Instrumentos de recopilación de información

According to the above last-mentioned soil map, soils of the Greater Damascus Basin were classified using the comprehensive soil classification system of the United States Department of Agriculture (USDA Soil Survey Staff, 1975). An essential attribute of this system is the nomenclature employed to classify different soil groups. The names of the mapping units are combinations of syllables, most of which are derived from Latin or Greek. Each syllable of a soil name carries a conception of soil character or origin, thus the name directly indicates the general kind of soil being classified (USDA Soil Survey Staff, 1999; Brady and Weil, 1996). This soil classification system has six categories. Beginning with the broadest, these

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categories are the order, suborder, great group, subgroup, family, and series. Soils of the study area, however, are classified at the subgroup level.

Aridisol, Entisols, Inceptisols, and Vertisols are the principal soil-orders found within the boundary of the Greater Damascus Basin. The spatial distribution of these soil- orders is illustrated in Figure 7.1, and brief description of them is given below.

Figure 7.1 the spatial distribution of soils of the study area (at order level) digitized from the soil map of Syria at a scale of 1:500,000 (USAID, 1982).

7.3.1. Order Aridisol (desert soils)

According to several authors (e.g.,Edwards-Jones, 2001; Ilaiwi, 2001; Berger, 1982), Aridisols (from the Latin aridus, for “dry”, and solum, for “soil”) are soils that are developed in areas where the potential evapotranspiration significantly exceeds the amount of precipitation during most of the year, and very little or no water percolates through the soil. Owing to the limited amount of water available in the soil profile, the soil development processes are less intense than in the humid areas. Thus, these soils inherit a lot of their morphological features from the underlying bedrocks.

Aridisols occupy a relatively large area (2000 km2 or 39% of the total study area). They cover almost all of the central and eastern part of the basin where the annual precipitation drops below 250mm. In addition, Aridisols are characterized by an aridic (hot and dry) soil moisture regime, and they have light colour as there is not enough vegetation to add organic matter to the soil profile. Furthermore, they often accumulate calcium carbonate, gypsum, and other materials that are readily leached from soils in more humid environments (Edwards-Jones, 2001).

To reduce the heterogeneity in this order category, classification is done at the next lower categories (Suborder, Great Group, and Subgroup). A complete list of the soil taxonomic categories identified in the study basin is given in Table 7.1.

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Table 7.1 Taxonomic classification of soils of the study area taken from the soil map of Syria at a scale of 1:500,000 (USAID, 1982).

Order Suborder Great Group Subgroup

Aridisol Orthid Calciorthid Typic Lithic Xerollic Camborthid Typic Lithic Xerollic

Entisol Orthent Torriorthent

Typic Lithic Xerorthent Lithic

Inceptisol Ochrept Xerochrept

Typic Lithic Petrocalcic Vertic

Vertisol Xerert Chromoxerert Typic Entic

The suborder Orthidis the only Aridisols suborder found in the region. Its subdivisions (great groups) are Calciorthids and Camborthids. The spatial distribution of soils of the study area at the level of Suborder and Great Group is shown in Appendix 23.

 Great Group Calciorthids: these are Aridisols that have an ochric epipedon (surface

horizon with little organic matter) and a calcic horizon (a subsoil horizon with a secondary accumulation of carbonates, usually of Ca). These soils cover about 12% of the total study area. They are split into three subgroups based on the depth of the soil and the amount of organic matter in the epipedon (Berger, 1982):

 Subgroup Typic Calciorthidsare deep soils (deeper than 100 cm).

 Subgroup Lithic Calciorthids are similar to Typic but they have bedrock within

50cm of the surface.

 Subgroup Xerollic Calciorthidshave more moisture and more organic matter than

Typic Calciorthids. They are encountered in areas where the moisture regime is a transition between the xeric (moist in winter and dry in summer) and the aridic.

 Great Group Camborthids: these are Aridisols with an ochric epipedon and a cambic

horizon (a subsoil horizon with some alteration of the parent material and a weak indication of development). These soils occupy nearly 27% of the total study area. They are characterized by the absence of a horizon of carbonate accumulation, and they have relatively homogeneous texture from the surface downward. Three subgroups are distinguished in the area under investigation, separated according to drainage characteristics, depth and the amount of organic matter in the epipedon (Edwards-Jones, 2001;Berger, 1982):

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 Subgroup Lithic Camborthidsare similar to Typic but the bedrock is found within

50cm of the surface and they generally have more organic matter than the Typic Camborthids.

