5 have a mafic influence on their formation, explaining the
intermediate Ks observed at these sites.
Statistical analysis showed that the Bt and CB horizons were similar and higher than the
Bt2 and BC, which were also similar to each other. Mean Ks values for the Bt and CB horizons
were 479 and 496 cm d-1, respectively. The BC horizon had a mean Ks value of 15 cm d-1, and
for the Bt2 was 13 cm d-1 (Fig. 2.9).
25
Spatial analysis of landscape position
Permeability of soils was spatially analyzed for each site considering measurements on
different hillslope components. The three different measurement depths were considered
separately, therefore, three sets of data are presented according to depth (Figs. 2.1 to 2.5).
The scatterplots for the shallow, middle, and deep depths showed that higher and lower
permeabilities were not arranged in a specific pattern, i.e. there was no visible trend in the data.
When related to landscape position, Site 2 had a weak trend to upper landscape positions to have
higher Ks than lower positions (Fig. 2.11). However, this trend was not observed at the other
sites, for example Site 1 (Fig. 2.10). Variograms confirmed the lack of spatial relationship
between Ks and position along the hillslope (not shown). No noticeable pattern was observed
and the differences were not significant.
As a result of the variogram procedure, the fitted variogram was linear for all depths.
Overall, analysis indicated that there was no spatial correlation between Ks and landscape
position for any of the three depths, even though different patterns of Ks were observed at
different sites in relation to landscape position. No particular pattern was observed along the
hillslope transects, possibly because Ks is influenced by many morphological features and their
interactions. The morphology in these landscapes is generally not related to the hillslope
component.
Correlation among factors
Differences in Ks measurements were observed among sites and depths, while hillslope
didn’t affect the measurements taken in situ (Table 2.2). Additionally, the differences among
sites were not the same for all depths, given a significant interaction. When considering horizon
26
as a parameter instead of depth, the same model was fitted in relation to site and hillslope, and
their interactions (Table 2.3). Differences in Ks among depths were significant and appear to be
related to a combination of horizon texture and pedogenic structure. The difference in
permeability for different depths had a trend with the horizons at shallow depths having higher
Ks values than underlying horizons at sites 1, 4, and 5 (Figs. 2.1, 2.4, and 2.5). Measurements of
Ks at middle and deep depths were lower than upper Bt horizons (shallow depth), and were not
significantly different from each other at all sites. At sites 2, 3, 4, and 5 one of either middle or
deep depth was different from the shallow depth (Figs. 2.2 to 2.5). When considering the depths
as independent measurements, the shallow depth was higher in permeability and significantly
different from horizons underneath.
Conclusions
Given the five sites within the Georgia Piedmont, most of them had a moderately high
Ks, even differences were observed within each site. Most of the sites were developed from a
felsic parent material, and certainly, soils developed over saprolite with felsic influence have
higher Ks than those developed from mafic parent material. For all locations within a site, there
was a difference in the soil profile among depths. For upper Bt horizons (shallow depth), the
texture was clayier than deeper horizons and had considerably higher Ks values, which was likely
due to a well-developed structure. The more clayey horizons had more strongly expressed
structure and higher Ks than underlying horizons. One possible explanation for this can be
derived from the fact that the more clay content, the more the soil development, which implies a
more developed structure and consequently higher Ks values. The modification of soil structure
may affect the hydraulic properties by affecting the pore-size distribution on the soil.
Apparently, the landscape position doesn’t have a great impact on the Ks in situ at any
27
depth of measurement and there is no significant spatial correlation of hillslope component for
shallow, middle, and deep depths. The main differences observed in the hydraulic properties
appear to be associated with depths and horizons for the soils evaluated.
References
Ammozegar, A. 1989. A compact constant-head permeameter for measuring saturated hydraulic
conductivity of the vadose zone. Soil Sci. Soc. Am. J. 53:1356-1361.
Bouma, J. 1991. Influence of soil macroporosity on environmental quality. Adv. Agron. 46:1-37.
Bouma, J., C. Belmans, L.W. Dekker, and W.J.M. Jeurissen. 1983. Assessing the
suitability of soils with macropores for subsurface liquid waste disposal. J. Environ. Qual.
12:305-311.
Bruce, R.R., J.J. Dane, V.L. Quisenberry, N.L. Powell, and A.W. Thomas. 1983. Physical
characteristics of soils in the Southern Region: Cecil. Southern Coop. Series Bull. 267.
Buckingham, E. 1907. Studies on the movement of soil moisture. Bulletin 38. U.S. Department
of Agriculture Bureau of Soils, Washington, DC.
Hamilton, D.A. 2002. Mafic and felsic derived soils in the Georgia Piedmont: Parent
material uniformity, reconstruction, and trace metal contents. M.S. Thesis, Univ. of
Georgia, Athens, GA.
Lin H.S., K.J. McInnes, L.P. Wilding, and C.T. Hallmark. 1999a. Effects of soil
morphology on hydraulic properties: I. Quantification of soil morphology. Soil Sci. Soc.
Am. J. 63:948-954.
Lin H.S., K.J. McInnes, L.P. Wilding, and C.T. Hallmark. 1999b. Effects of soil
28
morphology on hydraulic properties: II. Hydraulic pedotransfer functions. Soil Sci. Soc.
Am. J. 63:955-961.
O'Brien, E.L., and S.W. Buol. 1984. Physical transformations in a vertical soil-saprolite
sequence. Soil Sci. Soc. Am. J. 48:354-357.
Perkins, H.F. 1987. Characterization data for selected Georgia soils. Special Publ. 43.
Georgia Agric. Exp. Stn., Athens, GA.
SAS Institute. 2000. The SAS® system for WindowsTM, Release 8.1. SAS Inst., Cary, NC.
Soil Survey Division Staff, 1993. Soil survey manual. Agric. Handbook 18, USDA-
NRCS. U.S. Government Printing Office, Washington, D.C.
Southard, R.J., and S.W. Buol. 1988. Subsoil saturated hydraulic conductivity in relation
to soil properties in the North Carolina Coastal Plain. Soil Sci. Soc. Am. J. 51:1091-1094.
Tyler, E.J., E.M. Drozd, and J.O. Petersen. 1991. Estimating wastewater loading rates
using soil morphological descriptions. p. 192-200. In On-site wastewater treatment. Proc.
Sixth National Symposium on Individual and Small Community Sewage Treatment. Am.
Soc. Agric. Eng., St. Joseph, MI.
