Mineralogy of Saudi Arabian Soils: Central Alluvial Basins

These investigation were conducted to provide basic soil chemical, physical, and mineralogical data for an area of Saudi Arabia that had not been studied and for which greatly increased agricultural development is anticipated. Fourteen soils were collected from two arid interior basin areas of Saudi Arabia. The silt and clay mineralogy was studied using x-ray diffraction, differential thermal analysis, and electron microscopy. Quantitative estimation of clay-sized minerals was based on a combination of chemical and x-ray diffraction techniques. The calcareous soils of the central basins show minimal profile development. Particle size classes range from sandy-skeletal to fine silty. Soils with shallow water tables are saline with large SAR values. The clay minerals in soils of the basins are primarily inherited. Soils developed in alluvium from mixed igneous rocks have clay fractions in which smectite> mica> kaolinite> chlorite, palygorskite, vermiculite. Soils formed from Permian sedimentary rocks have kaolinitic clay fractions. It is postulated that the central basins do not receive sufficient Si inputs for palygorskite neoformation and it is thought that palygorskite is detrital, originating from eastern region Tertiary rocks. The soil clays of the central basins have greater smectite contents than those of the kaolinitic western highland soils and palygorskite-rich eastern-region soils