جستجوی مقالات مرتبط با کلیدواژه "soil genesis" در نشریات گروه "کشاورزی"

Changes of soil carbon is one of the most important indicators showing the climate impacts on the soil genesis. Soil organic carbon management requires knowledge of its amount and the effective factors. In the current study, the distribution of soil properties especially soil organic carbon were studied in 76 soil profiles consist of different climatic zones arid (Alborz province), semi-arid (Alborz and Qazvin province) and semi-humid (Guilan and Mazandaran province) and humid (Mazandaran province) with aridic, xeric and udic moisture regimes and thermic and mesic temperature regimes. Changes in climatic parameters cause changes in species diversity in the ecosystem and ultimately effect on various forms of carbon, especially soil organic carbon. One of the most important climatic factors in this study is the temperature that increasing the soil temperature in arid and semi-arid regions compared to the two wetter regions causes intensification of mineralization and as a result, soil organic carbon is reduced. The results showed that the amount of organic carbon in the studied soil decreases with increasing depth and the average amount of organic carbon in Mollisols was higher than Alfisols= Inceptisols > Entisols > Aridisols. The general results of this study showed that increasing the parameters of soil electrical conductivity (salinity), soil acidity and clay content have a negative effect, while increasing the parameters of cation exchange capacity and silt content have positive effects on soil organic carbon content.

The soils developed in the context of the landforms and they evolve under influence of similar factors. Therefore, the identification of soil-landform relationship is the first step for the soil survey, pedology and paleopedology and geomorphology researches. Afghanistan is located between arid environments of Iran and cold and humid highlands of Himalaya. Due to special social and political conditions, little information existed on the soils of Afghanistan. Alluvial fans are the common land forms in arid environments which usually are archive of soil formation and sedimentation periods in the past. Landform assemblage in southern Herat (alluvial fans to piedmont plan and flood plain), could provide suitable information on the soil landform relationship in arid areas of Afghanistan. This study was the first pedology research in Afganistan. The objectives of this research was to identify the soils along a transect from alluvial fan to flood plain of Hariroud River, determine the clay mineralogy and micromorphological features of the soils and finally determine the soil evolution in the study area.
Material and The study area located in southern Herat between longitudes of 34° 20’ 21” to 34° 25’ 33” E and latitudes of 43° 20’ 21” to 43° 25’ 33” N. The mean annual precipitation and temperature of the study area are 250 mm and 16. 1 ºC. A transect from an alluvial fan from Sefidkouh Mountain to flood plain of Hariroud River were selected. The geomorphic surfaces along the studied transect were alluvial fan, alluvial fan-piedmont plain transition, saline and non-saline piedmont plain and flood plain. Five representative soil profiles along a transect of Alluvial fan, intermediate Alluvial fan– piedmont plain (lowland), piedmont plain and flood plain were described and sampled. Undisturbed samples were taken for thin section analysis and recognizing pedofeatures. The mineralogy of the clay fraction was determined using X-ray diffraction method. Calcic-argillic (Btk) horizon was the most developed horizon which occurred in alluvial fan. Alternation of paleosol (Btk horizon) and undeveloped coarse-alluvial layers indicated alternation of soil formation and sedimentation periods in the past. Regarding the argillic horizon development conditions, the Btk is the relict features from a wetter climate in the past. Similar soils were observed in arid regions of Iran. The gleization and few secondary carbonates and salt accumulation was the pedogenic processes in other landforms. Bw horizon was common horizon in other studied soils. In Alluvial fan – piedmont plain transition geomorphic surface, due to depression in the landform, salt accumulated in the surface soil and electrical conductivity reached to 40 dS/m. However, salic horizon because of limited thickness was not identified. In non-saline piedmont plain and floodplain geomorphic surfaces, soils showed oxidizing and reducing conditions and consequently gleyic color pattern. Maximum EC (49 dS/m) was occurred in saline piedmont plain surface. The results showed that electrical conductivity values increased from alluvial fan toward lowland positions. Besides, fine soil textures were found in downward positions. The Soil Taxonomy classification of the soils were Typic Calciargids in alluvial fan, Aquic Haplocombids in alluvial fan-piedmont plain transition, non-saline piedmont plain and flood plain as well as Typic Haplocambids in saline piedmont plain. Chlorite, illite, palygorskite, smectite, and kaolinite were the main clay minerals. Chlorite and illite were inherited from parent materials. Micromorphological observations proved clay coating on carbonate nodules and coarse fractions in Btk horizon. The alternation of secondary carbonates on clay coating is the evidence of polygenetic soils and change of from wetter to drier climate. Also, iron oxides nodules in Btk horizon indicated suitable weathering conditions during clay accumulation. Lenticular gypsum was observed in the soil in saline piedmont plain geomorphic surface. Coating and hypocoating of iron oxides identified in flood plain soil. Results of this research showed the role of geomorphic processes and climate change in the soil evolution in the area. The results of this study indicated the progressive and regressive processes which are preserved in the soil of alluvial fan. The Btk horizon in alluvial fan represent wetter condition than today. The morphological, mineralogical and micromorphological features of the soil in the alluvial fan were similar to correspondence soil in arid environments of Iran. Continuous sedimentation in the piedmont plain and flood plain prevent the soil development in these landforms.