Vepraskas, M.J., W.R. Guertal, H.J. Kleiss, and A. Amoozegar. 1996. Porosity factors
that control the hydraulic conductivity of soil-saprolite transition zones. Soil Sci. Soc.
Am. J. 60:192-199.
Vervoot, R.W., D.E. Radcliffe, and L.T. West. 1999. Soil structure development and
preferential solute flow. Water Resour. Res. 35:913-928.
West L.T., F.H. Beinroth, M.E. Summer, and B.T. Kang. 1998. Ultisols: Characteristics
and impacts on society. Adv. Agron. 63:179-236.
29
Table 2.1. General texture and structure by depth for all sites
Depth Texture Structure Horizon
Shallow Clay
Sandy clay
Moderate medium
subangular blocky
Bt
Bt1
Middle Sandy clay
Clay loam
Sandy clay loam
Weak medium and
fine subangular
blocky
Bt2
BC
Deep Sandy clay
Sandy clay loam
Sandy loam
Weak subangular
blocky
Massive
CB
C
30
Table 2.2. Analysis of variance of Ks data as affected by site, hillslope, and depth
Source DF P-value‡
Model 104 ***
Site 4 ***
Hillslope 6 NS
Depth 2 ***
Site*Hillslope 24 NS
Site*Depth 8 ***
Hillslope*Depth 12 NS
Site*Hilslope*Depth 48 NS
Error 201
‡ P-values < 0.1=†, < 0.05=*, < 0.01=**, < 0.001=***
31
Table 2.3. Analysis of variance of Ks data as affected by site, hillslope, and horizon.
Source DF P-value‡
Model 104 ***
Site 4 ***
Hillslope 6 NS
Horizon 2 ***
Site*Hillslope 24 NS
Site*Horizon 8 ***
Hillslope*Horizon 12 NS
Site*Hilslope*Horizon 48 NS
Error 201
‡ P-values < 0.1=†, < 0.05=*, < 0.01=**, < 0.001=***
32
Figure 2.1. Distribution of Ks by depth at site 1
Shallow Middle Deep
Ks
(cm
d- 1
)
0
200
400
600
800
1000
1200
1400
1600
1800a
b
b
33
Figure 2.2. Distribution of Ks by depth at site 2
Shallow Middle Deep
Ks
(cm
d- 1
)
0
2
4
6
8
10a
abb
34
Figure 2.3. Distribution of Ks by depth at site 3
Shallow Middle Deep
Ks
(cm
d-1
)
0
100
200
300
400
500
600
700a
ab
b
35
Figure 2.4. Distribution of Ks by depth at site 4
Shallow Middle Deep
Ks
(cm
d- 1
)
0
20
40
60
80
100a
ab
b
36
Figure 2.5. Distribution of Ks by depth at site 5
Shallow Middle Deep
Ks
(cm
d- 1
)
0
10
20
30
40
50
60 a
ab
b
37
Figure 2.6. Distribution of Ks by site for shallow depth
Site 1 Site 2 Site 3 Site 4 Site 5
Ks
(cm
d-1
)
0
200
400
600
800
1000
1200
1400
1600
1800a
b
c cc
38
Figure 2.7. Distribution of Ks by site for middle depth
Site 1 Site 2 Site 3 Site 4 Site 5
Ks
(cm
d-1
)
0
2
4
6
8
10
12
14
16
aa
c
bc
ab
39
Figure 2.8. Distribution of Ks by site for deep depth
Site 1 Site 2 Site 3 Site 4 Site 5
Ks
(cm
d-1
)
0
50
100
150
200
250
300
350a
ab
ab
bb
40
Figure 2.9. Distribution of Ks by horizon for all sites.
Bt1 Lower Bt BC CB C*
Ks
(cm
d-1
)
0
100
200
300
400
500
600
a a
b b
*C horizon not included in statistics because there was not enough data.
41
Figure 2.10. Distribution of Ks data at site 1 for all depths.
summit upper backs. mid backs. lower backs. footslope
Ks
(cm
d-1
)
0
500
1000
1500
2000
2500ShallowMiddleDeep
42
Figure 2.11. Distribution of Ks data at site 2 for all depths.
summit upper backs. mid backs. lower backs. footslope
Ks
(cm
d-1
)
02468
101214161820
ShallowMiddleDeep
43
CHAPTER III
RELATIONSHIPS OF SOIL PROPERTIES TO SATURATED
HYDRAULIC CONDUCTIVITY FOR SELECTED SOILS FROM
THE GEORGIA PIEDMONT, USA
______________________________________________________________________________ 1M.E. Abreu, L.T. West, D.E. Radcliffe, and M. L. Cabrera. To be submitted to Soil Science
Society of America Journal.
44
Abstract
Saturated hydraulic conductivity (Ks) or “permeability” of a soil is the result of the
interaction of various soil properties including texture, structure, mineralogy, and ‘cemented’
horizons. The objective of this study was to relate laboratory-measured properties to Ks
measurements taken in the field. Properties analyzed in the lab included texture, shrink-swell
potential, bulk density, pH, cation exchange capacity (CEC), and water retention characteristics.
In general, Bt and BC horizons consisted of no less than 30% clay, while C, and Ap
horizons contained less than 25% clay. Bt horizons had mean moist and dry bulk density values
of 1.39 g cm-3 and 1.45 g cm-3, respectively. C horizons had the lowest range between moist and
dry bulk density, and thus, a low coefficient of linear extensibility (COLE). The water release
curve (WRC) showed that clayey horizons retained more water than sandier horizons under the
same pressure. Clay was the parameter that best explained Ks (P<0.01), when considering all
sites, with the Bt horizons having the greatest clay content. The estimated parameters were site,
moist and dry bulk density, COLE, and clay. When the COLE was considered in the model for
only sites 1, 2, and 3, it was significantly related to Ks values (P<0.05). Clay content was also
significant for this model (P<0.01). For Site 4, moist and dry bulk density, COLE, clay content,
and pH were analyzed, only clay content was significant in the model (P<0.05). Examination of
soil properties in the lab was useful in better understanding the relationship between those
properties and Ks in the field, and to evaluate which properties may be useful for predicting Ks.
Introduction
The analysis of some properties in the laboratory, such as texture, bulk density, cation
exchange capacity (CEC), and pH can provide important information about soils. The
45
information is more powerful if complemented with field data. In general, measurements of Ks
in the field, particularly for structured soils, will maintain its functional connection with the
surrounding soil (Bouma, 1983). For laboratory analysis this connection is lost, the samples are
disturbed, but the analysis provide complementary information to the field data, to better
understand the whole system.
