Soils of Native Prairie Remnants
in the Jackson Prairie Region
of Mississippi

Published by the Office of Agricultural Communications, Division of Agriculture, Forestry, and Veterinary Medicine, Mississippi State University. Edited by Keith H. Remy, Senior Publications Editor.

Acknowledgments

Gratitude is extended to Ken Gordon, Mississippi Museum of National Science, and U.S. Forest Service personnel of the Bienville National Forest for their cooperation and encouragement in this study. We gratefully acknowledge the assistance of J. E. Autry, National Resources Conservation Service.

Special thanks are extended to Keith Remy for his guidance and critical review of the paper. We gratefully acknowledge the reviews and suggestions of Lamar Kimbrough, David Lang, Glover Triplett, and Robert Wimbish.

Table of Contents

• Acknowledgments
• Abstract
• Introduction
• Physical Setting of the Jackson Prairie Region

  Climate and Geology

  Soils of Prairie Openings

• Disturbance, Use, and Management of the Prairies
• Early Writings about the Prairies
• Materials and Methods

  Study Sites

  Laboratory Analysis

• Results and Discussion

  Morphology

  Physical Properties

  Chemical Properties

• Conclusions
• References Cited

List of Tables

1. Soil classification of the prairie remnants
2. Morphology of the pedons at Durand Oak Prairie and Harrell Prairie Hill
3. Morphology of the pedons of Five-Acre Prairie and Eureka Church Prairie
4. Physical properties for selected soil horizons in the prairie pedons
5. Selected chemical properties of the prairie pedons

Abstract

Prairie remnants in the Jackson Prairie Region of Mississippi occur as calcareous islands of gently sloping uplands surrounded by acid soils with pine and hardwood forests. Soils of four prairie remnants were examined and sampled in excavated pits for characterization. The soils (Chromic Hapluderts) are clayey and calcareous with high shrink-swell potentials and high cation exchange capacities. The soils formed in Yazoo Clay of Eocene Age and exhibit little weathering. The calcium-rich soils have ochric epipedons with organic matter contents of 4 to 6% and exhibit evidence of accelerated erosion. Mollic epipedons occur in areas lacking erosion. Subsoils have cambic horizons, compound structure and intersecting slickensides. Surface cracks extend to depths of 3 feet or greater during dry summer months.

Introduction

Prairie remnants are being discovered and studied in the Blackland Prairie regions of Mississippi. The Jackson Prairie Belt and the Black Prairie Belt are two physiographic regions in Mississippi containing prairies; both are known as the Blackland Prairies. Presently, more than 54 prairie sites in the Jackson Prairie Belt have been located and described by the Natural Heritage Program (Wieland, 1991).

The prairie remnants occur as isolated calcareous islands of various sizes surrounded by acid mixed pine and hardwood forests (Moran, 1995). The islands range in size from <1 to 160 acres and total about 802 acres (Wieland and Gordon, 1991). Composites (21%), legumes (12%), and graminoids (15%) make up the floral composition in the prairie remnants (Wieland and Gordon, 1991). Species are currently maintained by the application of special management programs, such as controlled burning (Wieland, 1991). A post oak acid prairie occurs where the lowlands are acid and forested with pines and oak-hickory trees, while grasslands cover the steep, alkaline shallow ridges and outcrops (Peacock, 1992; Wieland and Weeks, 1990).

The objectives of this study were to (1) characterize the soils of representative areas identified as vestige prairies in the Jackson Prairie Belt; and (2) determine the current impact of accelerated erosion induced by cultural disturbance in these vestige prairie soils.

Physical Setting of Jackson Prairie Region

Climate and Geology

The bathyal sedimentary clayey materials of the Yazoo Clay Formation were deposited in a neritic or deep marine environment of the Mississippi embayment. In addition, significant beds of shallow-water fauna and materials were deposited periodically because of small-scale gravity flow and occasional dramatic turbidity flow progressing from adjacent uplands and shallower coastal seas (Smith and Zumwalt, 1987). Earlier, Yazoo sea oyster reefs extended over large areas. At this time and later, the bones of the large whale-like mammal, Zeuglodon, settled into the muds (Bergquist and McCutcheon, 1942). The fossil taxa, Zeuglodon, found associated to these sites, is presently recognized as two separate species, Basilosaurus setoides and Zygorhiza kochii (Daly, Personal communication). Fossil oysters, prehistoric whales, and other calcareous sediments are normally found in proximity to Yazoo clay outcrops, and provide abundant calcium cations, which are essential for the formation of alkaline soils on the prairies.

One of ten topographic regions of the State of Mississippi (Lowe, 1921), the Jackson Prairie Belt extends across central Mississippi from the edge of the Loess Bluff Region at Yazoo City to the eastern border between Alabama and Mississippi, and continues for a short distance into Washington County, Alabama (Moore, 1969) (See Figure 1).

