Leili Neghadzamani; Mohammad Hady Farpoor; Azam Jafari
Abstract
Introduction: Genesis and development of soils are highly affected by soil forming factors and processes. Climate and topography (landform) are among the factors affecting weathering of parent material and genesis and development of soils in an area. Besides, various morphological, physical, and chemical ...
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Introduction: Genesis and development of soils are highly affected by soil forming factors and processes. Climate and topography (landform) are among the factors affecting weathering of parent material and genesis and development of soils in an area. Besides, various morphological, physical, and chemical properties, micromorphology, and clay mineralogy of soils at different geomorphic positions are usually affected by different soil forming factors including parent material and climate. The objectives of the present research were to study the effect of climate and geomorphology on physicochemical properties, micromorphology, and clay mineralogy of the soils in Rayen area, Kerman Province.
Materials and Methods: The study area starts from Hezar mountain elevations close to Rayen city (south east of Kerman Province) and extends to plateaus surfaces around Bam city. Quaternary and Neogene formations were found from geology point of view. Mean annual precipitation is in the range of 200-300 mm. Five landforms including rock pediment, mantled pediment, piedmont plain, plateaus, and valley were investigated during field work followed by topography, geology, and Google map studies in the area. According to 1:2500000 map provided by Soil and Water Research Institute, xeric and aridic soil moisture regimes together with mesic soil temperature regime were found in the area. Nine representative pedons were studied based on climatic regimes and different geomorphic surfaces. Pedons 1 and 2 were located on rock pediment with an aridic soil moisture regime. On the other hand, pedon 3 was located on the same surface, but with xeric moisture regime. Pedons 4 and 5 were also located on mantled pediment with aridic and xeric moisture regimes, respectively. Pedon 6 was located on piedmont plain and in the aridic moisture zone. Pedons 7, 8 (Plateaus), and 9 (Valley) were all in the aridic moisture zone. Physical and chemical properties, micromorphology, and clay mineralogy of soils were investigated and the soils were classified using USDA Soil Taxonomy (12th edition) and latest edition of World Reference Base for Soil Resources (WRB) systems.
Results and Discussion: Cambic, gypsic, argillic (or argic), calcic, and petrocalcic horizons were investigated during field and laboratory studies. Typic Haplocambids (pedons 1 and 2), Typic Calcixerepts (pedon 3), Typic Torriorthents (pedon 8), Calcic Petrocalcids (pedon 7), Typic Calcigypsids (pedon 6), Typic Xerorthents (pedon 5), Typic Haplocalcids (pedon 4), and Typic Calciargids (pedon 9) were classified using Soil Taxonomy (2014) and Gypsisols (pedon 6), Calcisols (pedons 3, 4, 7, and 9), Cambisols (pedons 1 and 2), and Regosols (pedons 5 and 8) Reference Soil Groups were determined using WRB (2015) system. Electrical conductivity increased from rock pediment toward valley and decreased from aridic toward xeric soil moisture regimes. Formation of argillic horizon in pedon 5 (Xeric moisture regime) was attributed to the climate of present time, but pedons 8 and 9 with aridic moisture regime could probably have experienced a climate with more available humidity for argillic horizon to be formed. Besides, petrocalcic horizon formation in pedon 7 was also attributed to a climate with more available humidity in the past. A buried soil (Btkb horizon) was determined in pedons 5 and 8 under the modern soil. Soil moisture regime change from aridic to xeric in rock pediment surface caused change of Aridisol to Inceptisol, but classification of soils in WRB system, was not affected. Secondary forms of calcium carbonate including powdery pocket, soft masses, and mycelium and secondary gypsum such as fine and coarse pendants were found during field studies. Calcite, gypsum, and clay coatings and infillings together with isolated gypsum crystals and gypsum interlocked plates were among dominant micromorphological pedofeatures investigated. Calcite coatings on aggregates and soil particles associated with clay coating prove the role of paleoclimate in soil formation. On the other hand, presence of manganaze nodules is an evidence of oxidation/reduction condition taken place in the xeric moisture conditions of pedon 5 (rock pediment). Illite, chlorite, kaolinite, and smectite were investigated in both rock and mantled pediments, but palygorskite was only found in mantled pediments. Climate also played a significant role in determining the source (pedogenic or geogenic) of clay minerals.
Conclusions: Results of this study clearly showed the close relationship among soil formation, topography (geomorphic surface) and climate. Soil physicochemical properties, micromorphology, clay mineralogy, and soil classification were highly affected by climate and geomorphology.
Mohammad Akbar Bahoorzahi; Mohammad Hady Farpoor; Azam Jafari
Abstract
Introduction: The optimum and sustainable use of soil is only possible with correct and complete understanding of its properties. The objectives of the present research were to study 1) genesis and development of soils related to different geomorphic surfaces in Kouh Birk Area (Mehrestan City), 2) Soil ...