One of the analyzed features, bulk density, is a soil property indicative of porosity
potential and corresponds to the soil measurement that considers the solid mass of the soil in
relation to the total volume. Thus, bulk soil consists of three dispersed phases: solid, gas, and
liquid, which varies with porosity. Bulk density also varies with texture and structure, and these
properties commonly vary with depth, so it can be thought that bulk density will vary too, among
different horizons. Thomas et al. (2000) studied different physiographic provinces and soils in
relation with shrink-swell potential. In the Piedmont, for granite gneiss and hornblende gneiss
parent materials, having a kaolinitic Typic Kanhapludult and a smectitic Typic Hapludalf,
respectively, the researchers observed a moderate shrink-swell potential for the kaolinitic soil
and very high shrink-swell potential for the smectite soil. More expandable clays (high shrink-
swell) have a lower bulk density and a higher COLE. Bulk density is also correlated with soil
water content. The more solid mass and less pore space present in the soil, the higher the bulk
density.
Particle size distribution (PSD) is the measurement of the size distribution of individual
particles in a soil sample. Comparisons and inferences about other properties can be made by
taking into account the texture in each horizon and considering the profile as a whole. This is
very important because texture affects other characteristics which can be inferred from it, such as
water movement through the soil profile. Thus, permeability and hydraulic properties in general
46
can be predicted using PSD. The CEC to clay ratio can be used as an index of clay mineralogy.
The CEC determination, together with the clay content of a horizon, provide information about
the clay activity.
This study is complementary to a field study which was conducted at five selected sites in
the Georgia Piedmont, where Ks was measured in situ. Samples were taken from the field and
further analyzed in the lab, in order to more precisely characterize soil properties that affect Ks.
The specific studies conducted were particle size analysis, bulk density, pH, CEC, and water
release characteristics. The COLE was determined from the bulk density and the clay activity
from the results of CEC and particle size analysis. The objective was to complement the field
measurement of Ks and to be able to relate soil characteristics to Ks measurements, in order to
provide accurate Ks estimates from field bucket auger borings.
Materials and Methods
Sample collection
Five sites in the Southern Piedmont in Georgia were selected for this research. All sites
represented a range of slopes between 5 to 20%, and local relief typical for a Piedmont
landscape. Mostly Cecil and related series such as Pacolet and Appling (fine, kaolinitic, thermic
Typic Kanhapludults) were present on these hillslopes, because they comprise more than 50% of
the soils mapped in the Southern Piedmont. Soils considered in this research were mainly
developed over saprolite derived from felsic rocks. They are characterized by a low pH, low
base saturation, and high clay content, with kaolinite being the most common clay mineral
(Overbaugh, 1996).
In May 2004, the selection of the first site in Oconee County near Watkinsville (site 1; N
47
33º 61.897’ W 83º 29.252’) was established. The other four sites were located in Taliaferro
county near Crawfordville (Site 2, N 33º 31.734’ W 82º 54.830’), Oconee county near Bishop
(Site 3, N 33º 47.152’ W 83º 23.009’), Fulton County near Palmetto (Site 4, N 33º 31.581’ W
84º 41.366’), and Spaulding county near Griffin (Site 5, N 33º 15.476’ W 84º 18.015’). Three
pedons at each site were selected for detailed description and sampling to represent the range of
Ks measured at the site. Depth distribution of permeability through the profile was also
considered when selecting the locations for sampling. At each site selected, a pit was excavated,
the soil was described using standard terminology (Soil Survey Division Stuff, 1993), and
samples were collected by genetic horizon. Samples from each horizon included bulk samples
and triplicate undisturbed clods for bulk density analysis.
Particle size analysis
Particle size distribution was determined by the pipette and sieving method (Kilmer and
Alexander, 1949). Results of the previous field study showed differences in Ks values among
horizons. As different horizons had differing levels of clay content, clay was determined for
each horizon at every site and related to Ks to determine the relationship between clay content
and Ks values.
Bulk density
Bulk density was determined by the clod method (Soil Survey Laboratory Staff, 1996).
Clods from each horizon were covered with three coats of a solution of saran in acetone in a
proportion of 7 to 1, and slowly saturated. Moist clods were allowed to drain for approximately
1 h, and weight in air and water was determined. Samples were then air-dried for two weeks and
48
placed at 105ºC for 36 to 48 h to obtain oven dry weights. An estimate of shrink-swell potential
was derived as the coefficient of linear extensibility (COLE) by the following equation: [COLE
= (oven dry bulk density/moist bulk density)1/3 -1]. The correlation between Ks and moist and
dry bulk density, and COLE was determined and a regression model was fitted with other
parameters.
Cation exchange capacity
Cation exchange capacity (CEC) was determined for all horizons from three of the sites
(Soil Survey Laboratory Staff, 1996), and used to determine the clay activity, expressed as the
ratio of CEC:clay (cmol (+) 10 g clay-1). For CEC determinations, the soil was saturated with 1
M pH 7.0 solution of NaOAc, and excess of Na removed by ethanol leaching. Sodium retained
was subsequently replaced by leaching the sample with 1 M pH 7.0 solution of NH4OAc. The
Na concentration in the leachate was determined by atomic absorption spectroscopy.
Statistical Analysis
PROC GLM (SAS Institute Inc., Cary, NC) was used to determine the correlation among
soil properties measured in the lab with Ks. Properties analyzed were moist and dry bulk
densities, COLE, clay content, CEC, and clay activity. Each property was also plotted against Ks
values in order to graphically examine the relationship of each with Ks values.
Results and discussion
Particle size distribution
Bt horizons had the highest clay percentage when considering all sites. Clay percentages
49
in the upper Bt horizon ranged from 33.7% at Site 2 to 67.3% at Site 4. The Ap horizons had
mean clay percentages varying between 6.4% (at Site 1) and 28.9% (at Site 4). The C horizons
had clay percentages similar to Ap horizons, ranging from 7.6% at Site 4, to 24.5% at Site 2.
The BC horizons had intermediate clay percentages, with a maximum of 49.6% at Site 5, and a
minimum at Site 4 of 16.6%. There was little variation among sites and depths for mean silt
percentages. None of the horizons analyzed had more than 42.4% of silt. The Ap and C
horizons generally had higher percentages of sand for all sites, with a maximum of 81.2 in the C
horizon at Site 4 (Table 3.1).