 Subgroup Xerollic Camborthidsare like Typic but they have more organic matter

and are moist for longer periods than Typic Subgroup.

7.3.2. Order Entisols (new soils)

Entisols (from the root ent, for “recent”, and solum, for “soil”) are soils that have little or no indication of development of pedogenic horizons (USDA Soil Survey Staff, 1999). Entisols in the study area are generally found as shallow soils in mountainous regions (especially in the Anti-Lebanon Mountain range) where the rate of erosion exceeds the rate of soil development, and they occupy an area of about 1500 km2 (31% of the total study area). Some of these soils have an ochric epipedon, especially when they are to some extent protected from erosion. According to several authors (e.g., Edwards-Jones, 2001; Berger, 1982), Entisols may have any moisture or temperature regime, vegetation, or parent material. They are generally characterized by the absence of distinct horizons and by their mineral nature.

The Suborder Orthent is the only Entisols suborder encountered in the study basin, whereas two Great Groups are recognized based on their moisture and temperature regimes: Torriorthents and Xerorthents.

 Great Group Torriorthents: these are the dry Entisols of arid regions (occupying about 16% of the study basin). They are mostly calcareous and have a torric (aridic) moisture regime. Some are very gravelly and have coarse texture. They are separated into two Subgroups:

 Subgroup Typic Torriorthentsare relatively deep and gravelly.

 Subgroup Lithic Torriorthentsare shallow to moderately deep soils.

 Great Group Xerorthents: these are soils of sub-humid climate that have a xeric moisture regime (Kolay, 2007). They cover about 15% of the total study area. They are mostly steep and lose water via runoff. Only one Subgroup is distinguished: namely Lithic Xerorthents.

 SubgroupLithic Xerorthentsare shallow to very shallow soils.

7.3.3. Order Inceptisols (young soils)

Inceptisols (from the Latin inceptum, for “beginning”, and solum, for “soil”) are soils of semiarid to sub-humid environments that generally show only moderate degrees of soil weathering and development (USDA Soil Survey Staff, 1999). Even though they are better developed than Entisols, they are still young soils and resemble very closely the parent material (Harpstead et al., 2001). They cover an area of about 1100 km2 (23% of the total study area).

The Suborder Ochreptis the only Inceptisols suborder recognized in the study basin. Its soils are found in the regions with xeric moisture regime, and accordingly, only great group is recognized, namely Xerochrept.

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 Great Group Xerochrepts: these soils are moist in winter and spring but are completely dry in summer (Edwards-Jones, 2001; Berger, 1982). Soils of this great group in the study basin are mostly deep and developed on Neogene deposits. They are usually characterized by an ochric epipedon and a cambic horizon. Four subgroups are recognized in the study area:

 Subgroup Typic Xerochrepts are deep to moderately deep, nearly level to undulating, well drained soils.

 Subgroup Lithic Xerochrepts are shallow and the bedrock is found within 50 cm of the surface.

 SubgroupPetrocalcic Xerochreptsare deep, well drained soils.

 Subgroup Vertic Xerochreptsare clayey soils that have deep, wide cracks in the summer if they are not irrigated.

7.3.4. Order Vertisols (cracking clay soils)

Vertisols (from the Latin verto, for “vertical cracking“, and solum, for “soil”) are soils with a high clay content that mainly developed under a xeric moisture regime (Al- Qudah, 2001). The most significant feature of these soils is the presence of deep and wide cracks which may extend to a depth of 1 m or more (Ahmad, 1996; Brady and Weil, 1996). These soil occupy an area of about 330 km2 (6% of the total study area) and have a fine texture. All Vertisols in the study basin belong to the Xerertsuborder in which only the Great Group Chromoxerert is recognized. Soils of this great group, however, are separated into two subgroups, namely Typic Chromoxerert and Entic Chromoxerert. The Typic subgroup is better drained and lighter colour than the Entic one (Berger, 1982).