Soil carbon changes is one of the most important indicators impacts of climate change impacts on soil genesis. Study of soil carbon, including organic and inorganic carbon (carbonates) and its impact on other soil characteristics in different climates, is essential for the proper management of soil carbon on a global scale. It is too important the balance between different parts of carbon sources in the environment. In current study, organic and inorganic carbon complex with primary particles were studied in 9 profiles a climosequence including three climates arid, semi-arid and semi-humid with typic aridic, dry xeric and typic xeric moisture regimes and mesic and thermic temperature regimes. Results showed that the amount of organic carbon in all three components decreases with increasing depth and also clay component has more organic carbon content in all depths compared with other components of soil. Contrast to organic carbon, inorganic carbon content is lower in surface horizon compared with the subsurface in all three components of particle size and increases with increasing depth. The avearage of organic carbon components of particle size in three studied regions showed that the following trend clay (1.1%) > silt (0.68%) > sand (0.23%), while inorganic carbon in the soil with trend silt (14.41%) > sand (12.11%) > clay (8.14%).

Soil genesis and evolution studies are based on well understanding of geochemical processes involved in pedogenic processes and formation of soil. Parent materials are main factors controlling soil properties in arid and semiarid regions. In this study, physicochemical and geochemical properties of 6 selected soil profiles developed on basalt rocks along arid (Eshtehard), semiarid (Qazvin) and semihumid (Roodbar) climosequence representing three different climatic zones were investigated. The total content of Si, Al, Fe, K, Mg, Ca, Na, Mn, P, Zn, Cl, Cu, Pb, Mo and Cd of all soil horizons were compared to parent rocks to reveal the role geochemical composition of rock on total concentrations of these elements in soil. Enrichment/depletion patterns of elements were assessed using Ti as reference element. The studied elements exhibited different enrichment/depletion patterns. In soils of arid region, the role of parent material and lithogenic properties in concentration of elements were greater than other areas and the content of these elements due to lower weathering and leaching were closer to the parent rock. While, in more humid climates pedogenic processes were more intensive and enrichment/depletion patterns of elements showed states that are more progressive. Distribution of some studied elements such as magnesium, calcium, iron and copper were significantly affected by soil forming process and the parent material affected some other elements such as sodium, aluminum, silicon, phosphorus, chlorine, manganese, molybdenum, cadmium and lead. In general, part of the difference in the concentrations of elements can be related to their chemical nature and the mobility of some elements, and some part to rapid weathering of parent materials affected by bioclimatological changes.

Loess deposits on the slopes of Alborz mountain in northern Iran represent the most important geoarchive of climate change in the region and provide an important link between loess deposits in Southeastern Europe and Central Asia. These deposits are so important because of preserving palaeosols to reconstruction of past soil formation processes and consequently, climate condition on formation time. Therefore, this study for palaeopedological investigation on three loess-palaeosol sequences (Agh Band, Mobarak Abad and Neka) to reconstruction of past pedogenesis processes was done along a climosequence in northern Iran. Three loess-palaeosol sequences including Agh Band, Mobarak Abad and Neka sections were studied in Golestan and Mazandaran provinces in northern Iran. Agh Band section is located in the westernmost part of the Northern Iranian loess plateau. The section at Mobarak Abad is exposed in a deep road cut located on the northernmost ridge of the Alborz Mountains. Neka loess-palaeosol sequence located on the top of a deep Iimestone quarry about 10 km east of Neka. Soils sampling was done in several field campaigns in spring 2012. After soil sampling and field description, some physic-chemical properties was analyzed. Six modern soil profiles (for comparison) were dug along this climosequence which classified as Entisols, Inceptisols, Mollisols and Alfisols. Results of physico-chemical analyses show silt particles were dominant particle (more than 50 percent) in the loess-palaeosol sequences and modern soils which confirmed aeolian source of loess deposit. Clay content increased from Agh Band to Mobarak Abad and Neka section while silt content decrease which it may reflected weathering processes of clay and/or it’s translocation and the distance from loess source. Carbonates amount were variant in different horizon (about 15-20 percent) which reflected climate condition and pedogenesis activity. Results shows one preliminary soil formation stage in Agh Band section whereas Mobarak Abad shows about 5 periods and Neka at least 4-6 periods in different pedogenesis levels and soil develop degrees. Soil development and variation in soil horizons increase (in both palaeosols and modern soils) along of climosequence (from dry to moist region) that reflected pedogenic activity which has direct relation with climate. These results show the modern climate gradient (especially for precipitation) existed during the time and climate change control amount and intensity of soil formation processes.

The origin and micromorphology of three selected pedons in mountainous Aq- Emam area (in northeast Golestan province) were investigated. The objectives were to examine 1) physico-chemical and micromorphological characteristics of studied pedons developed in different geomorphic positions and 2) evaluate the relationship between them with underlying limestone and loessial sediment as preassumed parent materials. Our results showed that the shallow soils developed on steep upslope have a cambic horizon as a main subsurface diagnostic horizon. In contrast, more thick and clayey soils developed on sloping areal have an argillic horizon with decalcified solum indicating more eluviation due to more landscape stability. Cyclical erosion and deposition which occur on colluvial foot slope must be responsible for superimposed pedo-sedimentary complexes in this position. Mass-balance calculations and geochemical ratios show that the soils in sloping midslope have a loessial nature due to windblown source and geomorphic processes. Erosion keeps these additions to some extent from appearing on the steep upslope thus these soils have a polygenetic nature derived from loesses and limestone’s insoluble residues. In brief, we can conclude that residual origin of soils formed on limestone rocks is controversy especially for those with deep solum and we should consider other possibility of material addition to soil such as eolian contamination and geomorphic processes.