These percentages correspond to clay and sandy clay textures described for the Bt
horizon in the field. Considering the whole soil profile, a clay soil texture was observed in the
Bt1 horizons, and either a sandy clay loam or a clay loam texture in lower Bt and BC horizons
(middle depth of Ks measurement). Mean sand, silt, and clay percentages of 59.6, 25.2, and
15.2% respectively were observed for CB and C horizons at the deepest measurement depth. In
general, field textures agreed with data from particle size analysis.
Clay content was a significant parameter from the fitted regression model (P<0.05)
(Table 3.2). When clay content was plotted against Ks values, however, the relationship was
weak with a very low R2 (Fig. 3.2). The Bt horizons generally had the highest clay percentage
and the highest Ks. However a few BC and C horizons also had very high Ks values which were
interpreted to be because of low clay content in these horizons. Thus, because there were two
types of horizons with high Ks those with high clay and moderate structure, and those with low
clay and weak or massive structure, no strong relationship was found between clay content and
Ks. Horizons with intermediate clay content and weak blocky structure generally had low Ks.
50
Bulk density
Shrink-swell behavior of a soil can be best predicted by examining a combination of its
physical, chemical, and mineralogical soil properties. Bulk density varies depending on porosity,
texture, and structure. As shrink-swell potential is the product of the interaction of more than
one characteristic, there is no one method of soil analysis that estimates shrink-swell potential
accurately for all soils. A high dry bulk density is related to a low porosity, which is what occurs
in the BC and upper C horizons in the pedon sampled (means of 1.58 and 1.53 Mg m-3,
respectively). The opposite occurred in Bt and deeper C horizons, where the mean bulk density
was 1.38 Mg m-3. This was interpreted to be related to the presence of subangular blocky
structure in the Bt horizons creating large pores. In C horizons, packing pores between grains
resulted in similar bulk density to Bt horizon.
The moist and dry bulk densities were considered together to determine the COLE. The
relationship between COLE and Ks was negative, and the R2 value was very low (Fig 3.3). The
negative relationship was expected since swelling of a soil horizon would collapse or reduce the
size of large pores, especially those formed by structural units. Moist and dry bulk density, and
COLE were not significant predictors of Ks values when a model was fitted for all sites (Table
3.2). However, in a model of just sites where CEC data were available (sites 1, 2, 3, and 5),
COLE (P<0.05) and moist and dry bulk densities (P<0.01) were all significantly related to Ks
values (Table 3.3).
Cation exchange capacity
Cation exchange capacity varied along the profile and no specific horizon was higher or
lower than the others. Clay activity was determined from the CEC and the clay content of the
51
horizon, dividing the CEC by the percentage of clay. Even though the Bt horizons had relatively
higher clay contents, the clay activity for these horizons was lower than the A and C horizons.
The correlation between CEC and Ks was low, as was the correlation between Ks and clay
activity (Figs. 3.4 and 3.5), and clay activity (CEC/clay) had a very low R2 values (Figs. 3.6).
Conclusions
Given the five sites within the Georgia Piedmont, and considering all the locations within
each site, all the properties studied had a very low relationship with Ks. When comparing all the
properties separately, clay was the property that had the highest correlation with Ks, even though
this value was low. Clay activity had no relationship with Ks.
When parameters were fitted into a regression model, and all sites were considered, clay
was significantly related to Ks values (P<0.05), while bulk density and COLE were not (Table
3.2). When CEC and clay activity were added to the model, for sites 1, 2, 3, and 5, all of the
parameters were significantly related to Ks except for CEC and clay activity (Table 3.3). In
general, no parameter can be used alone to predict Ks. There are many properties that are present
in a soil which can affect its hydraulic properties. The soil needs to be examined as a whole and
the interaction among different properties should be considered.
References
Bouma, J., C. Belmans, L.W. Dekker, and W.J.M. Jeurissen. 1983. Assessing the
suitability of soils with macropores for subsurface liquid waste disposal. J. Environ. Qual.
12:305-311.
Kilmer, V.J., and L.T. Alexander. 1949. Methods of making mechanical analysis of soils. Soil
Sci. 68:15-24.
52
Overbaugh, M.J. 1996. Assessment of the hydraulic properties of a soil-saprolite
sequence near Watkinsville, Georgia, Masters Thesis, Department of Geology, University
of Georgia.
Soil Survey Division Staff, 1993. Soil survey manual. Agric. Handbook 18, USDA-
NRCS. U.S. Government Printing Office, Washington, D.C.
Soil Survey Laboratory Staff. 1996. Soil survey laboratory methods manual. Soil Survey
Investigations Report No. 42, Version 3.0. National Soil Survey Center, Lincoln, NE.
Thomas, P.J., J.C. Baker and L.W. Zelazny. 2000. An expansive soil index for predicting shrink–
swell potential. Soil Sci. Soc. Am. J. 64:268-274.
United States Department of Agriculture. Natural Resources Conservation Service [On line].
Available at <http://www.wmo.ch/web/gcos/terre/variable/slpart.html> (verified 19 July
2004).
53
Table 3.1. Particle size, bulk density, CEC and Ks for selected pedons
Site Pedon Horizon Depth
(cm)
Sand
%
Silt
%
Clay
%
Moist
Bulk d
g cm-3
Dry
Bulk d
g cm-3
COLE CEC
Cmol(+)
Kg-1
Ks
cm
d-1
1 A1 Ap 0 to 8 58.1 32.1 9.7 . . . 15.764 .
BE 8 to 12 . . . . . . . .
Bt1 12 to 30 37.9 14.6 47.5 . . . 11.370 1857
Bt2 30 to 58 18.3 17.0 64.7 1.26 1.38 0.031 12.409 8.0
BC 58 to 83 38.1 27.9 34.0 1.45 1.58 0.027 . .
C1 83 to 119 72.8 15.0 12.2 1.49 1.53 0.008 6.588 .
C2 119 to 140 61.0 23.1 15.9 1.35 1.42 0.016 7.224 2138
C3 140 to 200+ 50.7 34.4 14.9 1.32 1.39 0.016 6.410 .
B3 Ap 0 to 9 70.7 22.9 6.4 . . . 11.968 .
AE 9 to 23 76.2 6.9 16.9 . . . 7.932 .
BE 23 to 32 63.8 21.2 15.0 . . . 5.637 .
