GENESIS, DEVELOPMENT, AND CLASSIFICATION FOR SOME SELECTED SOILS AT KURDISTAN REGION, NORTH OF IRAQ

H K Ismail,M A Fayyadh

doi:10.36103/ijas.v52i6.1491

Abstract

The study area was located in the North of Iraq. Five sites were selected that have formed from the limestone parent material. One pedon dug in each site and was divided into a number of horizons. Thirty-five soil samples were collected for physical and chemical analyses. The climate of study sites were similar to the Mediterranean Sea climate which is hot dry in summer and cool humid in winter. The mean of annual precipitation, varies from one site to another. Studied soils classified as Mollisols, Inceptisols, Vertisols, and Aridisols. Study soils were relatively high clay content and its content at the surface horizons is lower than it at subsurface horizons, and soil texture was ranged between clayey to loamy, the high value for clay content indicates to soil development. Fine clay/Coarse clay ratio showed that the pathway of fine clay similar to the pathway of total clay. CEC values increased with increasing clay. Organic matter was high in the surface horizons and decrease with depth. The following pedogenic processes occurred in study soils loss, gain, leaching, illuviation, eluviation, alkalization, humification, lessivage, desalinization, calcification, decomposition, and synthesis.

Highlights

Pedogenic processes, leaching processes, are essential to soil formation; the climate is of paramount importance in this regard, rainfall and temperature (3)
This study aimed to explain soil formation depending on the pedogenic processes, specify soil development, and classification of study soil according to the key to soil taxonomy as adopted for use by USDA
The values of CEC ranged between (10.3- 27.7 Cmolec kg-1) and the Cation exchangeable capacity values increased with increasing clay content and the highest value was (27.7 Cmolec kg-1) in pedon (5) at Wermawa site in (Bk1) horizon which has clay content (625.3 g kg-1), and this may be due to the lessivage process that was happened in this pedon with a high amount of clay content, and the clay particles are small size, that has a high specific surface area, can be adsorbed high amount of cations on its surfaces, in turn, causes high CEC values whereas the lowest value of CEC was (10.3 Cmolec kg-1) found in the surface horizon (Ap) in pedon (3) at Gerderash site which has clay content (184.8 g kg-1)

Summary

Introduction

Leaching processes, are essential to soil formation; the climate is of paramount importance in this regard, rainfall and temperature (3). Soil features are formed by pedogenesis acting on anthropogenic materials and a wide variety of (bio) geochemical processes are involved in their formation, including the bacterial breakdown of the organic material, as well as adsorption, precipitation, humification and mineralization (22). The accumulations of clays and oxides reflect the stage of pedogenic development (6). Changes in the weathering index with depth commonly are gradual or continuous, steady and systematic for homogeneous parent rocks, reflecting continuous leaching of elements as weathering progresses on initially homogenous parent material, similar patterns have been reported in at least some instances of saprolitic profiles developed on deformed gneisses and schists (23). Illuviation of clay is considered to be an important pedogenic process in soil formation. Decomposition of organic matter and weathering of primary minerals are possible sources of exchangeable cations

Objectives

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Results