Soil science
Mahvan Hasanzadeh Bashtian; Alireza Karimi; Adel Sepehr; Amir Lakziyan; Omid Bayat
Abstract
Introduction
Soils and landforms have a strong relationship and archive evidence of climatic and environmental changes. Alluvial fans are one of the most important landforms in arid and semi-arid regions of Iran. Climate changes in the Quaternary, especially in the late Pleistocene, had a significant ...
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Introduction
Soils and landforms have a strong relationship and archive evidence of climatic and environmental changes. Alluvial fans are one of the most important landforms in arid and semi-arid regions of Iran. Climate changes in the Quaternary, especially in the late Pleistocene, had a significant effect on the evolutions of alluvial fans in arid and semi-arid regions. Alternate of sedimentation and soil formation in alluvial are the consequences of periodic climate change. Organisms are one of the main factors of soil formation. Biological crusts are part of organisms that are abundant in dry lands and especially in alluvial fans; however, their role in soil formation has been less studied. Biological soil crusts by providing the suitable biological activity, effect on trapping of aeoilian materials and hydrological processes affect the soil formation processes. The chemical properties of the soil affect the catabolic capacity of the soil and it is very different among the different layers of the soil. However, few studies have addressed the effect of processes on soil microbial respiration during change and evolution and pedogenic state. The objectives of this research were to 1) investigate the evolution of soils along the gradient from upstream to downstream of the alluvial fan and 2) investigate the changes in microbial respiration in different layers of soil and the factors affecting it.
Materials and Methods
The studied area is an alluvial fan in Razavi Khorasan province, in the southern slopes of the Binaloud mountain range. The climate of the region is semi-arid and the soil moisture and temperature regimes are Aridic border on Xeric and mesic, respectively. Three soil profile in the upper, middle, and base part of the alluvial fan were described. Bulk and undisturbed soil samples were collected from various soil horizons for subsequent physical, chemical, and micromorphological analyses. In addition, the microbial soil respiration was measured in all horizons. The soils were classified according to Soil Taxonomy and World Reference Base methods.
Results and Discussion
Sequences of sedimentation and soil formation were observed in the soil profiles. Vesicular (V), argillic (Bt), argillic-calcic (Btk), calcic (BCk) and cambic (Bw) horizons were the diagnostic soil horizons of the studied soils. Soil profiles of the middle and base were Xeric Calciargids in the subgroup category of Soil Taxonomy; while soil profile of the apex soil was Xeric Haplocambids. In the profiles, a thin vesicular horizon (V) was formed under the desert pavement. Below the vesicular horizon, evidence of clay illuviation, pedogenic carbonate nodules, and calcium oxalates in roots were observed in thin sections. This evidence shows the role of biological crusts in the formation of these features. In the lower horizons of the profiles, pedogenic carbonate nodules, carbonates pendants and clay coatings were observed. It seems that the upper soil (vesicular and underlying Bt horizons) were developed in the more humid periods of the Holocene, and biological crusts also played a key role in the processes of calcification and clay illuviation. The argillic horizons in the lower layers were formed during the stable periods of the late Pleistocene. The irregular microbial respiration mainly indicated difference in microbial activities labile organic matter content. The argillic horizons had the lowest microbial respiration, due to decomposition of organic materials during soil formation. In contrast, soil respiration was the highest in surface and calcic horizons. It seems that preservation of organic materials by carbonate complication. However, it is suggested to investigate the carbon fractions in relation to microbial biomass in the studied horizons.
Conclusion
In this area, biological crusts and vegetation affected the formation of soil in the aeolian sediments of the Vk and AVk horizons and played a significant role in creating the Bt horizon in profiles 2 and 3. The study of landform profiles showed the formation of calcic and argillic horizons in the past climate, while the Bt horizon of the upper layers was formed in the current Holocene period. This form of the argillic horizon is slightly different from the soils of the Iranian region because these horizons have not been reported so far. It has been proven that there were humid periods in the Holocene, and it needs more studies at present. The study of soil microbial respiration in landform horizons showed that argillic horizons decreased the amount of microbial respiration, while it increased in classical horizons.
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.