Bt1 32 to 56 33.2 13.3 53.5 1.36 1.41 0.011 28.619 2.6
Bt2 56 to 79 40.5 12.3 47.2 1.35 1.47 0.028 26.337 7.0
BC 79 to 107 55.7 17.1 27.2 1.57 1.63 0.014 5.241 .
CB 107 to 146 57.4 17.8 24.8 1.61 1.65 0.007 16.558 5.7
C 146 to 200+ 70.6 16.6 12.8 1.55 1.59 0.009 6.456 .
G2 Ap 0 to 7 60.8 24.1 15.0 . . . 14.384 .
Fill 7 to 35 47.5 20.7 31.8 . . . 25.146 .
Bt1 35 to 65 38.2 16.6 45.2 1.47 1.56 0.019 29.379 1693
BC1 65 to 98 39.3 17.0 43.7 1.46 1.62 0.035 . 1.3
BC2 98 to 142 36.4 23.0 40.7 1.32 1.45 0.033 . 1.3
C 142 to 200+ 49.6 28.3 22.1 1.42 1.53 0.024 25.271 .
54
Site Pedon Horizon Depth
(cm)
Sand
%
Silt
%
Clay
%
Moist
Bulk d.
g cm-3
Dry
Bulk d.
g cm-3
COLE CEC
Cmol(+)
Kg-1
Ks
cm
d-1
2 B2 Ap 0 to 21 49.6 34.6 15.7 . . . 12.277 .
BA 21 to 40 38.3 36.5 25.1 1.37 1.54 0.040 16.308 .
Bt1 40 to 84 39.7 26.6 33.7 1.51 1.66 0.031 24.623 25.6
Bt2 84 to 105 47.5 20.8 31.7 1.51 1.68 0.035 24.041 .
BCt1 105 to 137 47.0 22.9 30.1 1.55 1.77 0.043 . 14.4
BCt2 137 to 150 32.4 34.7 32.8 1.62 1.75 0.025 24.425 15.1
E1 Ap 0 to 5 58.2 25.3 16.4 . . . 8.223 .
AB 5 to 13 53.1 23.2 23.7 . . . 7.205 .
Bt1 13 to 48 29.3 24.7 45.9 1.57 1.70 0.026 12.066 1.5
Bt2 48 to 84 34.8 29.1 36.1 1.39 1.55 0.036 11.223 2.3
BCt1 84 to 114 37.8 28.7 33.4 1.36 1.56 0.047 9.999 .
BCt2 114 to 150 40.5 31.2 28.3 1.31 1.48 0.041 7.932 4.5
C 150 to 180 49.5 26.1 24.5 1.31 1.51 0.048 7.114 .
G1 Ap 0 to 16 45.1 41.6 13.3 . . . 23.671 .
BA 16 to 32 44.5 39.1 16.4 . . . 24.037 .
Bt1 32 to 67 34.4 41.7 23.9 1.52 1.67 0.033 24.298 16.5
Bt2 67 to 102 34.2 22.4 43.4 1.42 1.58 0.036 26.600 6.6
BCt1 102 to 141 39.1 26.5 34.4 1.43 1.52 0.021 24.705 2.3
BCt2 141 to 180 39.2 8.4 52.4 1.40 1.47 0.017 26.206 .
55
Site Pedon Horizon Depth
(cm)
Sand
%
Silt
%
Clay
%
Moist
Bulk d.
g cm-3
Dry
Bulk
density
g cm-3
COLE CEC
Cmol(+)
Kg-1
Ks
cm d-1
3 A1 A 0 to 20 73.0 18.4 8.6 1.70 1.77 0.012 20.686 .
Bt 20 to 82 29.4 17.6 53.0 1.24 1.40 0.040 21.802 15.3
BCt (sapr.) 82 to 133 51.6 26.2 22.2 1.38 1.51 0.030 22.590 0.3
BCt 82 to 133 42.1 25.5 32.4 1.38 1.51 0.030 22.590 .
CB 133 to 170 46.3 24.2 29.5 1.41 1.52 0.025 . 1.5
C 170 to 200 45.3 34.1 20.6 1.39 1.52 0.029 . .
C3 Ap 0 to 4 41.3 37.7 21.0 . . . 17.387 .
Bt1 4 to 13 44.7 20.9 34.4 1.60 1.75 0.029 17.093 11.1
Bt2 13 to 50 37.6 18.1 44.3 1.36 1.51 0.035 . .
BCt1 50 to 71 55.5 19.4 25.1 1.48 1.59 0.023 . 0.7
BCt2 71 to 124 53.5 17.2 29.3 1.44 1.60 0.035 . .
C/B (B part) 124 to 173 58.0 28.8 13.2 1.39 1.48 0.022 18.549 1467
C/B (C part) 124 to 173 70.8 21.7 7.5 1.48 1.55 0.014 0.610 .
C 173 to 200 . . . 1.24 1.29 0.013 2.159 .
G3 Ap 0 to 5 . . . . . . . .
BA 5 to 27 . . . 1.66 1.77 0.021 25.512 .
Bt 27 to 68 . . . 1.40 1.53 0.030 . 1791
BCt 68 to 105 . . . 1.31 1.41 0.025 22.823 0.2
BC 105 to 136 . . . 1.50 1.60 0.021 22.034 10.3
C 136 to 200 . . . 1.32 1.37 0.010
22.116
.
56
Site Pedon Horizon Depth
(cm)
Sand
%
Silt
%
Clay
%
Moist
Bulk d.
g cm-3
Dry
Bulk d.
g cm-3
COLE CEC
Cmol(+)
Kg-1
Ks
cm
d-1
4 C1 Ap1 0 to 7 56.2 20.4 23.4 . . . . .
Ap2 7 to 18 53.6 19.9 26.5 . . . . .
Bw1 18 to 37 64.6 13.2 22.2 1.41 1.46 0.009 . 42.9
Bw2 37 to 62 71.4 10.6 17.9 1.40 1.45 0.009 . .
Bw3 62 to 137 66.5 13.8 19.6 1.25 1.30 0.014 . 12.0
CB 137 to 150 72.6 15.1 12.4 1.27 1.41 0.036 . 380
D3 Ap 0 to 15 45.6 25.5 28.9 . . . . .
Bt1 15 to 27 19.3 13.4 67.3 1.20 1.22 0.003 . 331.6
Bt2 27 to 45 31.5 11.9 56.6 1.24 1.32 0.022 . .
2BC1 45 to 79 49.6 24.9 25.6 1.47 1.47 0 . 6.0
2BC2 79 to 101 63.8 11.8 24.4 1.31 1.41 0.025 . .
