Pedosphere 28(4): 656--665, 2018
ISSN 1002-0160/CN 32-1315/P
©2018 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Description of Soil Evolution in Southern Mashhad City Using Jenny's and Johnson and Watson-Stegner's Conceptual Models
Alireza KARIMI1, Isa ESFANDIARPOUR BORUJENI2, Mohamad GHASEMZADEH GANJEHIE3
1Soil Science Department, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad 91779-48974(Iran)
2Soil Science Department, Faculty of Agriculture, Vali-e-Asr University of Rafsanjan, Rafsanjan 77188-97111(Iran)
3Soil and Water Department, Khorassan Rzavi Agricultural and Natural Resources Research and Education Center, Agricultural Research Education and Extention Organization(AREEO), Mashhad 91659-66416(Iran)
Corresponding Author:Alireza KARIMI
ABSTRACT
      Conceptual models are suitable for describing internal relationships of complex systems, including soil. We used conceptual models, the Jenny's and Johnson and Watson-Stegner's models to understand the formation and evolution of soil. We studied 20 pedons in granitic hilly lands, loessial piedmont, and piedmont plain in southern Mashhad, northeast Iran. These soils were characterized by high levels of gypsum, especially in the granitic saprolites, which suggested the importance of the wind in shaping the soil structure. Jenny's model is a developmental and equilibrium model, which only describes the state of the soil formation factors and considers that each bioclimatic zone has a specific climax soil. It focuses on the genesis of the surface soil and is not suitable for buried soils and paleosols. Johnson and Watson-Stegner's model describes soil as a product of progressive and regressive processes due to horizonation or haploidization. Progressive processes during the last interglacial cycle created a well-developed paleosol with an argillic horizon in all landforms, except the piedmont plain. Developmental soil up-building by aeolian addition led to gypsum enrichment of the granitic saprolite. Erosion decreased soil thickness and exposed the argillic horizon. The Last Glacial Maximum led to greater deposition of loess, covering the paleosol. Humidity was higher during the early Holocene than today, leading to the development of a Bk horizon. This horizon was preserved in the stable surfaces of granitic hilly land and in the loessial piedmont, but buried on the piedmont plain via the deposition of alluvial sediments. Jenny's model could be used for current soil formation factors, whereas Johnson and Watson-Stegner's model required morphological characteristics of pedons for interpretation.
Key Words:  landscape evolution,loess,progressive pedogenesis,regressive pedogenesis,soil formation model
Citation: Karimi A, Esfandiarpour Borujeni I, Ghasemzadeh Ganjehie M. 2018. Description of soil evolution in southern Mashhad City using Jenny’s and Johnson and Watson-Stegner’s conceptual models. Pedosphere. 28(4): 656–665.
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