In the Gulf Coast stratigraphy, the Eocene Epoch is divided into Wilcox, Claiborne, and Jackson Stages. The Jackson Stage is a time-rock unit approximately 38 million years old, whereas the Jackson Group refers to the rock unit (Schiebout, 1986). The Jackson Group is the uppermost rock of the epoch, partly consisting of a lower Moody's Branch Formation and upper Yazoo Clay Formation. The Yazoo clay is composed of green and gray calcareous clays containing some sand and marl; the Moody's Branch Formation at its base is a mixture of shells embedded in glauconitic clayey quartz sand (Moore, 1969).

In a topo-geologic classification (Hodgkins, Golden, and Miller, 1979), the region lies within the Hilly Coastal Plain Province and is subdivided into the Jackson Hills Region and Jackson Prairie Region. The Jackson Hills Region, which is substantially covered with pine forest, is a "ruggedly hilly divide, of deep sandy and loamy soils, extending throughout much of the length of the Jackson Prairie." The Jackson Prairie Region, according to Hodgkins, Golden, and Miller (1979), is the portion of the region not buried under the sandy Jackson Hills. It consists of gently rolling topography in which land clearing is extensive.

Soils of the Prairies

The major soil order occurring on midwest prairies is Mollisols. The major pedogenic process in Mollisols is melanization, which is the darkening of the soil surface by the accumulation of organic matter. Prairie soils are considered fine-textured, productive, and fertile because of the abundant weatherable minerals and organic matter that serve as plant nutrient reserves.

The dominant epipedon (surface horizon) associated with Mollisols is the mollic epipedon. The mollic epipedon contains 1% or more organic matter with color values darker than 3.5 when moist, color chromas less than 3.5 when moist, base saturations greater than 50%, and no hard to extremely hard consistency when dry to a depth of 7 inches (Soil Survey Staff, 1996).

The surface horizon (A) in midwest prairie soils is commonly about 18 inches thick and has granular structure due to repeated freezing-thawing, wetting-drying, humus accumulation, and the influence of the root system (Weaver, 1968). The subsoil (B horizons) is generally thick, with clay contents nearly equal those of the A horizon (Buol et al., 1989).

Disturbance, Use, and Management of the Prairies

Settlement and intense cultivation of the Blackland Prairies have severely impacted the soils and vegetation during the past 200 years. Archeological and ecological studies indicate extensive erosion occurred in these regions after European settlement (Peacock, 1992, 1993). Currently, a large portion of the region is forested and contains more exotic plant species than the past. Recognition of the remaining native prairies and characterization of their soils are critical for successful preservation, long-term integrity, and maximum biological diversity. The nature of soil structure, horizonation, and topography are fundamental soil properties to be considered for successful preservation (Frost et al., 1986).

With large portions of the Jackson Prairie Region being gently rolling and the soils black and relatively fertile, the region attracted early settlement and agricultural development. Settlement occurred more rapidly in counties with prairie soils than in the pine country of southern Mississippi (Hickman, 1962). Hilgard (1860) promoted the settlement of the region by indicating the fertility of calcareous marl soils and their identification as "black prairie" soils.

Excerpts from Hilgard (1860) suggested early settlement of the area and the cultivation and grazing of the "prairie" soils. Fossil bones of the Zeuglodon, which are only found associated with the prairie soils of the Jackson Prairie Region, "are so frequently laid bare by the plow." Patches of true, black prairie soil, found on hilltops and hillsides are "a fine productive soil, but draughty and exceedingly hard to till." The prairie soil is "not always heavy naturally, but sometimes quite mellow and easily tilled, and always very productive of corn." The upland prairies were praised for their cropping potential; however, "wherever the heavy, bluish or yellowish matrix of the Zeuglodon bones" was close to the soil surface within the plow zone, as on the bald prairie, the cotton frequently showed a disposition to rust.

Land uses, including cultivation, grazing, haying, pine tree planting, vehicular traffic, log storage, wildlife food plots, and shell mining (Brown, 1894), have impacted the prairies. On hilly areas, the sequence of logging, cultivation, and subsequent abandonment resulted in deep erosional scars (Bergquist and McCutcheon, 1942). Even though cultivation or other disturbances generally have not occurred on the prairies of the Bienville National Forest for 50 years, many gullies are still evident today.

In the 1930's, the Bienville National Forest was formed to reestablish forests on extensive cutover areas of central Mississippi by planting trees and controlling wildfires. Pine trees that were planted in many openings either died or failed to mature. According to a review by Dale et al. (1955), it is apparent that lime-induced chlorosis is a physiological disease of native pine trees on these types of soils. The degenerative growth of pine on the sites may be caused by improper utilization of iron within the plant, and is exacerbated by soils with fine texture, periodic high moisture content, and poor aeration, all of which aid in inactivating iron within the plant (Thorne et al., 1951).