2C1 101 to 132 81.2 15.1 3.7 1.69 1.70 0.003 . .
2C2 132 to 153 63.6 16.6 19.8 1.13 1.43 0.106 . 34.2
G1 Ap 0 to 15 41.5 32.0 26.4 . . . . .
Bt1 15 to 34 22.7 26.5 50.8 1.45 1.51 0.012 . 11.4
Bt2 34 to 56 27.5 31.6 40.9 1.40 1.40 0 . 10.0
BC1 56 to 76 35.0 37.7 27.3 1.15 1.20 0.014 . .
BC2 76 to 127 41.0 42.4 16.6 1.19 1.22 0.006 . .
C1 127 to 158 59.0 32.2 8.8 1.17 1.23 0.016 . 1.9
C2 158 to 175+ 56.4 36.0 7.6 1.15 1.23 0.022 . .
57
Site Pedon Horizon Depth
(cm)
Sand Silt Clay Moist
Bulk d.
g cm-3
Dry
Bulk d.
g cm-3
COLE CEC
Cmol(+)
Kg-1
Ks
cm
d-1
5 C2 Ap 0 to 7 44.1 14.9 41.1 . . . . .
Bt1 7 to 23 . . . . . . . 7.0
Bt2 23 to 50 . . . . . . . .
BCt1 50 to 72 . . . . . . . 3.8
C/BCt 72 to 111 . . . . . . . .
C/Cr 111 to 145 . . . . . . . 101.9
Cr 145 to 146+ . . . . . . . .
D3 Ap 0 to 12 56.6 29.6 13.8 . . . 11.288 .
Bt1 12 to 47 35.8 16.9 47.3 1.34 1.36 0.003 14.049 312
Bt2 47 to 84 44.1 14.9 41.1 1.28 1.28 0 13.406 .
BCt 84 to 119 . . . 1.22 1.22 0 . 42.9
BCt/C 119 to 157 . . . 1.30 1.31 0.003 . 5.0
C/BC 157 to 180+ . . . 0.80 1.22 0.211 . .
G3 Ap 0 to 7 44.5 29.7 25.8 . . . 14.286 .
Bt1 7 to 24 26.7 15.2 58.1 1.35 1.42 0.018 12.231 31.6
Bt2 24 to 66 31.0 12.5 56.5 1.34 1.34 0 13.242 .
BCt1 66 to 93 36.9 13.6 49.6 1.32 1.32 0 9.616 8.0
BCt2 93 to 128 46.2 7.8 46.0 1.28 1.28 0 9.134 .
BCt3 128 to 170+ 50.4 8.5 41.2 1.45 1.47 0.003 12.292
3.8
58
Table 3.2. Analysis of variance of Ks data for all sites as affected by moist and dry bulk density,
COLE, and clay content.
Source DF P-value‡
Model 8 **
Site 4 **
Moist bulk density 1 NS
Dry bulk density 1 NS
COLE 1 NS
Clay content 1 *
Error 58
‡ P-values < 0.1=†, < 0.05=*, < 0.01=**, < 0.001=***
Table 3.3. Analysis of variance of Ks data for sites 1, 2, 3, and 5 as affected by moist and dry
bulk density, COLE, clay content, CEC, and clay activity.
Source DF P-value‡
Model 9 **
Site 2 *
Moist bulk density 1 †
Dry bulk density 1 †
COLE 1 †
Clay content 1 *
CEC 1 NS
Clay activity 1 NS
Error 32
‡ P-values < 0.1=†, < 0.05=*, < 0.01=**, < 0.001=***
59
Figure 3.1. Mean percentage (%) of clay, silt and sand by depth for all sites.
Horizon
Ap BA Bt BC C
Part
icle
siz
e pe
rcen
tage
0
10
20
30
40
50
60
70ClaySiltSand
60
Figure 3.2. Relationship between Ks and clay.
Clay0 20 40 60 80
Ks
(cm
d-1
)
-500
0
500
1000
1500
2000
2500R2 = 0.0663
61
Figure 3.3. Relationship between Ks and COLE.
COLE0.00 0.05 0.10 0.15 0.20 0.25
Ks
(cm
d-1
)
-500
0
500
1000
1500
2000
2500R2 = 0.0108
62
Figure 3.4. Relationship between Ks and CEC.
CEC Cmol (+) Kg soil-10 10 20 30
Ks
(cm
d-1
)
0
500
1000
1500
2000
2500R2 = 0.0650
63
Figure 3.5. Relationship between Ks and clay activity.
0 1 2 3 4
Ks
(cm
d-1
)
0
500
1000
1500
2000
2500R2 = 0.000
Clay activity(CEC Mg m3/clay%)
64
CONCLUSIONS AND IMPLICATIONS
Permeability is often estimated in the field or taken from soil survey databases. A
combination of properties, such as texture, clay mineralogy, bulk density, and cementation,
determines the Ks of a soil. Aggregation or pedogenic structure is a predominant component for
estimating hydraulic parameters. It has an apparent great impact on permeability because of the
network of macropores formed between peds.
For soils in the Georgia Piedmont, upper Bt horizons had a high clay content, well
developed structure, and the highest Ks within the profile. Structure in these horizons forms a
network of large pores that is capable of rapid transmittal of water through these horizons. The
lower Bt and BC horizons had lower Ks than upper Bt at most sites. There horizons had lower
clay contents than the overlying upper Bt horizons, but because these horizons were weakly
structured, the macropore network present in the upper Bt horizons was absent and rates of water
movement were lower. For most of the deeper BC and CB horizons , Ks was similar to values
observed in lower Bt horizons even though clay content was lower which is also attributed to
weakly developed structure.. The C horizons in the pedons sampled had the lowest clay content
were massive. However, Ks of these horizons was, in many cases similar to those of upper Bt
horizons. Apparently the clay content in these C horizons was less than a threshold necessary to
clog pores between sand grains, and these horizons have rapid water movement through coarse
packing pores.
Laboratory analyses examined the relationships between Ks and properties of the
horizons evaluated. It was complimentary to the field data and together, both permitted better
understanding of the permeability of soils in the Georgia Piedmont. Clay content was a
significant property for a regression model for predicting Ks, but the R2 for this model was low.
65
When evaluated as a single variable, the relationship between Ks and clay was very weak. None
of the other properties evaluated (moist and dry bulk density, COLE, CEC, and clay activity,
were significant in the model). The lack of strong correlation between these properties and Ks
supports the interpretation that pedogenic structure has a major influence on water movement
rates in these soils.
