Soil Classification and Genesis in Part of Khorasan Province

Saline and sodic soils occupy an important part of Iran including the vast area in Khorasan province. Also due to secondary salinization, some of the arable lands are becoming salt-affected. It is important to characterize and classify these soils for better management and uses. Preliminary interpretation of aerial photos and using topographic map, the area was divided into different physiographic units, that is, dominantly piedmont alluvial plains and flood plains. In these units, 30 soil profiles were dug and described, and soil samples from each genetic horizon were collected for physical and chemical characteristics using standard USDA methods. The aridic and thermic were recognized as moisture and temperature regimes, respectively. The gypsiferous and saliferous marls are the parent materials, being main factor for soil salinization. Topography, wind erosion and human activities also contributed to soil salinization. Micromorphological studies have revealed the presence of secondary gypsum and calcium carbonate in some pedons, forming gypsic and calcic horizons, respectively. The soils are classified according to the USDA soil taxonomy. Two soil orders (Aridisols, Entisols) and six suborders (calcids, salids, gypsids, cambids, fluvents and orthents) have been identified in the area, and a new subgroup of sodic torrifluvents is proposed.