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Introduction: The optimum and sustainable use of soil is only possible with correct and complete understanding of its properties. The objectives of the present research were to study 1) genesis and development of soils related to different geomorphic surfaces in Kouh Birk Area (Mehrestan City), 2) Soil classification according to Soil Taxonomy (2014) and WRB (2014) systems, and 3) physicochemical properties, clay mineralogy and micromorphology of soils.
Materials and Methods: Mean annual rainfall and soil temperature in the selected location are 153.46 mm and 19.6 oC, respectively. From geological point of view, the studied area is a part of west and south west zones and Flysch zone of east Iran. Soil temperature and moisture regimes of this part are thermic and aridic, respectively. Eight representative pedons on different surfaces including rock pediment, mantled pediment, Alluvial fan and Upper terraces were selected, sampled, and described. Routine physicochemical analyses, clay mineralogy, and micromorphological observations performed on soil samples. Soil reaction, texture, electrical conductivity, calcium carbonate, and gypsum were identified. Four samples including Bt horizon of pedon 1, Bk1 horizon of pedon 4, By2 horizon of pedon 5 and Bk1 horizon of pedon 7 were selected for clay mineralogy investigations. Four slides including Mg saturated, Mg saturated treated with ethylene glycol, K saturated, and K saturated heated up to 550 oC were analyzed. A Brucker X-Ray diffractometer at 40 kV and 30 mA was used for XRD analyses. Undisturbed soil samples from Bt horizon of pedon 1, Bk2 horizon of pedon 2, Btn horizon of pedon 3, By2 horizon of pedon 5, Bk1 horizon of pedon 7, and By1 horizon of pedon 8 were selected for micromorphological observations. A vestapol resin with stearic acid and cobalt as hardener was used for soil impregnation. Bk-Pol petrographic microscope was used for micromorphology investigations.
Results and Discussion: Due to the presence of argillic and petrocalcic horizons in rock pediment, soils of this surface were more developed compared to other landforms. High amount of CaCO3 (39.5%) was observed in pedon 4 on rock pediment geomorphic surface which is attributed to calcareous parent material. The presence of argillic horizon in this geomorphic position is due to the more available water of the past climate. The maximum salinity was observed in the mantled pediments. Calcic over gypsic horizons formed in pedon 7 on alluvial fan surface due to higher solubility of gypsum than calcium carbonate. Kaolinite, illite, chlorite, and palygorskite clay minerals were found in pedons 1 and 4 on rock pediment. Palygorskite in this position seems to be pedogenic, but kaolinite, illite, and chlorite are inherited from parent material. Mantled pediment and alluvial fan showed smectite, kaolinite, illite, chlorite, and palygorskite clay minerals. Pedogenic smectite in this position is probably formed from weathering of illite and chlorite. On the other hand, palygorskite stability decreased in mantled pediment surface. This is the reason why smectite was the dominant clay mineral in this landform. Clay and calcite coatings were investigated in Bt horizon of pedon 1 (rock pediment). Coatings and infillings of calcite in Bk2 horizon of the same geomorphic position caused a calcic crystallitic b fabric. A diffused clay coating due to the presence of Na in Btn horizon of pedon 3 in rock pediment was observed. Micromorphological observations of By2 horizon in pedon 5 (mantled pediment) showed gypsum interlocked plates and gypsum infillings. Interlocked plates formed due to re-solubility of gypsum crystals. Micro spars and infillings of calcite are among dominant pedofeatures found in Bk1 horizon of pedon 7 (alluvial fan geomorphic surface). A calcic crystallitic b fabric and Primary calcite mineral were also observed in this pedon. Release of Ca from calcareous parent material caused Ca+2 to SO4-2 ratio to be increased which could be a probable source of gypsum formation. Results of the study showed that more and less developed soils formed on rock pediment and upper terrace geomorphic surfaces, respectively. Illuviation of clay, gypsum, and CaCO3 together with formation of cambic, calcic, petrocalcic, gypsic, argillic, and natric horizons were among the dominant pedogenic processes in studied soils. Paleosols containing Bt horizons were only observed on rock pediment geomorphic surface. Kaolinite, illite, chlorite, and palygorskite clay minerals were observed in almost all surfaces. Smectite was not discovered in rock pediment, but was only investigated in mantled pediment and alluvial fan which could be attributed to higher available moisture of formation time in these surfaces. Secondary calcite and gypsum caused stability of pedogenic palygorskite in soils under study. Micromorphological observations proved the presence of clay and calcite coatings, calcite and gypsum infillings, and gypsum interlocked plates. Gypsum pedofeatures were not observed in rock pediment, but clay and calcite pedofeatures were only found. On the other hand, clay and calcite pedofeatures were not observed in upper terraces and gypsum pedofeatures were the only features determinded in this position.
Conclusion Results of the present research showed that difference in soil characteristics is highly affected by geomorphology.
