Soil Science Society of America Journal 66:1882-1888 (2002)
© 2002 Soil Science Society of America
DIVISION S-5—PEDOLOGY
Vertic Soils in Alluvion-Reclaimed Areas, Volturno River Plain, Italy
A. Ermice*,a,
M. Murolob,
M. L. Puglianoc and
C. Buondonnod
a Dipartimento di Scienze Ambientali, Seconda Università degli Studi di Napoli, Via Vivaldi, 81100 Caserta, Italy
b Dipartimento di Scienze Chimico-Agrarie, Università degli Studi di Napoli "Federico II", Via Università, 100, 80055 Portici, Napoli, Italy
c Dipartimento di Scienze Chimico-Agrarie, Università degli Studi di Napoli "Federico II", Via Università, 100, 80055 Portici, Napoli, Italy
d Dipartimento di Scienze Chimico-Agrarie, Università degli Studi di Napoli "Federico II", Via Università, 100, 80055 Portici, Napoli, Italy
* Corresponding author (Antonella.Ermice{at}unina2.it)
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ABSTRACT
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Reclamation activities in alluvial depressions in Volturno River Plain resulted in the occurrence of soils with vertic characteristics and properties. We studied the genesis and properties of soils in alluvial areas known to be reclaimed by the alluvion system about 100 yr ago, and compared these soils with natural, adjacent alluvial soils. Soils in the reclaimed areas were characterized by cracks, slickensides, and high clay contents. Soils were satisfactorily classified within the existing Vertisol order of U. S. soil taxonomy. Soils with similar vertic morphology and properties also occurred in nonreclaimed adjacent alluvial areas, where they were associated with coarser textured Entisols. Since no important morphological evidence for the reclamation activity was identified in the soils in the reclaimed areas, the anthropogenic origin of such soils only emerged from historical records. The introduction of relational properties such as historical records is currently suggested to interpret and classify soils of various proposed taxonomic classes at different categorical levels. Therefore we discuss some critical aspects of the use of the historical records for classifying the soils in the reclaimed areas into genetic and technical soil categories that are currently being defined by the International Committee on Anthropogenic Soils (ICOMANTH).
Abbreviations: CEC, cation-exchange capacity • ICOMANTH, International Committee on Anthropogenic Soils
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INTRODUCTION
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SOILS WITH VERTIC CHARACTERISTICS and properties, such as deep cracks when soils are dry, intersecting slickensides, and wedge-shaped structural aggregates in the subsoil, surface mulching and clay texture are widely reported in alluvial depressions (Ahmad, 1983, 1996; Allen and Fanning, 1983). In southern Italy, the need to acquire lands for agricultural use prompted the reclamation of alluvial depressions. The study of such reclaimed areas represents an opportunity to investigate a different aspect of the human impact on soils.
The effects of human activities on soil genesis, morphology, and properties, and the taxonomic collocation of the human-influenced soils have received increasing attention among soil scientists in recent years (Buondonno et al., 1998; Evans, 1997; Fanning and Fanning, 1989; Short et al., 1986; Strain and Evans, 1994). In particular, some case studies suggest that the inclusion of some human-disturbed soils into U.S. soil taxonomy may require a deviation from the current soil morphology criteria for using those of relational properties (Evans, 1997; Strain and Evans, 1994). The introduction of relational properties is one of the issues debated by ICOMANTH in the Circular Letters no. 1, 2, and 3 (ICOMANTH, 1995, 1997, 1998). Here, historical evidence is submitted as one of the tools for defining new classes in U.S. soil taxonomy (Soil Survey Staff, 1999).
We investigated the soils of an area known to be reclaimed by human-induced river overflows and subsequent sedimentation of earthy materials (known as the "alluvion" system), and compared them with adjacent alluvial native soils. The aims of this work were (i) to study the genesis, morphology, and selected properties of vertic soils in reclaimed areas; and (ii) to better appreciate some implications of the use of historical records on anthropogenic soil interpretation and classification in the U.S. soil taxonomy classification system.
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MATERIALS AND METHODS
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We conducted the study in Castel Volturno town and neighboring sites, in the western region of the Volturno River Plain, southern Italy (Fig. 1)
. This large plain is bordered to the north by the Roccamonfina volcano, to the east by carbonate mountains of the Campanian Apennines, to the south by the volcanoes of the Phlegrean Fields, and to the west by the Tyrrhenian Sea. Coastal dunes occur in the southwestern coastal strip of this plain. The Volturno River Plain was formed by Holocene alluvial sediments partially overlying pyroclastic materials and Plio-Pleistocene lacustrine, palustrine, or marine sediments. The sequence of the Plio-Pleistocene sediments indicated marked tectonic subsidence of the alluvial plain in question (Ortolani and Aprile, 1985; Romano et al., 1994).
