Classification of some gypsiferous soils in Holy Karbala Province

Abstract

The soil pedons were selected along study transect across the study region in Karbala Province, representing different geological formations ,physiographic location and level of ground water . The main objectives of the study are to identify the gypsic horizons and classification of study soils. Soil pedons were exposed and described according the survey manual used in Iraq . Disturbed and undisturbed soil samples were taken from all soil horizons were taken for physical and chemical analysis . The results of morphological , physical and chemical studies indicate the following :- The studied soils show some differences in the morphological and development mainly within their horizon type , thickness and sequences due to the local conditions for each pedon and dry climatic condition causing to form the soil order of arid region (Aridisols) and two sub orders(Gypsids)and(Calcids) and five soil series.The studied soils did not show a specific pattern for soil fractions distribution with depth which reflect the weakness in activity of pedogenic processes responsible for the formation of illuvial clay horizons due to the effect of alluvial parent material and dry climatic condition . Sand was the dominate soil fractions followed by silt and clay. The results indicate , that most of the studied soils are unsaline (EC<4dS m-1) , but one pedon with moderate salt content .The content of gypsum minerals increase within the subsurface horizons in comparison to the surface and C horizons which indicate the formation of gypsic horizon in most of the studied pedons . While , other pedons show the formation of calcic horizon which indicate the activity of decalcification and calcification processes . This was indicated by the morphological features of both secondary gypsum and contents accumulations in the studied pedons which ranged from fine soft powder , crystals and hard nodules in sand size . These accumulation present either in filling form or as cutans on the inside voids walls .