The relations of mycorrhizae to preventing chlorosis are not clear, but White (1941) and Dale et al. (1955) noted that in a controlled experiment, on highly calcaric soils, short-term nutrition and growth were normal in soils inoculated with mycorrhizae.

Fire suppression contributed to the size reduction of prairie openings by allowing the encroachment of woody vegetation. Generally indicating the rate of encroachment, several comparisons of aerial photos have been made in the Bienville National Forest for the period between 1936 and present day (Dean Elsen, Personal communication).

For Compartment 71, the cumulative size of open prairie was 195 acres in 1936, 59 acres in 1974, but only 34 acres in 1989, an 82% decrease in size over a 50-year period. Total prairie area of Compartment 70 shrank from 71 acres in 1936 to one-third of its size by 1988. The land use history of these areas prior to the 1930's is unknown.

Increasing the prescribed burn frequency by the U.S. Forest Service, Bienville National Forest, from no fires in the 1960's to 0.5, 1.6, and 2.9 fires per prairie per decade during the 1970's, 1980's, and 1990's, respectively, has helped maintain and invigorate many species of the prairie openings (Wieland et al., 1991).

Early Writings About the Prairies

Conducted in the 1830's, the General Land Survey recorded land plots of section, township, and range. Anecdotes about the landscape observed along the survey line were also reported. For one area, it was noted that "rolling prairie with scattered pine and crabapple thickets" occurred along one of their survey lines. The location referred to in the General Land Survey notes is presently known as Harrell Prairie Hill Botanical Area, the largest known prairie of the Jackson Prairie Region (Gordon and Wiseman, 1989). Monette (1851) reported on the existence of prairies, "about 50 miles east of Jackson," on the divide between major drainages of central Mississippi.

Hilgard (1860) recognized that several different types of prairie existed in the Jackson Prairie Region. Though mainly focusing on pedological, geological, or agricultural issues, Hilgard also provided brief accounts of presettlement vegetation and its association to soils. Especially concerning the liminess of the soils as related to agriculture potential, Hilgard recognized native vegetation as a good indicator of soil type.

The calcareous, black soils of the Jackson Prairie Region were termed prairie soils. An area designated as "prairie" was related to the black color of the soils, as with "black prairie." They occurred in the "more hilly portions of the region, confined to the slopes and bottoms of the streams." For a forested site, Hilgard stated, "This analysis seems to exhibit characteristically the prominent features of the black prairie soil of the Tertiary: it is highly retentive of moisture; rich in vegetable matter, in lime, and in all the other essential nutritive ingredients of plants--with the exception, in this instance, of Soda, which seems to be deficient."

Furthermore, in describing the Black Belt Prairie Region of Alabama, Mohr (1901) stated that the term "prairie region" referred less to the "timberless tracts which originally formed a small fraction of its area than to the black, calcareous, highly fertile soil of these uplands, ...[which] closely resembles the equally productive soil of the western treeless prairies."

The black prairie soil was often identified to occur on a site by the vegetation found growing there:

"The true distinguishing features of limy ("calcareous") soils, which never fail to characterize them plainly enough, may be found in the peculiar growth, large and small, which they bear. Chemical reagents cannot more surely announce the presence, in the soil, of a large supply of lime than does the prevalence of the Crab Apple, the Wild Plum, the Cottonwood, the Sycamore, the "Popular," and some others (Hilgard 1860)."

On upper slopes, hilltops, and other more xeric sites of an upland setting, honey locust, crabapple, wild plum, and red haw were noted to associate with the black prairie soil. In another instance, "large Sweet Gum, Ash, Elm, Cottonwood, Maple, and Water Oak" occupied tracts of "a few hundred acres, of jet black prairie soil, 2 to 3 feet deep" in creek bottoms.

The calcareous, black prairie soils were separated into those of "black" and "bald" character (Hilgard, 1860). The Bald Prairie was the upland prairie, sometimes designated as "Shell Prairie" from the great abundance of oysters and other fossil shells. The "excess of lime" soil profiles created the bald prairies that were often situated on hilltops. South of Quitman, in Clark County, of the "prairies which form plateaux or level ridges between the water courses," only a small portion is "really bare of timber."

Another prairie type, the "Hog-wallow Prairie," also termed "Post Oak Prairie," consisted of wooded areas, with soils black in color and noncalcareous, at least in the upper horizons (Hilgard, 1860). The name refers to the gilgai microtopography of the soil surface, composed of microbasins and microknolls. The heavy montmorillonitic clays of the "Hog-wallow Prairie" shrink and swell considerably with wetting and drying causing the uneven microtopography (Pettry and Switzer, 1993).