The study area, which excluded the coastline and urbanized areas, comprises about 5600 ha, with an elevation ranging from 1 to 3 m above sea level. The area in question has a fluctuating water table at depths ranging from about 70 to 250 cm. It has a Mediterranean climate with an average annual temperature of 16.8°C, and an average annual rainfall of 991 mm. Rain is mainly concentrated from October to April, while less intense rainy events are from May to September. Most of the nonurbanized land area is used for livestock farming, generally with irrigated fodder crops. The most commonly grown crops are corn (Zea mays), alfalfa (Medicago sativa), barley (Hordeum vulgare), clover (Trifolium spp), ryegrass (Lolium spp), and oat (Avena sativa).
Because of major tectonic subsidence, the study area was characterized by the presence of marshlands until the beginning of the nineteenth century. Through historical research, conducted at the Public Records Office of Rome, Naples, and Caserta, at the land-reclamation consortium of the Lower Volturno, and at the National Library of Rome, we ascertained that most of the marshy areas were reclaimed from 1811 until the early 1900s. Such interventions, intentionally studied and realized as land-building practices, affected an area of about 3500 ha, and were achieved by the alluvion system. By this system part of the river waters were diverted and canalized, without the prevention of the natural river dynamics in the other parts of the alluvial plain. The system aimed at elevating the land surface by filling the marshy areas with alluvial sediments. River overflows were channeled to low-lying areas; that is, such areas were expressly delimited and essentially constituted sedimentation tanks. Here, floodwater remained until the sediment was deposited, and then the sediment-free water was removed. The system was based on a canal diversion network, with the water being drawn directly from the river bottom, and flowing into the sedimentation tanks. Such canals branched into other diversion canals reaching the inner parts of the sedimentation tanks. The induced overflows and the sediment deposition were adjusted depending on the river flood and on the prearranged increase of the surface level. From the examined documentation, the land surface in the study area was made about 120 cm higher.
Field and Laboratory Investigations
The reclaimed land was mapped by reconstructing the ancient plans realized in the area in question (Fig. 2)
. Grids approximately 200 ha wide were used to select 10 soils from both reclaimed and nonreclaimed areas. Six soils were sampled in the reclaimed areas, and two soils in the nonreclaimed areas (Fig. 2). The characteristics of the other two soils in the nonreclaimed areas on the Volturno River were reported elsewhere (Buondonno and Violante, 1985). Considering the duration of the reclamation activity in the locations of the sampled soils, we calculated that the ages of these soils are 123 yr for Soil 1, 115 yr for Soil 3, 105 yr for Soil 4, and 90 yr for Soils 2, 5, and 6.
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Fig. 2. Map of study area showing the locations of the selected soils. In the nonreclaimed areas the Locations 1 and 2 are those of Soil NR1 and Soil NR2, respectively.
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The soils were excavated to a depth of either 2 m or the top of the groundwater capillary fringe, whichever was shallower. In the field the following morphological features were described (Soil Survey Division Staff, 1995): horizon depth, color, texture, moisture, carbonate concentrations, structure, cracks, slickensides, consistence, and horizon boundaries. Bulk samples from horizons were collected. The samples were air-dried and sieved to obtain a homogeneous sample of <2-mm material for the following laboratory analyses: particle-size distribution, determined by sieve and pipette methods, after destruction of the organic matter with H2O2 and removal of carbonates with 1 M NaOAc (Gee and Bauder, 1986); organic C, according to the Walkley-Black oxidation method (Nelson and Sommers, 1996); CaCO3, determined by treatment with excess HCl and volumetric determination of CO2 (Loeppert and Suarez, 1996); cation-exchange capacity (CEC), determined by extraction with 1 M NH4OAc (pH 7) (Sumner and Miller, 1996); soil reaction (pH), determined in water suspension and in 1 M KCl (1:2.5 soil/solution). Soils were classified according to Soil Survey Staff (1999).
