Characterization and classification of desert depressions soils in Najaf province

Three pedons were selected based on the area of the depression in the south desert of Najaf province which located between °31 ^-54”2 and ° 29^-49 ”56 latitude north and °44 ^-29 ”40 and °42 ^-46 ”35 longitude east and represented by Al-Hayadia, Farea Alsalam and Om Al-Habara depressions to characterize and classify the soils of these depressions. A semi-detailed soil survey was conducted using free-lance soil survey method depending on the variance of the observed traits particularly topography, texture, soil colour and natural vegetation. Pedons were detected and morphologically described and a disturbed soil samples were obtained from each horizon for the purpose of conducting physical and chemical analyses, as well as undisturbed soil samples to study the micro-morphological characteristics. There was increase in the total clay content with depth in the pedons of depressions to the level that meets the conditions for the formation of Argillic clay horizon, which was confirmed by the results of micro-slices as the total clay content in the alluvial horizons increased than in the loss horizons. The outcome also indicated that there was increase in calcium carbonate content in all samplesand calcic horizon was formed in most of study pedons. There was decrease in salt content in all studied horizons (0.09-1.24ds.m^-1). The gypsum in the soils ranged between 1.55 to 13.38%.Current study results showed the Typic Calciargids in first and second pedons, and Typic Haploargids in the third pedon.