66
Appendix 1.1. Mean Ks for hillslope by depth at Sites 1 and 2.
Site Hillslope† Depth‡
Ks
(cm d-1)
Site Hillslope† Depth‡
Ks
(cm d-1)
1 A S 1586 2 A S 18
M 14 M 3
D 723 D 1
B S 932 B S 10
M 7 M 7
D 852 D 5
C S 1329 C S 16
M 26 M 3
D 546 D 4
D S 2099 D S 4
M 5 M 5
D 8 D 2
E S 1648 E S 2
M 16 M 2
D 15 D 2
F S 1762 F S 5
M 7 M 3
D 17 D 1
G S 1791 G S 6
M 5 M 3
D 5 D 4
† letters indicate landscape position from summit to footslope, A to G. ‡ S = shallow; M = middle; D = deep
67
Appendix 1.2. Mean Ks for hillslope by depth at Sites 3 and 4.
Site Hillslope† Depth‡
Ks
(cm d-1)
Site Hillslope† Depth‡
Ks
(cm d-1)
3 A S 13 4 A S 30
M 0 M 13
D 2 D 103
B S 8 B S 82
M 0 M 28
D 1 D 32
C S 8 C S 62
M 0 M 13
D 492 D 150
D S 644 D S 121
M 1 M 4
D 493 D 58
E S 468 E S 82
M 2 M 11
D 10 D 48
F S 1542 F S 220
M 2 M 12
D 6 D 31
G S 1792 G S 22
M 7 M 7
D 9 D 10
† letters indicate landscape position from summit to footslope, A to G. ‡ S = shallow; M = middle; D = deep
68
Appendix 1.3. Mean Ks for hillslope by depth at Site 5.
Site Hillslope† Depth‡
Ks
(cm d-1)
5 A S 17
M 5
D 9
B S 67
M 7
D 7
C S 18
M 7
D 45
D S 116
M 23
D 64
E S 130
M 8
D 14
F S 20
M 6
D 32
G S 21
M 6
D 2
† letters indicate landscape position from summit to footslope, A to G. The numbers correspond to the transect. ‡ S = shallow; M = middle; D = deep
69
Appendix 1.4. Morphological features of pits at Site 1.
Site Hillslope† Horizon Depth Structure‡ Texture§ Munsell color
1 A1 Ap 0 to 8 2 f gr sl 2.5 YR 3/3
BE 8 to 12 1 f sbk scl 5 YR 4/6
Bt1 12 to 30 2 m sbk c 2.5 YR 4/6
Bt2 30 to 58 3 m sbk, m pr c 2.5 YR 4/8
BC 58 to 83 1 m sbk scl 2.5 YR 4/8
C1 83 to 119 Ma cosl 5 YR 5/8
C2 119 to 140 Ma sl 2.5 YR 4/8
C3 140 to 200+ Ma scl 2.5 YR 4/8
B3 Ap 0 to 9 2 f gr Sl 10 YR 3/3
AE 9 to 23 1 f sbk Sl 10 YR 4/6
BE 23 to 32 1 f sbk Scl 7.5 YR 4/6
Bt1 32 to 56 2 m sbk C 2.5 YR 4/6
Bt2 56 to 79 2 m sbk Sc 2.5 YR 4/6
BC 79 to 107 1 m sbk Scl 2.5 YR 4/8
CB 107 to 146 1 m sbk Scl 10 YR 4/8
C 146 to 200+ Ma Sl 5 YR 5/8
G2 Ap 0 to 7 2 f gr Sl 10 YR 3/4
fill 7 to 35 1 f sbk Scl 5 YR 4/6
Bt1 35 to 65 2 m pl C 5 YR 4/6
BC1 65 to 98 Very 1 m sbk Scl 10 R 4/6
BC2 98 to 142 Very 1 m sbk Scl 10 R 4/6
C 142 to 200+ Ma Scl 5 YR 4/6
† letters indicate landscape position from summit to footslope, A to G. The numbers correspond to the transect. ‡ Gr=granular; Sbk=subangular blocky; Abk=angular blocky; Ma=massive; 1=weak; 2=moderate; 3=strong; f=fine;
m=medium; c=coarse; vc=very coarse; pr=prismatic; pl=platy. § C=clay; Sl=Sandy loam; Sc=Sandy clay; Sl=Sandy loam; L=loam; Scl=Sandy clay loam; Cos=coarse;
sapr=saprolite.
70
Appendix 1.5. Morphological features of pits at Site 2.
Site Hillslope† Horizon Depth Structure‡ Texture§ Munsell color
2 B2 Ap 0 to 21 2 m gr Sl 5 YR 3/3
BA 21 to 40 1 m sbk L 5 YR 3/4
Bt1 40 to 84 2 m abk C 2.5 YR 4/4
Bt2 84 to 105 2 c abk C 2.5 YR 4/4
BCt1 105 to 137 2 f abk Cl 2.5 YR 4/6
BCt2 137 to 150 2 f abk Cl 2.5 YR 4/8
E1 Ap 0 to 5 2 m gr Sl 5 YR 4/4
BA 5 to 13 1 m sbk Sl 5 YR 4/6
Bt 13 to 104 2 c abk, pr C 2.5 YR 4/6
BCt 104 to 150 1 c abk Cl 2.5 YR 5/6
C 150 to 180 Ma L 5 YR 5/6
G1 Ap 0 to 16 2 f gr Sl 7.5 YR 4/2
BA 16 to 32 1 m sbk Scl 5 YR 4/4
Bt 32 to 102 3 c sbk, pr C 2.5 YR 4/6
BCt 102 to 180 2 m sbk Cl 60% 5YR 5/6
40% 10R 4/6
† letters indicate landscape position from summit to footslope, A to G. The numbers correspond to the transect. ‡ Gr=granular; Sbk=subangular blocky; Abk=angular blocky; Ma=massive; 1=weak; 2=moderate; 3=strong; f=fine;
m=medium; c=coarse; vc=very coarse; pr=prismatic; pl=platy. § C=clay; Sl=Sandy loam; Sc=Sandy clay; Sl=Sandy loam; L=loam; Scl=Sandy clay loam; Cos=coarse;
sapr=saprolite.
71
Appendix 1.6. Morphological features of pits at Site 3.