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RESULTS AND DISCUSSION
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Soils in Reclaimed Areas
Table 1 summarizes the morphological features of soils selected in reclaimed areas. Soils had homogeneous soil profiles without lithological discontinuities, except for Soil 1 which had a 2C horizon at a depth of 120 cm. The A horizons were generally thick and, in some cases, under agricultural use, were differentiated as Ap horizons. Surface horizon colors were mainly dark or very dark brown, or grayish brown, and the subsurface horizons were grayish brown or gray. Most of the subsurface horizons were mottled with redoximorphic features, indicating the occurrence of oxidation-reduction phenomena. Subsurface horizons also contained carbonate concentrations (10YR8/2 and 6/3) mainly in the form of masses. Rock fragment content was very low throughout, except in the Bssg horizon of Soil 6, which contained some brick fragments.
During the dry season, the upper soil horizons were characterized by cracks 1 to 4 cm wide on the surface and 1 cm to a few millimeters wide at a depth of about 50 to 60 cm. The narrowest cracks occurred in Ap horizons, because of the effect of the plowing. Both Ap and A horizon surfaces had a layer 2 to 3 cm thick consisting of fine subangular blocky or granular aggregates. Cracks bounded prism units 3 to 30 cm across that parted to blocky structure in the upper 25 to 30 cm. Subsoil horizons exhibited strong or moderate angular and subangular blocky structure, except for the 2C horizon of Soil 1, which had no structure.
Below a depth of about 50 cm, all soils showed slickensides 3 to 40 cm across that increased with depth and were only lacking in the 2C horizon of the Soil 1. Except for the 2C horizon of Soil 1 which was loose, soil horizons were hard to rigid when dry, and firm to rigid when moist, and plastic and sticky when wet. The horizon boundaries were clear to diffuse and generally had smooth topography.
Chemical and physical properties of soils in reclaimed areas are reported in Table 2. All the horizons had a clay concentration from 36.5 to 78.6%, except for the 2C horizon of Soil 1, which had a loamy sand texture. In the most of the soils the highest clay concentrations were measured in the subsurface horizons. Clay-rich soil horizons generally had much more silt than sand concentrations. All soil horizons were slightly to strongly alkaline with pH (H2O) ranging from 7.4 to 8.7. Organic C, varying from 0.6 to 24.1 g kg-1, generally decreased regularly with depth. Calcium carbonate equivalent varied from 55 to 210 g kg-1, according to the variability in CaCO3 concentration of the alluvial materials used for the reclamation, which depended on the source lithology upstream. The clay-rich horizons had CEC values from 21.0 to 37.3 cmol (+) kg in spite of the low or moderately low organic C concentrations (2.0–24.1 g kg-1), suggesting the occurrence of some high CEC minerals in the clay fraction (Coulombe et al., 1996). The CEC to clay ratios probably indicated a mixed mineralogy in all soils.
The above data indicated that the soils in the studied reclaimed areas had marked vertic characteristics. As summer rain events prohibit cracks from remaining open for 
60 consecutive days and the wet period starting in October leaves cracks open for <150 cumulative days per year, we interpreted an ustic bordering on udic soil moisture regime for these soils. Therefore, two soils met the criteria for the classification of Udic Haplusterts: Soil 1: fine, mixed, superactive, thermic Udic Haplustert; Soil 3: very fine, mixed, semiactive, thermic Udic Haplustert. The remaining soils met the criteria for the classification of Chromic Udic Haplustert: Soils 2, 4, and 6: very fine, mixed, active, thermic Chromic Udic Haplustert; and Soil 5: fine, mixed, active, thermic Chromic Udic Haplustert.
The soils in reclaimed areas mainly developed in alluvial materials used for reclamation by the alluvion system. In the studied soil locations, the reclamation was completed in the space of about 10 yr, and it stopped 123 to 90 yr ago. This indicates that the land surface in the reclaimed areas had undergone a rapid rejuvenation. Therefore, the vertic properties characterizing the soils in these areas were rapidly developed compared to the pedogenesis reported for other soils with vertic properties (Mermut et al., 1996; Yaalon, 1971).
Soils in Nonreclaimed Areas
The morphological features and the selected chemical and physical properties of two soils in the nonreclaimed alluvial surface areas are reported in Tables 3 and 4, respectively. (See also soils in nonreclaimed areas described by Buondonno and Violante [1985]). Both soils had an Ap horizon because of agricultural use.
Soil NR1 showed evident vertic characteristics, such as frequent wide cracks, large and medium slickensides. The soil horizons had subangular to angular blocky structure, were hard to very hard when dry and very firm to extremely firm when moist, and had clear to diffuse horizon boundaries. Clay was >30%, pH was moderately alkaline (H2O). Organic C was moderately low and decreased regularly with depth. Carbonate ranged from 70 to 100 g kg-1 varying irregularly with depth, and CEC was high (36.7–31.0 cmol (+) kg) with slightly higher CEC to clay ratios than the reclaimed soils. The soil was classified as a fine, mixed, superactive, thermic Chromic Udic Haplustert.
