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 ...
Read More
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.
Taymour Eslamkish; Milad Kurdi
Abstract
Introduction: Peat is an organic soil which is formed by the accumulation of decayed vegetative matter that have formed in areas of poor water drainage. The mineral components of peat are derived from inorganic matter contained in sediments and by adsorption from groundwater. The inorganic (mineral) ...
Read More
Introduction: Peat is an organic soil which is formed by the accumulation of decayed vegetative matter that have formed in areas of poor water drainage. The mineral components of peat are derived from inorganic matter contained in sediments and by adsorption from groundwater. The inorganic (mineral) fraction of peat usually includes only 2–10 Percent of its dry weight, but for highly decomposed peats can increase to about 60 percent of dry weight. Thin sections of peat reveal detailed information of composition, structure, fabric and particularly pore properties which influence water retention and movement. Peat is a concentrated form of soil organic matter which has environmental, industrial, agricultural and medical uses that range from sustaining the productive capacity of agricultural land. This study has been focused on micromorphological and mineralogical properties of Suteh peat swamp forest (PSF) in Golestan province, north of Iran. Golestan province is the third largest cereal producer in Iran but scarcity of water and salinity are most important major problems in this area. This area has been covered by almost 400,000 hectares of forests. Suteh PSF has been chosen as a swamp that contains organic and inorganic matters. As the inorganic composition of peat varies considerably from region to region, study of mineralogical and micromorphological of Suteh PSF can be useful in order to identification of Golestan province peat swamps. Since the early 1990s, micromorphological studies have become increasingly popular in the analysis of lakeside settlements. The evaluation of soils considers thin-section observations, macromorphological features, and laboratory data. Micromorphological analyses allow the characterization of natural and anthropogenic sediments, which in turn enables the determination of sedimentary processes and depositional environment.
Materials and Methods: This study was carried out in April 2014. The samples were collected from zero to 40 cm depth of swamp areas, within a 10 cm radius. At each sampling station, peat samples were collected with a trowel. The area included the north side of the Alborz Mountains and extended northward to the township of Gorgan. The altitude was approximately 950–2000 m a.s.l. According to the Gorgan Natural Resources Bureau report, Suteh is temperate to semi-arid on the Emberger climate diagram. To achieve the purpose, samples were dried and prepared based on standard methods. These studies were carried out using polarized microscope on thin sections and polished section at the Mineralogy Laboratory of the Amirkabir University of Technology.To prepare thin sections for microscopy studies, samples with polyester, cobalt oxide and hardener have been combined. Polyester formed the matrix of the section and hardener (HCl + H2O2) has been used to reduce a hard time getting. Cobalt oxide has been used as a catalyst between them. The samples have been kept tight in special containers. Due to the presence of organic matter, much time was needed to harden them. The samples were dried and tightened for 20 days. Then, the samples were polished by various polishers (No. 400, 600, 800, 1000 and 2000). After that, they were polished for 20 minutes by the suspension of alumina (Al2O3 + H2O).
Results and Discussion: The coarse material that formed groundmass were composed of quartz, muscovite, orthoclase, calcite, opacity pyroxene biotite and opaque minerals. Some flakes of muscovite, pyroxene and biotite showed weathering. Fe–Mn components were most common in opaque minerals. Quartz crystals were seen in abundance in most sections. Weathered surface of orthoclase was seen in some sections. The large biotite crystals were seen at different sections with pleochroism light brown to dark brown. Root and other organ residues in varieties states of decomposition were observed in some sections. Fragments of organ and tissue residues were rather few and found mostly in the surface of Suteh PSF. For detailed assessment of opaque minerals, one of the grains was selected and analyzed. The weathering of minerals showed the normal stability trend, i.e. quartz >muscovite>biotite. Biotite loses its pleochroism and alters first to a mica-vermiculite interstratified clay mineral. Polished sections study showed Fe components were the major and dominate in the sections.
Conclusions: Thin sections results showed the samples contained quartz, orthoclase, muscovite, biotite, calcite, opacity pyroxene and opaque minerals. Polished sections results revealed that Fe components were most common in opaque minerals in the sections. Micromorphological study showed root and other organ residues in Suteh PSF that this showed this soil composed of a mixture of organ residues and organic material.