Hilgard recognized an additional prairie type, naming it "Gypseous Prairie," which referred to depressional areas of light, brownish-buff, productive "prairie" soil "because it bore no timber." The Gypseous Prairie soils were not calcareous and did not support species normally associated with the tall grass prairie or barrens described for other eastern states. Persimmon, winged sumac, and numerous leguminous plants were noted to be present on the Gypseous Prairies.

Brown (1894) provided additional anecdotes about the presence of prairies in the southwestern part of Newton County:

"Much open land and wide-spreading open prairies...covered with a growth of very rich grass and a very parterre of flowers...offered [the American Indians a] large scope for recreation and engagement in their national ball play. These bald places were occasionally relieved by a clump of trees, forming an oasis as in a desert. [They] were called the "shell lands," and in may instances, had a large accumulation of small shells in the soil, and a great number of oyster shells of large size. The oyster shells were largely used in early settlement of the county in making lime. These shell lands were only productive of corn and other grain. They would not make cotton--it would "rust." The shell prairies, heretofore bare of timber, are now producing haw, crabapple, and some other growths, which cause them to be harder to clear...The woodland prairie made fine cotton and corn. When the growth was post oak it produced cotton better. These lands required good plows to break and to bed up the ground...[In regards to grazing value] This upland grass was good, but nothing like that on the prairies. The prairie grass was a mixture of grass and herbs indigenous to the soil, and different from the upland grass, of which cattle were very fond and which was a great milk and fat producer. Most of these grasses have become extinct, or so dwarfed by constant grazing and tramping by stock, as not to be observed as an original grass."

Lowe (1911, 1913, 1915) described the region in a similar fashion, characterizing the soils as distinctly calcareous, forming limited areas of gently rolling "black or shell" prairies, not as large as those in the northeastern counties of Mississippi. Rostlund (1957) presented historic accounts by travelers and explorers, who described areas of the Black Belt Prairie that currently exist as small prairie openings. These accounts dated back to Hernando De Soto's expedition in the 16th century.

Materials and Methods

Study Sites

Four prairie remnants in the Jackson Prairie Belt were selected to characterize their soils (See Figure 1 ). The selected sites were Durand Oak Prairie and Harrell Prairie Hill in Scott County, Five-Acre Prairie in Smith County, and Eureka Church Prairie in Newton County (Table 1). Selection of the study sites was based on the size of the remnant, degree of disturbance, and proximity to other prairie sites.

The Jackson Prairie Belt is a gently-rolling upland region approximately 9 to 31 miles wide that is underlain by the Yazoo Clay of the Jackson Group. The topography is predominantly level, and mean elevation ranges from 196 to 295 feet (Pettry, 1977). The climate is temperate and continental with mild winters and hot summers (Murphree, 1957). Mean annual temperature (1960 to 1990) is around 18 °C, and mean annual precipitation about 58 inches (U.S. Dept. of Commerce, 1992).

The Yazoo Clay is a green to gray calcareous clay of Eocene Age. It is high in montmorillonite clay and reflects near-shore marine deposition (Merrill et al., 1985). The soils developed in the Yazoo Clay are fine textured with a dark gray, clayey surface horizon and a lighter gray subsoil (Dixon and Nash, 1968; Lowe, 1911). Montmorillonite constitutes more than 50% of the noncarbonate clays, resulting in high shrink-swell potentials and cation exchange capacities (Dixon and Nash, 1968). Kaolinite, illite, and vermiculite comprise the remaining portions (Ramathirtha, 1971).

Soil orders include Inceptisols, Vertisols, Alfisols, and Mollisols (Pettry and Switzer, 1993). DeSelm and Murdock (1993) commented that Alfisols with a clayey B horizon were diagnostic of the Jackson Prairie Region.

Laboratory Analysis

Representative pedons were described and sampled in excavation pits using standard methods (Soil Survey Staff, 1995). Undisturbed core samples were taken for determination of saturated hydraulic conductivity (K_s), bulk density (Bd), and moisture retention properties. Soils were classified according to the current national criteria (Soil Survey Staff, 1996). The soil samples were air-dried and sieved to collect the fine-earth fraction (<2 mm).

Particle size analysis was determined by the hydrometer method (Day, 1965). Saturated hydraulic conductivity was determined by the constant head method (Klute, 1965). Moisture retention properties were determined using pressure membrane techniques (Richards, 1949). Bulk density was determined using the core technique (Blake, 1965). Penetration resistance was measured with a Proctor Penetrometer.

Extractable bases were determined by NH₄OAC (ammonium acetate) extraction and atomic absorption spectrophotometry (Chapman, 1965a). Extractable hydrogen was determined by the barium chloride-triethanolamine method (Chapman, 1965b). Cation exchange capacity (CEC) was determined by the summation method. Organic matter was determined by acid dichromate digestion (Peech et al., 1947). CaCO₃ (calcium carbonate) Equivalency (CCE) was determined by the titrimetric HCl (hydrochloric acid) treatment (Richards, 1954). Soil pH was measured in 1:1 soil: water suspension.

