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Soil is the natural medium for the growth of land plants, whether or not it has discernible soil horizons. People consider soil important because it supports plants that supply food, fibers, drugs, and other human needs and because it filters water and recycles wastes. All terrestrial life ultimately depends on soil, energy, and water. Soils have always been central to human civilization and life. They are an integral part of the physical and cultural environment, and we may take them for granted and even tend to treat them contemptuously.
The main features of desert soil that affect water and nutrient availability include texture, content of organic matter, pH, and orientation within the landscape. Desert soils show typically little development from parent material and some authors even state that typical developed soils do not exist in deserts. Most desert soils are classified as Aridisols and are differentiated into soils with a clay (argilic) horizon (Argids) and soils without such horizons (Orthids). Other soils, less common in deserts, are mollisols, soils with dark A horizons, and Vertisols, cracking clay soils. Accumulated subsurface horizons with either clays or calcium
carbonate (calcic horizons) have clear implication as impediments to water infiltration.
Most desert soils tend to be slightly to highly basic. Such reactivity can negatively affect phosphorous and micronutrient availability as these are generally not in solution at pH > 7.0. Organic matter helps to increase infiltration and via decomposition adds to nutrient availability. It is often distributed unevenly in desert soils (see below).
Soils in deserts have important effects on water inputs as they act as short-term water stores and modify water availability by a number of regulation processes. These regulation processes include direct infiltration and often more importantly runoff and horizontal redistribution of water. Redistribution by runoff tends to be of crucial importance in deserts and contributes to spatially very patchy distribution of water. Relatively impermeable surfaces (e.g., biotic or physical crust in clay-rich soils) create runoff areas that result in catchments that are water rich. Such water redistribution enables patchy plant production even in extreme arid zones, where plant growth would not be possible since evenly distributed sparse rainfalls would not exceed the threshold needed for plant life. Because of sparse plant growth, soil-created redistribution of water is more important than precipitation interception through plant surfaces. However, locally such interception combined with stem flow can create water-rich spots under shrub or tree canopies. In contrast, smaller precipitation events can be locally intercepted and lost by evaporation. This is the reason that soils in the understory of desert shrubs or trees can be either wetter or dryer than the surrounding soil.
Soil texture is of large importance as it affects both infiltration and the movement of wetting fronts. Fine-textured soils that are high in clay and silt fraction tend to impede infiltration, in which wetting fronts move only very slowly, and surface evaporation after rainfalls can be very high. More-coarse-textured soil rich in sand fractions, as for instance sandy loams, is characterized by high infiltration rates and rapid percolation. For this reason, coarse-textured soils are often better for plant growth. As this is in contrast to soils in mesic areas where fine- textured soils are commonly considered to be superior for plant production, this is called the ‘inverse texture effect’.
Clearly, the orientation and dynamics of soil surfaces within the landscape plays a large role in arid ecosystems.
SOILS IN UAE
The UAE is made up of seven emirates (States) and no one color of sand is specific to each emirate but multicolored sands are continuously shifting across and outside the UAE.
Soil Discovery in UAE
A soil rich in anhydrite (CaSO4) which had not been described before anywhere in the world as a soil class was discovered by Dr. Shabbir A. Shahid, a senior soil scientist at the Dubai-based International Center for Biosaline Agriculture (ICBA) and his co-associates Dr Mahmoud Abdelfattah and Khaliq ur Rahman Arshad at the Environment Agency – Abu Dhabi (EAD) discovered in the coastal lands of the UAE ( Al Dhabaya area of Abu Dhabi).
The soil scientists of ICBA and EAD in collaboration with scientists from USA submitted a proposal to USDA-NRCS to consider its addition to the US Soil Taxonomy. The proposal was accepted and the anhydrite soil added into the twelfth edition of US Keys to Soil Taxonomy published in 2014. The anhydrite soil was added at various levels.
A new sub-surface diagnostic horizon “Anhydritic” was added, with this addition globally the number of sub-surface diagnostic horizons increased to 20.
A new soil mineralogy class (Anhydritic) was added, with this addition globally the number of soil mineralogy classes increased to 33.
A new soil subgroup “Anhydritic Aquisalids” was added, with this addition the number of soil subgroups under the great group Aquisalids is increased to 4.
A new soil subgroup “Anhydritic Haplosalids” was added, with this addition the number of soil subgroups under the great group Haplosalids is increased to 6.
David W. Smith, Soil Science Division Director of the Natural Resources Conservation Service of the USA, in the Foreword of the 12th Edition of US Keys to Soil Taxonomy published in 2014 has highlighted that one of the changes in this edition is the recognition of the occurrence of anhydrite (CaSO4) in soils with the addition of a new diagnostic horizon, a new mineralogy class, and new Anhydritic subgroups for use in soil surveys. These are significant improvements to soil taxonomy which resulted from international collaboration with soil scientists of the UAE, where the soils with anhydrite were discovered.
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