Document Type : Original Article
Author
Pedology Department, Water Resources and Desert Soils Division, Desert Research Center ‎‎(DRC), Cairo, 11753, Egypt dr.elwan@drc.gov.eg
Abstract
Soil characteristics and processes are governed by soil formation factors. This study aimed to assess the influence of geomorphological units and related criteria of soil parent material and topographic feature on soil properties and formation in Wadi El-Ashara, Egypt. The impact of bedrock catenas and slope position as geomorphic criteria on soil properties was investigated in Wadi El-Ashara, West of Suez Canal. The obtained results were utilized to investigate variations in the existing diagnostic criteria of the World Reference Base (WRB) and USDA Soil Taxonomy schemes. To reach these objectives, ten soil pedons were characterized across two distinct catenas in Wadi El-Ashara. The study's findings revealed that soil salinity increased downslope on piedmont and basin floor landforms. The summit positions of two catenas have weakly developed soils, but the midslope and downslope positions have more developed soils because the stable topography permits the formation of gypsic, calcic, sodic, and salic horizons. By the USDA system, soils of limestone catena were classified as Lithic Torripsamments and Lithic Torriorthents at the upslope positions, Sodic Haplocalcids at the midslope position, and Typic Torriorthents and Typic Haplocalcids at downslope position. The soils at the toeslope of the limestone catena were grouped as Solonchaks by the WRB system, since the salinity fits the requirements of salic horizon in the WRB system, but did not fit according to the USDA system, which should be standardized. This feature strongly influences soil classification and soil types across the studied two catenas. Furthermore, the soils of uppermost areas of gypsum catena (summit and shoulder) were classified as Lithic Torriorthents and Leptic Haplogypsids according to USDA system instead of Leptosols and Gypsisols by the WRB system while soils in the backslope and footslope, with secondary gypsum accumulations, were categorized as Typic Haplogypsids by USDA system and Gypsisols by WRB system. Topography across slope positions induced differences in soil depth, soil texture, water retention, soil salinity, horizonation, and morphology of studied soils from the summit to the toeslope along both catenas. According to the study's conclusions, the current versions of the WRB and USDA systems have shortcomings that necessitate standardization in order to improve these systems and develop a uniform classification method. Parent material and topography across distinct slope positions were identified as the two primary soil-forming factors influencing soil properties in the two examined catenas at Wadi El-Ashara.
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