Results and Discussion

Morphology

The soils were classified as very fine and fine, smectitic, thermic Chromic Hapluderts (Table 1). The major pedogenic processes in these prairie soils are melanization, argillipedoturbation, and calcification. Typical soil properties of Vertisols are: clay texture; strong granular structure in the upper 6 to 20 inches; calcareous to neutral reaction; gilgai relief; high shrink-swell potentials; plastic consistency; calcium (Ca) and/or magnesium (Mg) as the dominant cations; montmorillonite as the major clay mineral; calcareous parent material; thick sola; low chromas; high organic matter contents; little weathering; and tallgrass or savanna vegetation (Buol et al., 1989). The soils of this study met the requirements for Vertisol classification.

The morphology of the prairie pedons is presented in Tables 2 and 3. The epipedons at Durand Oak Prairie, Harrell Prairie Hill, and Five-Acre Prairie were classified as ochric epipedons because they were lighter in color and thinner than mollic epipedons. The soil surface horizons were commonly thicker and darker in the adjacent forests than the prairies (Moran, 1995).

The ochric epipedon at Durand Oak Prairie was 14 inches thick and included the Ap, A2, and AB horizons. The epipedon at Harrell Prairie Hill was 8 inches thick and included the Ap and BA horizons. These epipedons were too light in color for mollic classification, suggesting that the former mollic epipedons in the prairies have been severely truncated by accelerated erosion resulting in the formation of light colored ochric epipedons (Moran, 1995).

The epipedon at Five-Acre Prairie was 12 inches thick and included the Ap and BA horizons. The BA horizon was too light in color, and the Ap was too thin for mollic classification reflecting the impact of accelerated erosion.

The epipedon at Eureka Church was thick (13 inches) and dark (value of 3) and met the criteria for mollic classification. The mollic epipedon included the Ap and AB horizons reflecting the high degree of melanization. The Eureka Church site was level and exhibited little evidence of accelerated erosion.

The epipedons in the prairies had weak to moderate, fine, granular or angular blocky structures; friable consistency; and strong to violent effervescence, reflecting the extensive root system and high CaCO₃ contents. All the pedons had thick sola with firm, sticky, plastic cambic (Bw) horizons, with few to many intersecting tongue-and-groove slickensides, compound structures, and secondary carbonates.

Slickensides and pressure faces are common morphological features in expansive soils in Mississippi (Pettry and Switzer, 1993) and reflect the swelling pressures caused by argillipedoturbation (Lynn and Williams, 1992), the very high shrink-swell potentials, and the alternating wet and dry seasons in the Jackson Prairie Region. Compound structures extended to the surface at Five-Acre Prairie, but occurred only below 12-inch depths in the other prairie pedons. The coarse prismatic structures result from the increased overburden pressures from the surface and more uniform moisture contents that decrease the shrinking-swelling activity at the deeper depths. Fine roots along the prism faces and flat roots at the sides of the slickensides were common in pedons.

Soil hues ranged from 10YR to 2.5Y in the upper sola to 5Y or 2.5Y in the lower depths. Values ranged from 3 to 6 in the epipedons and from 6 to 7 in the subsoil. These colors reflect the inherent color of the Yazoo Clay.

A thick gypsiferous horizon (Bwssy) with medium and large crystals was present in the subsoil at Durand Oak Prairie and Harrell Prairie Hill. The presence of the gypsum crystals and the strong effervescence suggests these soils are supersaturated with respect to Ca⁺². The secondary gypsum crystals may form from sulfate ions released during the weathering of pyrite in the Yazoo Clay. A thick cemented calcareous horizon (Bkm) containing fossil shell fragments occurred at the 12-inch depth in Five-Acre Prairie. A dense Cr horizon was present below 46 inches at Eureka Church Prairie. Also, many fine, round, iron (Fe) and manganese (Mn) concretions occurred in the Bwk and Bwkss horizons at Eureka Church Prairie. The concretions may have developed from alternating reducing-oxidizing conditions caused by fluctuating water saturation due to the dense underlying Cr horizon. The low chroma colors in the pedon are inherited from the parent material. Few round quartz fragments in this pedon suggest a higher energy depositional environment or reworking of sediments.

Physical Properties

Selected physical properties of the prairie pedons are presented in Table 4. Clay textures were dominant in all depths at Durand Oak Prairie and Harrell Prairie Hill and in the lower sola at Five-Acre Prairie and Eureka Church Prairie. Maximum clay content was 84.9% in the C horizon at Durand Oak Prairie, and minimum clay content was 20.1% in the Bkm horizon at Five-Acre Prairie. Clay contents were lower in the epipedons and increased with depth, suggesting a different depositional environment or greater pedogenesis in the surface. Silt contents were commonly higher in the upper sola and reflect the precipitation of secondary carbonates.

