Variation in soil chemical properties along toposequences in an arid region of the Levant

doi:10.1016/j.catena.2010.07.002

CATENA

Volume 83, Issue 1, 15 October 2010, Pages 34-45

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Abstract

Detailed characterization of soils and their variation along different topography positions has not been investigated in depth for Mediterranean arid regions. There is a need to accurately understand the variation and the spatial distribution of soil properties within dry region of the Levant. Such understanding is required to optimize the use and management of scarce land and water resources. The objective of this study was to examine the effect of hillslope characteristics on the variation of selected soil chemical properties in an arid Mediterranean climate. At each of five selected transects four sites were chosen to represent four different topographic positions: summit, shoulder, backslope and toeslope. A soil profile was examined at each site and a representative sample from each horizon was withdrawn for chemical analyses. The analyses indicated that generally, the carbonate contents of the surface horizons decreased from higher to lower positions of the toposequence, the carbonate content increased with depth for profiles occupying the lower positions. This suggests more intense leaching within soil at lower positions. The effect of steepness and curvature on controlling the variation of soil properties was obvious at the summit and shoulder positions. Leaching process seems to hinder the effect of steepness and curvature for soils at lower positions. Lower positions receive runoff water and organic matter from upper positions, which complicate the relationship between landform shape and organic matter content. Continuous tillage resulted in lower organic matter contents for soils at lower positions. Higher pH values were reported for soils down along the transect due to the movement of soil material from upper hillslope positions. Electrical conductivity, exchangeable calcium and potassium contents decreased downslope due to higher moisture accumulation. However, no obvious relationship was found between the variation of pH or EC in one hand and the variation of steepness and curvature on the other. Potassium content was variable due to its greater mobility. The analyses indicated that variation in the soil CEC is governed by two factors: the leaching pattern, which is controlled by hillslope position, and the accumulation of Eolian carbonates at the soil surface. The distribution of iron oxides and types of clay minerals indicated more weathering in a descending direction and with soil depth, which is attributed to higher availability of soil moisture along the same direction. These relationships suggested systematic variation of chemical properties along toposequences in this arid environment.

Introduction

Understanding the soil chemical composition and its variation is essential for utilizing and managing the soils. Such information is usually collected as a part of soil survey activities. Users of such information are progressively requiring more details about the distribution of soil properties, for which small-scale soil survey is not sufficient, particularly for site specific applications (Young & Hammer, 2000, Pachepsky et al., 2001). Soil survey employs relationships between topographic features and the distribution of different soils. However, a quantitative relationship between soil topography and its chemical constituents is not well established for a wide range of environments. This is due to the complex nature of such relationship owing to the sensitive impact of topography on the movement of soil material, which makes this relationship site specific. The question about the magnitude and pattern of variations in soil properties within specific landforms is still unanswered (Young and Hammer, 2000). Many researchers linked the pedogenic processes, which control soil properties, to the variation of geomorphic features and considered that soils could be differentiated by their location within the toposequence (Huggett, 1975, Ovales & Collins, 1986). Other researchers took this relationship further by attempting to quantify the relationships between topographical parameters and soil properties. They found that variations of some soil chemical and mineralogical properties can be related to the slope steepness, length, curvature and the relative location within a toposequence (Aandahl, 1948, Acton, 1965, Ruhe & Walker, 1968, McKenzie & Austin, 1993, Moore et al., 1993, Gessler et al., 1995, Gessler et al., 2000). However, various relationships were found depending on the topographic positions and other factors affecting soil genesis but with a trend confirming that the movement of material within specific toposequence will control soil properties. Therefore, a hillslope sequence could be used to understand the variations of soil chemical properties in order to establish relationship between specific topographic positions and soil properties.

Toposequence is defined as “a spatial object that maintains flow connectivity from summit (hillslope initiation) to base (hillslope conclusion)” (Gessler et al., 1996). Because soils are an integral part of the land surface, any variations in the geomorphic and hydrologic processes influence the pedogenic processes through the effect on differential distribution of water, sediments and dissolve materials (Ovales & Collins, 1986, Young & Hammer, 2000, Brunner et al., 2004). Soils properties on a toposequence differ due to degree of erosion, transport and deposition of chemical and particulate constituents of the soil (Krasilnikov et al., 2005). The concept of toposequence, which involves processes that cause properties' differentiation along hillslopes and among soil horizons, was utilized to study the effect of tillage erosion and water erosion on the variation of chemical properties within different landscapes (Ni and Zhang, 2007). The topographic position of soil was among factors used to establish local soil classification that guides land use and management decisions (Gobin et al., 2000).