M. Zarinibahador; - K. Nabiollahi; M. Norouzi
Abstract
Introduction: Spatial variation of soil properties is significantly influenced by numerous environmental factors such as landscape features, including position, topography, slope gradient and aspect, parent material, climate and vegetation. Soil properties vary spatially in south- and north-facing hill ...
Read More
Introduction: Spatial variation of soil properties is significantly influenced by numerous environmental factors such as landscape features, including position, topography, slope gradient and aspect, parent material, climate and vegetation. Soil properties vary spatially in south- and north-facing hill slopes. This factor (different slope aspects) can affect the distribution of soil organic matter, the presence or absence of a layer, pH, nutrient levels, soil mineralogical and micromorphological properties. Topographic factors such as the orientation of the hill slope and the steepness of the slope affect microclimate, vegetation establishment, water movement and erosion. Aspect and slope control the movement of water and materials in a hill slope and contribute to differences in soil properties. Temperature, precipitation and climate vary with elevation and influence pedogenic processes. Accelerated rates of weathering and soil development were found to occur in soils on south-facing slopes. Slopes with a south aspect are dominated by stone and bare soil patches, while slopes with a north aspect are dominated by biotic components. Northern slopes have higher productivity and species diversity compared to Southern slopes. Slope aspect has a significant effect on the composition, species richness, structure and density of plant communities, differed significantly between North- and South- facing slopes.
Materials and Methods: In the present study, the effects of two slope aspects on some soil properties and soil evolution was investigated in Northern Rostam Abad region in the Guilan Province. Five profiles in Southern hill slope(South-facing hill slopes) and five profiles in Northern hill slopes(North-facing hill slopes) with 40% slope and same parent material (basaltic andesite) and same plant cover were dug. The elevation of two slope aspects was 240 meters from the sea level. Average annual temperatures and precipitation are16 degrees centigrade and 1359 mm, respectively. Thus, the soil moisture and temperature regimes are udic and thermic, respectively. The physical and chemical analysis were carried out on soil samples including particle size distribution, bulk density, pH, organic carbon, total nitrogen, available phosphor and cation exchange capacity. This study was done in a completely randomized design several observational with five replications. The total of 34 soil samples were collected in the two slope aspect of the profile and all samples were tested and statistical analyzed. For the micromorphological study, thin sections were prepared from undisturbed samples. The samples were impregnated with polyester resin and later sectioned. The thin sections were prepared and analyzed in petrographic microscope equipped with polarized light.
Results and Discussion: The results of multivariable analysis of variance (MANOVA) and Hotteling's T2 showed that there is significant different in soil properties between two hill slopes(p≤0.01). Also, the results of t-test showed the values of pH, content of sand, sand to clay ratio and available phosphorous significantly was higher in Southern hill slope in comparison with Northern hill slope(p≤0.01). Whereas, clay content and cation exchange capacity significantly were higher in Northern hill slope in comparison with Southern hill slope(p≤0.05). Also observed micromorphological studies showed biological activity was stronger in Northern hill slope in comparison with Southern hill slope. Properties observed in thin sections of Northern slope aspect include fungal hyphae, spherical and ellipsoid excrement of microorganisms in root residual (related to oribatid mites) which indicated stronger biology in Northern slope aspect soils as compare to Southern slope aspect soils. Also, more accumulates* of clay inside voids, nodules, fragmented of coating of well-oriented, micro laminated, reddish-brown clay, chamber voids in Northern slope soils toward Southern slope soils were observed. B-fabricobserved in Northern hill slope soils is stipple speckled in surface horizons and in subsurface horizons is grano-striated and stipple speckled and b-fabric observed in Southern hill slopes soils in surface horizons and subsurface horizons is stipple speckled.
Conclusion: Higher content of clay, Cation exchange capacity, Accumulation of clay in pores, Fragments of clay coating (papule), chamber pores, Fe/Mn oxide nodule and micro-laminations in Northern hill slope and higher values of pH, higher content of sand, sand to clay ratio and available phosphorous, lithorelict in Southern hill slope showed that weathering was higher in Northern hill slope in comparison with Southern hill slope. Generally, Southern hill slope had less developed soils (Entisols and Udorthents great group) and Northern hill slope had high developed soils (Alfisols and Hapludalfs great group).