Site Hillslope† Horizon Depth Structure‡ Texture§ Munsell color
3 A1 A1 0 to 7 2 m gr Sl 5 YR 4/3
A2 7 to 20 2 m gr Sl 5 YR 5/4
Bt 20 to 82 2 mnc sbk C 10 R 4/6
BCt 82 to 133 1 c sbk Cl 10 R 4/6
CB 133 to 170 1 m sbk L 2.5 YR 5/6, 10 R 4/6
C 170 to 200 Ma L 10 R 4/4
C3 Ap 0 to 4.5 1 m gr L 2.5 YR 3/3
Bt1 4.5 to 13 2 f sbk Cl 10 R 4/4
Bt2 13 to 50 2 m sbk C 10 R 4/6
BCt1 50 to 71 1 m abk, ma L, sl sapr. 10 R 4/6, multicolor
BCt2 71 to 124 1 m abk, ma L, sl sapr. 10 R 4/6, multicolor
C/B 124 to 173 1 c abk, ma L, sl sapr. 10 R 4/4, multicolor
C 173 to 200 Ma Sl sapr. Multicolor
G3 Ap 0 to 5 2 f gr L 5 YR 4/3
BA 5 to 27 1 c sbk Scl 2.5 YR 4/4
Bt 27 to 68 2 m sbk C 10 R 4/6
BCt 68 to 105 2 c sbk Cl 10 R 4/6
BC 105 to 136 1 c sbk, ma Scl, cl sapr. 10 R 4/6, multicolor
C 136 to 200 Ma Sl sapr. 10 R 6/3
† letters indicate landscape position from summit to footslope, A to G. The numbers correspond to the transect. ‡ Gr=granular; Sbk=subangular blocky; Abk=angular blocky; Ma=massive; 1=weak; 2=moderate; 3=strong; f=fine;
m=medium; c=coarse; vc=very coarse; pr=prismatic; pl=platy. § C=clay; Sl=Sandy loam; Sc=Sandy clay; Sl=Sandy loam; L=loam; Scl=Sandy clay loam; Cos=coarse;
sapr=saprolite.
72
Appendix 1.7. Morphological features of pits at Site 4.
Site Hillslope† Horizon Depth Structure‡ Texture§ Munsell color
4 C1 Ap1 0 to 7 2 m gr Sl 7.5 YR 3/3
Ap2 7 to 18 2 m gr Sl 5 YR 4/4
Bw1 18 to 37 1 f sbk Scl 2.5 YR 4/6
Bw2 37 to 62 1 f sbk Ls 2.5 YR 4/6
Bw3 62 to 137 1 f sbk Ls 2.5 YR 4/6
CB 137 to 150 Ma Sl 2.5 YR 4/6, 10 YR 3/1
D3 Ap 0 to 15 2 vc sbk Cl 2.5 YR 3/6
Bt1 15 to 27 2 m sbk C 2.5 YR 3/6
Bt2 27 to 45 1, 2 m sbk Cl 2.5 YR 3/6
2BC1 45 to 79 1 m sbk Sl 2.5 YR 3/6
2BC2 79 to 101 1 m sbk Sl 2.5 YR 3/6
2C1 101 to 132 Ma Sl 2.5 YR 3/6, multicolor
2C2 132 to 153 Ma Sl 10 R 3/6
Cr 153 to 165+ Ma Weathered gneiss
G1 Ap 0 to 15 2 f gr, sbk Scl 5 YR 4/4
Bt1 15 to 34 2 m sbk C 2.5 YR 4/6
Bt2 34 to 56 2 m sbk Cl 2.5 YR 4/6
BC1 56 to 76 1 f sbk Scl 2,5 YR 4/6
BC2 76 to 127 1 m sbk Sl 2.5 YR 4/6
C1 127 to 158 Ma Sl 10 R 4/6
C2 158 to 175+ Ma Sl 2.5 YR 4/6
† letters indicate landscape position from summit to footslope, A to G. The numbers correspond to the transect. ‡ Gr=granular; Sbk=subangular blocky; Abk=angular blocky; Ma=massive; 1=weak; 2=moderate; 3=strong; f=fine;
m=medium; c=coarse; vc=very coarse; pr=prismatic; pl=platy. § C=clay; Sl=Sandy loam; Sc=Sandy clay; Sl=Sandy loam; L=loam; Scl=Sandy clay loam; Cos=coarse;
sapr=saprolite.
73
Appendix 1.8. Morphological features of pits at Site 5.
Site Hillslope† Horizon Depth Structure‡ Texture§ Munsell color
5 C2 Ap 0 to 7 2 m gr, sbk Cl 2.5 YR 3/4
Bt1 7 to 23 2 m sbk Cl 2.5 YR 3/6
Bt2 23 to 50 1 m sbk Cl 2.5 YR 4/6
BCt1 50 to 72 1 m sbk L 2.5 YR 4/6
C/BCt 72 to 111 1 m sbk L 2.5 YR 4/8
C/Cr 111 to 145 Ma Sl 2.5 YR 4/6
Cr 145 to 146+ Ma
D3 Ap 0 to 12 2 f gr, sbk Scl 7.5 YR 3/3
Bt1 12 to 47 2, 3 f sbk Cl 10 R 3/4
Bt2 47 to 84 2 f sbk Scl 10 R 3/4
BCt1 84 to 119 1 m sbk L 2.5 YR 4/6
BCt/C 119 to 157 Very 1 m sbk Sl 2.5 YR 4/6
C/BC 157 to 180+ Very 1 m sbk Cosl 2.5 YR 4/6
G3 Ap 0 to 7 1 f gr Scl 5 YR 3/4
Bt1 7 to 24 1, 2 f sbk Cl 2.5 YR 3/6
Bt2 24 to 66 1, 2 f sbk Cl 10 R 4/6
BCt1 66 to 93 1 m sbk L 10 R 4/6
BCt2 93 to 128 1 f sbk L 10 R 4/6
BCt3 128 to 170+ 1 f sbk Sl 10 R 4/6
† letters indicate landscape position from summit to footslope, A to G. The numbers correspond to the transect. ‡ Gr=granular; Sbk=subangular blocky; Abk=angular blocky; Ma=massive; 1=weak; 2=moderate; 3=strong; f=fine;
m=medium; c=coarse; vc=very coarse; pr=prismatic; pl=platy. § C=clay; Sl=Sandy loam; Sc=Sandy clay; Sl=Sandy loam; L=loam; Scl=Sandy clay loam; Cos=coarse;
sapr=saprolite.