Many attempts have been made to quantify the relationships between topographical parameters and soil properties (Aandahl, 1948, Acton, 1965, McKenzie & Austin, 1993, Moore et al., 1993, Gessler et al., 1995, Ziadat, 2005). The variation of soil properties bears a sensitive relationship with the angle of gradient and to the length of slope. This is due to erosion and deposition processes operating along the slope, water percolation and runoff (Ni and Zhang, 2007). The distribution of surface soil properties over inclined topography is related to gradient and to the position of the soil with respect to distance down slope (Aandahl, 1948, Acton, 1965, Moore et al., 1993, Gessler et al., 1996). Researchers suggested some promising indicators such as pH, organic matter, exchangeable cations, total exchangeable basis, ratio of primary to secondary minerals, free oxides, carbonates and physical properties such as, particle size distribution, moisture content, color, bulk density and depth to specific horizon boundaries (McKenzie & Austin, 1993, Gessler et al., 2000, Pachepsky et al., 2001). Many soil chemical properties demonstrated good correlation with the slope steepness. Properties such as pH were found to be positively correlated with gradient on the upper parts of slope in calcareous soils, while organic matter content was negatively correlated with the gradient (Ruhe and Walker, 1968). Organic carbon was correlated with slope gradient (Nizeyimana and Bicki, 1992) and to distance from the summit (Ruhe and Walker, 1968).

Carbonate content and pH were found to be significantly correlated along descending slope (Brubaker et al., 1993), while contents of reduced iron were highest in the upper slope positions but decreased with decreasing slope, and were lowest in soil occupying the low land. Brubaker et al. (1993) also found that the variation of cation exchange capacity was associated with the clay contents and organic carbon. Regarding the mineralogical properties, it has been reported that soils formed at the downslope positions showed higher weathering status than soils in upslope positions. Ratios of resistant to non-resistant mineral vary markedly with slope position. This proves that much of the variation of clay content is due to in-situ chemical weathering (Nizeyimana and Bicki, 1992).

The main driver behind this research was the need to explain the relationship between soil properties and topographic position in the Mediterranean climate. Soil development in this region is genetically complicated by three important soil forming factors. First, relief is the most important single factor that control the soil variability. Second, due to fragility of this environment and absence of good vegetation, erosion by water is very effective. The third factor is that the clear influence of the topography is complicated by the regional wind erosion, where calcareous silt is brought in the region from remote areas. Very little literature is published on soil variability and its relationship with topographic positions within such fragile environment. The objective of this study was to examine the effect of hillslope characteristics on the variation of selected soil chemical properties in an arid Mediterranean climate in Jordan.

Section snippets

Materials and methods

The study area represents the arid region of the Levant. The dominant geological formations through the study area consist of Eocene–Paleocene limestone with cherts and Eocene–Paleocene limestone with chert layers or marls (Fig. 1) (Bender, 1974). Rainfall season starts from late October to early November and ends in late March, with total annual average of 100–200 mm. Maximum rainfall events occur during January and February. Mean maximum and minimum air temperatures during January are 13 °C and

Results and discussion

Carbonates: the distribution of total soil carbonates at the summit and shoulder positions indicated an increasing trend with depth for deep soils (Fig. 3), which were found on less steep slopes with flatter curvature (Fig. 2). This is attributed to lower erosion activity, which ensures higher moisture availability needed for leaching of carbonate (Ziadat et al., 2010). The distribution of total carbonates in soils occupying the toeslope position indicated a slight decrease or uniform

Conclusions

The movement of water and sediments over the landscape surface and through the soil profile, which is controlled by hillslope position, steepness, and land shape are considered among the primary factors that could be used to explain the variations in some soil chemical properties. Furthermore, land surface characteristics such as steepness and curvature of upper topographic positions contribute substantially to the variations in soil properties of soils occurring at lower positions of the same

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Variation in soil chemical properties along toposequences in an arid region of the Levant

Abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Conclusions

Catena

Geoderma

Geoderma

Catena

Geoderma

Catena

Geoderma

Catena

Catena

The characterization of slope position and their influence on the total nitrogen content of a few virgin soils of western Iowa

Soil Sci. Soc. Am. Proc.

The relationship of patterns and gradient of slopes to soils

Can. J. Soil Sci.

Geology of Jordan

No-tillage and soil-profile carbon sequestration: an on-farm assessment

Soil Sci. Soc. Am. J.

Exchangeable cation analysis of saline and alkali soils

Soil Sci.

Soil properties associated with landscape position

Soil Sci. Soc. Am. J.

Soil carbon storage prediction in temperate hydromorphic soils using a morphologic index and digital elevation model

Soil Sci.

Measurement of pH with the class electrode as affected by soil moisture

Soil Sci.

Soil-landscape modeling and spatial prediction of soil attributes. Special issue: integrating GIS and environmental modeling

Int. J. GIS

Progress in Soil-Landscape Modeling and Spatial Prediction of Soil Attributes for Environmental Models

Modeling soil-landscape and ecosystem properties using terrain attributes

Soil Sci. Soc. Am. J.