evaluation of permeability estimates for soils in the

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


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


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 2.4: Distribution of Ks by depth at site 4.................................….......................................35


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-


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.



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.



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.



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.



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.


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


Shallow Middle Deep

Ks

(cm

d- 1

)

0

2

4

6

8

10a

abb

34


Shallow Middle Deep

Ks

(cm

d-1

)

0

100

200

300

400

500

600

700a

ab

b

35


Shallow Middle Deep

Ks

(cm

d- 1

)

0

20

40

60

80

100a

ab

b

36


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


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


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



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 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


(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


(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


(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


(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.


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.


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)


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.


Ks

(cm d-1)


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.


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



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



sapr=saprolite.

71



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



sapr=saprolite.

72



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



sapr=saprolite.

73



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



sapr=saprolite.

evaluation of permeability estimates for soils in the

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