Under the high and long-lasting aridity, all terrestrial soils are extremely dry. The water content of terrestrial soils is well below the unavailable water capacity. Due to the lack of vegetation, the soils are almost free of organic material and have no visible humus horizon. Most soils have weak reddish to slightly brownish B-horizon with different thicknesses. The soils are usually covered with a layer of aeolian sandAeolian sand and/or stones. The top soil of hamadas is completely covered with medium gravel to coarse stones, while on serirs they are covered with coarse sand to fine gravel. The stones and gravel are covered with desert varnishDesert varnish. Some stones on the soil surface are polished by wind and have a shiny surface, which is also called desert varnish or patinaPatina. Under the stones, we often find a patch of white powdered gypsum. The stones and the sand coverSand cover lie on a thin silty layerSilty layer of a few mm thicknesses. This layer shows fine cracks and contains different amounts of carbonateCarbonate, while the sand cover and the upper soil horizon can be free from carbonate. Under the silty layerSilty layer occur crack polygons filled with sand. In the center of the polygons, there is often a patch of gypsum. Some mega-cracks reach depths of more than three meters and have widths at the soil surface from a few centimeters to a few decimeters. In addition, almost all upper soils have a platy structure. In the case of loamy upper soils, the platy structure has often a spongy or foamy structure. The subsoils have a very high bulk density. The genesis of most field properties is described in this chapter and some phenomena that are difficult to explain are presented in the chapter. Outside oases, birs, and wadis, the average organic material content is 0.18% and the nitrogen content is 134 ppm. The nitrogen is present in inorganic form. Due to the high solubility of nitrates, the highest amount is found in the subsoil from terrestrial soils. Groundwater soils are almost free of inorganic nitrogen. The chemical analysis showed that terrestrial soils contain different amounts of soluble salts, gypsum, and carbonates. In general, the content of soluble salts increases with increasing clay content. In terrestrial locations, the soluble salts and gypsum are usually enriched in the subsoil, the carbonateCarbonate in the topsoil. The pH of salt-rich samples is usually between 7.0 and 8.5, while the pH values of samples with low-salt content and salt-free samples vary between 6.5 and 10.0. The clay fraction of soils from Mesozoic sediments and quaternary sediments in southwest Egypt consists mainly of kaolinite.

General Soil Properties

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发表日期：

2025年

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Fayez Alaily

摘要

Under the high and long-lasting aridity, all terrestrial soils are extremely dry. The water content of terrestrial soils is well below the unavailable water capacity. Due to the lack of vegetation, the soils are almost free of organic material and have no visible humus horizon. Most soils have weak reddish to slightly brownish B-horizon with different thicknesses. The soils are usually covered with a layer of aeolian sandAeolian sand and/or stones. The top soil of hamadas is completely covered with medium gravel to coarse stones, while on serirs they are covered with coarse sand to fine gravel. The stones and gravel are covered with desert varnishDesert varnish. Some stones on the soil surface are polished by wind and have a shiny surface, which is also called desert varnish or patinaPatina. Under the stones, we often find a patch of white powdered gypsum. The stones and the sand coverSand cover lie on a thin silty layerSilty layer of a few mm thicknesses. This layer shows fine cracks and contains different amounts of carbonateCarbonate, while the sand cover and the upper soil horizon can be free from carbonate. Under the silty layerSilty layer occur crack polygons filled with sand. In the center of the polygons, there is often a patch of gypsum. Some mega-cracks reach depths of more than three meters and have widths at the soil surface from a few centimeters to a few decimeters. In addition, almost all upper soils have a platy structure. In the case of loamy upper soils, the platy structure has often a spongy or foamy structure. The subsoils have a very high bulk density. The genesis of most field properties is described in this chapter and some phenomena that are difficult to explain are presented in the chapter. Outside oases, birs, and wadis, the average organic material content is 0.18% and the nitrogen content is 134 ppm. The nitrogen is present in inorganic form. Due to the high solubility of nitrates, the highest amount is found in the subsoil from terrestrial soils. Groundwater soils are almost free of inorganic nitrogen. The chemical analysis showed that terrestrial soils contain different amounts of soluble salts, gypsum, and carbonates. In general, the content of soluble salts increases with increasing clay content. In terrestrial locations, the soluble salts and gypsum are usually enriched in the subsoil, the carbonateCarbonate in the topsoil. The pH of salt-rich samples is usually between 7.0 and 8.5, while the pH values of samples with low-salt content and salt-free samples vary between 6.5 and 10.0. The clay fraction of soils from Mesozoic sediments and quaternary sediments in southwest Egypt consists mainly of kaolinite.