Bulk density was lowest in the epipedons and increased with depth. The higher bulk densities in the subsoil result from the lower organic matter contents, less aggregation (compound structures) and root penetration, and the overburden pressures from the weight of the overlying horizons. The lower bulk densities in the epipedons reflect the high organic matter contents and root densities, and macrovoids. The higher bulk densities in the Bkm horizon at Five Acre Prairie and Cr horizon at Eureka Church Prairie reflect the strong cementation of the secondary carbonates.

Saturated hydraulic conductivity was higher (10-100 µm s^-1) in the upper sola and low (<0.1 µm s^-1) to moderate (0.1 to 10 µm s-1) at the remaining depths. High clay contents reduce the hydraulic conductivity in the lower sola. The high values in the epipedons reflect the aggregation, extensive root densities, and macrovoids in the surface. The low conductivity in the Bkm horizon at Five-Acre Prairie and the Cr horizon at Eureka Church Prairie suggest the plugging of pores during the secondary precipitation of the carbonates.

Penetration resistance was moderate (1 to 2 MPa) to high (2 to 4 MPa) and decreased slightly with depth. Resistance was typically influenced by the root density, the cementation of the free carbonates, soil moisture, and the particle size distribution. The higher resistance in the ochric epipedons at Durand Oak Prairie and Harrell Prairie Hill reflect the high root densities, whereas the higher resistance in the epipedons at Five-Acre Prairie and Eureka Church Prairie reflect the extensive root distribution and the secondary carbonate concretions.

Moisture contents at field capacity (0.03 MPa) and permanent wilting point (1.5 MPa) were moderate to high in all the horizons. The high moisture retention in the subsoil reflects the high clay contents. The high moisture contents in the epipedons are influenced by the clay and organic matter contents. The slightly lower moisture retention in the pedons at Five-Acre Prairie and Eureka Church Prairie is influenced by the many free CaCO₃ concretions and silt particles.

Chemical Properties

Selected chemical properties of the prairie pedons are shown in Table 5. The prairie soils have a high natural fertility with calcium as the dominant cation. Secondary carbonates contribute to the higher calcium contents in the soil. The gypsiferous horizons at Durand Oak Prairie and Harrell Prairie Hill had the highest extractable calcium contents.

The higher potassium contents in the lower sola reflect the mica content in the Yazoo Clay (Dixon and Nash, 1968). The higher extractable magnesium, potassium, and sodium in the lower sola also reflect the low degree of weathering in these soils. Extractable acidity is low in the sola and decreases with depth. The higher acidity contents in the epipedons indicate the dissociation of weak carboxylic groups and very weak organic acids in the organic matter (McBride, 1994). The lower acidity in the subsoil indicates acid weathering is not active.

Cation exchange capacities were high in all the pedons. The high CEC at the lower depths is influenced by the montmorillonitic clays, whereas the higher values in the epipedon are influenced by the high clay and organic matter contents. Base saturation was high (>90%) in all horizons and reflects the alkaline nature of the parent material. The base saturation in the lower horizons indicates the low degree of weathering in the prairie soils.

Soil pH was slightly (7.4 to 7.8) to moderately (7.9 to 8.4) alkaline throughout all the pedons. Typically, pH was slightly lower in the epipedon and increased with depth. McBride (1994) stated that increased CO₂ in the soil atmosphere caused by enhanced biological activity results in a decrease in pH and an increase in soluble Ca⁺² in carbonate-rich systems.

Soil organic matter was highest in the epipedons and decreased markedly with depth. The higher contents in the epipedons are indicative of the degree of melanization, enhanced by microbial decomposition, and intermixing of earthworms. Fine roots occurred to depths exceeding 40 inches and earthworms were present in the epipedons during pit excavation.

CaCO₃ content was moderate to very high and varied within the pedons. Free carbonates occurred as random masses uniformly distributed throughout the pedons at Durand Oak Prairie and Harrell Prairie Hill. Free carbonates in the pedons at Five-Acre Prairie and Eureka Church Prairie occurred as discrete, cemented horizons (Bkm and Cr horizons) or as small masses to large nodules. At Five-Acre Prairie, higher CaCO₃ contents in the Bkm horizon than in the underlying horizons suggest that Ca⁺² and CO₃^-2 ions were translocated in solution by capillary forces or leached through the A horizons and eventually precipitated to form the Bkm horizon and the carbonate masses and nodules in the adjacent horizons.

Carbonate in the pedon at Eureka Church Prairie varied from low to very high. Values were consistent with the soil reaction to 10% HCl registered in the field. The very high contents in the Cr horizon and the low contents in the overlying cambic horizons suggests carbonates were probably dissolved and leached in solution. The very high CaCO₃ contents in the Bkm horizon at Five-Acre Prairie and the Cr horizon at Eureka Church Prairie also reflect the presence of the unweathered fossil shell fragments.

