The most comprehensive review of Egyptian soils is provided in the FAO map of the world (FAO/UNESCO 1977). It is based on detailed soil maps (Elgabaly 1969; Veenenbos 193), and work by Ghaith (1959). It provides a comprehensive review of the distribution of Egyptian soils up to the mid- 1970s. The soil terminology used in this chapter is based on the FAO System of Soil Classification, excellent summaries of which appear in (FAO/UNESCO 1974) and Young (1976).
In the late 1980s the legend for the FAO/UNESCO Soil map of the world was revised (FAO/UNESCO 1988). This revised legend affects many of the soils in Egypt.
Mappable soils, those with even the slightest degree of horizonation, cover 79 599 km2 , or 83.15 percent of Egypt (FAO/UNESCO 1977).
The main Egyptian soil associations, in order of decreasing area, are: calcisols and gypsisols; mixed leptosols and regosols; calcaric fluvisols; solonchaks; regosols; lithic leptosols and mixed lithic leptosols; and calcisols and gypsisols (Table below). In addition there are minor occurrences of gleysols, vertisols, and solonetz soils within the major associations.
This table and the accompanying Map (Fig.below)
were based originally on the major soil types in the FAO Soil map of the world (FAO/UNESCO
1977). Since then the legend for the FAO Soil map of the world has changed but a new
map covering Egypt has not yet been produced. The overall calculations are therefore
based on the original map and legend, although new soil types have been used whenever
Calcisols and gypsisols
Large areas of calcisols and gypsisols are found in Egypt, especially in the Western Desert, on the Libyan Plateau, in the north-western and south-western parts of the Eastern Desert, long the southern Red Sea coast, and in Central Sinai (Fig. 2).
Calcisols are dominated by a calcium carbonate-rich horizon within 1.25 m of the soil surface. Their subsoil properties are variable, ranging from those with subsoil clay accumulation to those with no B-horizon development at all. The organic matter contents vary but they are never saline and neither do they exhibit evidence of gleying in the upper meter.
Gypsisols are similar to calcisols in terms of most diagnostic properties with the very important exception of the type of calcium accumulation in the upper 1.25m . In gypsisols this zone is dominated by gypsum (calcium sulphate). The lack of clay in many calcisols and gypsisols combined with the low amounts of organic matter means that most of these soils are characterized by inherently low fertility and poor water- holding capacity. Nevertheless, with irrigation and manuring or fertilizer application, they are being reclaimed on the desert land adjacent to the Nile Delta and in some of the Western Desert oases. The high calcium carbonate and calcium sulphate content of some calcisols and gypsisols can create further soil management problems. In many calcisols and gypsisols the calcium carbonate and sulphatr has aggregated and hardened to from calcrete or gypcrete, respectively. These are rock-like materials which create severe problems for root penetration and ploughing, especially as they are usually found in the upper 1.25m of the soil. A further physical problem, which is particularly prevalent when these soils have a high silt content and are irrigated, is surface crusting which dramatically reduces the infiltration rate. Other management problems are concerned with soil chemistry. The levels of available phosphorus are low due to the high pH, and the micronutrients such as copper, iron , manganese, and zinc also have low availabilities. There are often potassium and magnesium supply problems due to the calcium imbalance, and the soils have very low levels of microorganisms.
Lithic leptosols have severe depth limitations. Continuous outcrops of consolidated rock can be found within 10 cm of the surface and consequently there is minimal profile development.
Lithic leptosols are restricted mainly to mountainous south-west Egypt. They are found in combination with calcisols and gypsisols in the most mountainous parts of the Eastern Desert and Red Sea Mountains, in a belt extending from the Sudanese border north to about 29 oN, and on the southern tip of the Sinai Peninsula. Other isolated areas are found in the southern parts of the Western Desert, and a smaller area of lithic leptosols and regosols is restricted to the Egyptian - Israeli border in eastern Sinai (Fig. 2).
Cultivation is impossible on these soils due to their shallowness, limited nutrient supply, and very low water-holding capacity. Only localized land-use options, such as rough wet- season grazing, indigenous forestry, gathering plant products and hunting, or water catchment are available.