Soil NR2 showed fluventic characteristics, such as stratifications with different particle-size distributions. Soil horizons had mainly subangular blocky structure or were structureless, had few narrow cracks, and lacked slickensides. Consistence was loose to moderately hard when dry, and from loose to friable when moist. Horizon boundaries were generally abrupt. The upper 60 cm had a loam texture, and the subsoil had sandy loam and sand textures. The pH was moderately alkaline (H2O). Except for the Ap horizon, the organic C was very low or low (2.0–7.8 g kg-1). The carbonate content was higher than that of Soil NR1 and varied irregularly from 140 to 230 g kg-1. The CEC varied from 7.3 to 23.4 cmol kg-1. This soil was classified as a coarse-loamy, mixed, thermic Oxyaquic Xerofluvent.
Historical Records in Classifying the Soils in the Reclaimed Areas
Historical records are not admitted in U.S. soil taxonomy as soil classification criteria. Although the current approach to soil classification is widely supported (Ahrens and Engel, 1999), the introduction of relational properties, such as historical records, has been suggested to recognize and classify anthropogenic soils (Strain and Evans, 1994; Evans, 1997; Bryant et al., 1999). Using such proposed criteria, the soils in the investigated reclaimed areas could be considered anthropogenic soils, as they can be proved to be derived from human activity via historical records. The definition and the appropriate collocation of such soils in U.S. soil taxonomy are currently being debated by ICOMANTH (1995, 1997, 1998). For their placement within the system, the introduction of either new genetic categories or technical classes is proposed.
The collocation of the soils studied in the reclaimed areas in new genetic categories presents some critical aspects. The soils in question had soil morphology and properties satisfactorily consistent with the existing categories of Vertisols (Soil Survey Staff, 1999). No major evidence of human intervention in the soils in question was identified. The soils in reclaimed areas did not differ from adjacent naturally formed soils that contain vertic characteristics. They also showed no variability in their gross soil morphology and characteristics, unlike other soils identified as human-influenced soils (Shafer, 1979; Buondonno et al., 1998; Hernandez and Galbraith, 1997).
Furthermore, the soils in question occurred in a floodplain and the human-caused parent material deposition mimicked the deposition of fine sediments in interfluve basins by natural flooding. This is in considerable contrast to, for example, the fluventic morphologies of soils occurring on Chinese anthropic terraces reported in the Circular Letter no. 1 of ICOMANTH (1995). Therefore, it would appear unwarranted to group the studied vertic soils in the studied reclaimed areas into genetic categories other than those of the current Vertisol category.
Finally, the use and management of the soils in the reclaimed areas did not differ from those of most of the soils in the studied alluvial plain. Therefore, the collocation of the studied vertic soils in appropriate technical categories would not be supported by any special considerations of soil use and management. Therefore, since new taxonomic treatment would result from the use of historical records to interpret human-affected soil genesis (i.e., Anthrosols vs. Vertisols), such use did not seem suitable for these vertic soils.
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SUMMARY AND CONCLUSIONS
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The pedological environment of the studied Castel Volturno alluvial plain consists of soils from alluvial materials deposited by either natural events or human activity. The natural soils were Vertisols or Entisols, according to the occurrence of clay-rich horizons with cracks and slickensides, or different particle-size stratifications, respectively. The human-influenced soils were derived from earthy materials used in reclamation by the alluvion process. Such activity highly modified large parts of the studied alluvial plain, transforming marshes to nonmarshy areas. The new soil thickness had vertic soil morphology and properties that are developed in a space of about 100 yr. By using historical records can we interpret the soils in the reclaimed areas as human-influenced soils. Nevertheless, no problems emerged with their classification as Vertisols, consistent with the current requirements of U.S. soil taxonomy. For the studied vertic soils, the use of historical records as a tool for soil classification could mean that soils which satisfactorily meet the criteria of existing soil categories might not be treated appropriately. On the other hand, historical records proved to be the essential tool for the recognition and interpretation of the studied human-influenced soils. Whether historical records should always be adopted as a criterion to classify human-influenced soils, or whether they could also be used only to acknowledge the changes induced by humans on soil and landscape, as suggested by this case study, is one of the open questions about human-influenced soils.
Received for publication January 2, 2001.
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ABSTRACT
INTRODUCTION