Conclusions

Soils of four native prairie remnants were characterized and classified in the Jackson Prairie Belt of Mississippi. The prairie soils are classified as fine and very fine, smectitic, thermic Chromic Hapluderts on level to gently sloping upland positions. Soil classification is indicative of the high shrink-swell potentials and high color values inherited from the Yazoo Clay.

These soils have high natural fertility with Ca as the dominant cation. They are thick, alkaline, and clayey with high water-holding capacities. Ochric rather than mollic epipedons are common in these prairies. The epipedons are too light in color and too thin for mollic classification, but are high in organic matter. Diagnostic subsurface features include the presence of firm, sticky, plastic cambic horizons with free secondary carbonate flecks or concretions, compound structures, and few to many intersecting slickensides. The cambic horizons are indicative of the low degree of weathering in these soils. The ochric epipedons in the prairie remnants are indicative of the critical impact of accelerated erosion induced by cultural disturbance. Mollic epipedons are encountered in prairie areas lacking accelerated erosion.

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Table 1. Soil Classification of the Prairie Remnant Pedons.
Remnant	Size A	Geomorphic Position	Slope (%)	Soil Classification
Harrell Prairie Hill	47.4	Upland	5-7	very-fine, smectitic, thermic Chromic Hapluderts
Durand Oak Prairie	10.1	Upland	5-7	very-fine, smectitic, thermic Chromic Hapluderts
Five-Acre Prairie	10.4	Upland	0-2	fine, smectitic, thermic Chromic Hapluderts
Eureka Church Prairie	1.0	Upland	0-2	fine, smectitic, termic Chromic Hapluderts

Table 2. Morphology of the Pedons at Durand Oak Prairie and Harrell Prairie Hill.
Horizon	Depth (in)	Moist Color		Structure¹	Consistence² (moist)	Roots³	Reaction to HCl
		Matrix	Mottles
Durand Oak Prairie
Ap	0-3	10YR 5/3	none	1f gr	fr	3f,m,c	strong
A2	3-8	10YR 6/4	none	2m abk	sf	2f,m	strong
AB	8-14	10YR 6/8	none	2m pr/2m abk	sf	1f	violent
		2.5Y 6/2
Bwss	14-26	5Y 7/2	10YR 6/8	2m pr/2m abk	sf	1f	strong
Bwssy	26-50	5Y 7/2	10YR 6/8	2m pr/2m abk	sf	1f	strong
C	50-70	5Y 7/2	10YR 6/8	ma	sf	1f	strong
Harrell Prairie Hill
Ap	0-4	2.5Y 4/2	none	1f abk	fr	3f,m,	strong
BA	4-8	10YR 6/8	2.5Y 4/2	2m pr/2m abk	sf	3f	strong
Bwk	8-12	10YR 6/8	none	2c pr/2m abk	f	3f	violent
Bwkss	12-36	5Y 6/3	10YR 6/8	2c pr/2m abk	f	1f	violent
Bwkssy	36-56	5Y 6/3	10YR 6/8	2c pr/2m abk	f	1f	strong
C	56-76	5Y 7/2	10YR 5/8	ma	f	-	strong

¹Structure: 1=weak, 2=moderate;f=fine, m=medium, c=coarse, gr=granular, abk=angular blocky, pr/=prismatic parting to, ma=massive
²Consistence: fr=friable, sf=slightly firm, f=firm
³Roots: 1=few, 2=common, 3=many, f=fine, m=medium, c=coarse

Table 3. Morphology of the Pedons at Five-Acre Prairie and Eureka Church Prairie.
Horizon	Depth (in)	Moist Color		Structure¹	Consistence² (moist)	Roots³	Reaction to HCl
		Matrix	Mottles
Five-Acre Prairie
Ap	0-6	10YR 3/2	none	1c pr/2f gr	fr	3f,m	strong
BA	6-12	10YR 6/4	10YR 3/2	2c pr/2m abk	f	1f	strong
Bkm	12-16	10YR 7/3	10YR 7/8	1c pr/2m abk	fr	1f	violent
Bwkss1	16-22	10YR 7/8	5YR 7/2	2c pr/2m abk	f	1f	strong
Bwkss2	22-45	5Y 7/3	10YR 6/8	2c pr/2m abk	f	1f	strong
Bwss	45-65	5Y 7/3	10YR 5/6	2c pr/2m abk	f	-	strong
			10YR 6/8
C	65-75	5Y 7/2	10YR 5/6	ma	f	-	strong
			10YR 6/8
Eureka Church Prairie
Ap	0-6	2.5Y 3/2	none	2f gr	vfr	3f,m	violent
AB	6-13	10YR 3/1	none	2m abk	sf	3f	slight
		10YR 6/6
Bwk	13-24	10YR 6/6	none	2m pr/2m abk	sf	1f	none
Bwkss	24-46	2.5Y 6/2	10YR 6/6	2m pr/2m abk	sf	1f	slight
Cr	46-76	2.5Y 7/2	10YR 7/8	ma	sf	-	violent
			10YR 5/6