Calcaric fluvisols are relatively young soils developed on recently deposited colluvial, fluviatile, lacustrine, or marine sediments in the Nile Valley and Delta, and on some of the coastal plains. In addition, four isolated but extensive areas of calcaric fluvisols are found in the Red Sea Mountains (fig. 2)
Fluvisols still show some sedimentary stratification. Organic matter content decreases irregularly with depth (although it remains above 0.35 percent in the upper 1.25m) and the soils have sulphide-rich material within 125cm of the surface. Generally fluvisols exhibit little horizonation, except for a weakly developed A-horizon and peaty horizons. Calcaric fluvisols, however, are strongly calcareous, having significant amounts of free calcium carbonate at depths of 20-50 cm and pH 7. These are the most intensively farmed soils in Egypt and have a high development potential due to the ease of irrigation low water erosion potential, and their ability to be double- cropped. They do not, however, have very high nutrient levels, so the maintenance of fertility by traditional manuring practices or by high rates of fertilizer application is of particular importance in crop production. There are also potential wind erosion problems in silt - rich areas if the topsoil is allowed to dry out. The major management task is to control water supply and conserve soil moisture.
The Nile fluvisols are extensively irrigated and the management of irrigation scheduling and drainage is time- consuming. In addition, in areas with a high clay content, poor irrigation practices often lead to subsoil compaction and pan formation, secondary salinization, and gleying.
Solonchaks are the saline soils formed on recent alluvial and lacustrine material, often in closed basins, such as those found in the desert oases, or in the coastal sabkhas. They are commonly found in many of the major oases and depressions in the Western Desert, particularly in the Bahariya, Farafra, and Siwa Oases, the El Faiyum and Qattara Depressions, and in Wadi el Natrun. There is also a wide belt of solonchaks along the upper Nile Delta extending eastwards to the Sabkhat al Bardawil on the northern Sinai coast (Fig. 2).
A number of types of solonchaks are found in Egypt, but the main diagnostic feature of all solonchaks is their high soluble salt content. Gleyic solonchaks exhibit hydromorphic properties, such as waterlogging and reducing conditions, within 0.5 m of the surface. Some solonchaks lack hydromorphic properties but have extensive crystalline salt crusts with blisters, pressure is described as having a takyric phase. Orthic solonchaks lak salt crusts with either takyric or hydromorphic features in the top 50 cm of the soil, but do have a weakly developed organic A-horizon.
Solonchaks are extremely difficult soils to manage due to their severe salinity problems. The high soluble salt content affects crop growth in two ways. First the osmotic balance of the soil solution is altered, making it extremely difficult for roots to extract nutrients from the soil . This results in stunted growth and depressed yields unless salt- tolerant crop varieties are grown . Second, at soluble salt contents in excess of about 2 percent, toxic effects become important . In particular, accumulations of chloride and boron are important, while sodium only really affects the ionic balance of the soil solution. Soil management is concerned with the amelioration of the high soluble salt contents in areas where there are no toxicity problems. Various strategies such as flushing out salts with irrigation water, the addition of less saline soil material, and the use of salt- tolerant crops are favourable measures for the less saline solonchaks, but where the salt contents are highest agriculture is impossible.
Regosols are developed on sandy substrates and, apart from a rudimentary A-horizon with less than 1 percent organic matter, show no horizonation. Two types of Regosols are found in Egypt - calcaric Regosols and eutric Regosols. The former have accumulations of calcareous material and the latter are not calcareous at depth of 20 - 50 cm, but have a base saturation in excess of 50 percent.
In Egypt, Regosols are important only locally in a small number of restricted areas. Pockets of calcaric Regosols are found in a narrow strip along the Mediterranean coast from Ras el Kanayis to the Damitta Branch of the Nile, to the east and west of the Nile Delta, on the western and southern shores of Sinai, in the Dakhla Oasis, and on the Sudanese border (Fig. 2).
Regosols have low available water capacities and low inherent fertility. Their management involves irrigation together with the addition of clay and manure. Irrigation alone provides only part of the answer, because without the addition of clay and organic material most of the water quickly enters the groundwater leaving little held in the rooting zone for plants. The clay and organic matter also provide nutrients and , in particular, provide sites to hold nutrients in the rooting zone.
Other surficial materials
The non-soil units identified in Egypt, rock debris, desert detritus, dunes, and shifting sands, are found mainly in the inner Western Desert and the northern Sinai Peninsula. In these areas the soil management problems preclude any agriculture, apart from some desert nomadism.
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