¹Structure: 1=weak, 2=moderate;f=fine, m=medium, c=coarse, gr=granular, abk=angular blocky, pr/=prismatic parting to, ma=massive
²Consistence: fr=friable, sf=slightly firm, f=firm, np=nonplastic; p=plastic; ns=nonsticky, s=sticky
³Roots: 1=few, 2=common, 3=many, f=fine, m=medium, c=coarse

Table 4. Physical Properties for Selected Soil Horizons in the Prairie Pedons¹.
Horizon	Depth (in)	BD (g cm-3)	Ks (um s-1)	PR (MPa)	FC	PWP	Clay	Silt	Sand	Texture
					------------------------%-----------------------
Durand Oak Prairie
Ap	0-3	0.94	73.3	2.19	53.2	42.5	64.6	27.0	8.4	Clay
A2	3-8	1.19	103.8	1.69	50.4	41.4	71.6	25.1	3.3	Clay
AB	8-14	1.20	0.5	1.29	49.7	40.8	74.6	22.8	2.6	Clay
Bwss	14-26	1.20	3.0	0.88	51.6	42.5	79.7	18.3	2.0	Clay
Bwssy	26-50	1.17	0.1	0.66	53.6	44.3	79.2	10.1	10.7	Clay
Harrell Prairie Hill
Ap	0-4	0.99	66.9	1.69	51.4	40.4	57.3	30.9	11.8	Clay
BA	4-8	1.09	81.9	1.60	48.4	41.9	68.2	27.4	4.4	Clay
Bwk	8-12	1.21	11.7	1.52	45.8	39.8	72.2	24.2	3.6	Clay
Bwkss	12-36	1.30	8.4	1.45	48.0	41.0	78.5	19.3	2.2	Clay
Five-Acre Prairie
Ap	0-6	1.04	41.5	1.40	40.2	32.3	31.6	35.6	32.8	Clay Loam
BA	6-12	1.35	18.9	3.49	34.5	29.4	40.2	50.0	9.8	Silty Clay
Bkm	12-16	1.46	0.6	3.67	26.1	19.0	20.1	74.4	5.5	Silt Loam
Bwkss1	16-22	1.39	22.8	1.60	40.4	34.4	64.5	29.7	5.8	Clay
Bwkss2	22-45	1.33	0.1	1.05	42.7	36.0	70.5	25.9	3.6	Clay
Eureka Church Prairie
Ap	0-6	1.19	31.8	1.75	33.3	27.5	27.5	44.9	27.6	Clay Loam
AB	6-13	1.32	30.9	2.65	33.6	28.3	45.0	40.5	14.5	Silty Clay
Bwk	13-24	1.34	38.6	1.55	38.3	33.1	53.4	37.8	8.8	Clay
Bwkss	24-46	1.40	3.0	1.24	33.3	28.7	57.8	33.2	9.0	Clay
Cr	46-76	1.31	0.1	ND	30.5	24.6	31.6	46.8	21.6	Clay Loam

¹BD=Bulk Density; Ks=Saturated Hydraulic Conductivity; PR=Penetration Resistance; FC=Moisture at Field Capacity; PWP=Moisture at Permanent Wilting Point; ND=Not Determined

Table 5. Selected Chemical Properties of the Prairie Pedons¹.
Horizon	Depth (in)	Ca	Mg	K	Na	H+Al	CEC	pH	BS	OM	CCE
		--------------cmolckg-1--------------							----------%----------
Durand Oak Prairie
Ap	0-3	53.1	2.2	0.8	0.1	4.8	61.0	7.5	92.1	5.5	19.4
A2	3-8	51.8	2.1	0.6	0.1	4.7	59.3	7.7	92.1	1.9	23.8
AB	8-14	50.8	2.4	0.6	0.1	0.3	54.2	7.8	99.4	1.1	24.2
Bwss	14-26	52.2	3.2	0.7	0.2	0.0	56.3	7.7	100.0	0.5	20.7
Bwssy	26-50	89.6	8.7	0.8	0.7	0.1	99.8	7.6	100.0	0.2	16.2
C	50-70	66.7	18.0	1.0	1.4	0.1	87.1	7.7	100.0	0.1	17.5
Harrell Prairie Hill
Ap	0-4	54.4	2.5	0.9	0.1	2.2	60.1	7.5	96.4	4.3	13.9
BA	4-8	48.9	2.5	0.5	0.1	5.1	57.1	7.6	91.0	2.0	19.9
Bwk	8-12	46.6