Document Type : Research Paper
Authors
1 phd student of gorgan university of Agricultural Sciences and Natural Resources, Iran
2 Professor., Dept. of Soil Science, Gorgan University of Agricultural Sciences and Natural Resources, Iran
3 Associate Professor., Dept. of earth Science, Golestan University , Iran
4 Associate Professor, Department of Soil Science, Gorgan University of Agricultural Sciences and Natural Resources
Abstract
Introduction: loess are a special type of silty soil with a porous structure and poor cohesion, and often contain silt with minor amounts of clay to fine sand . These characteristics make loess among the problematic soils in terms of engineering geology. problematic soils are observed in different parts of the world including Australia, Brazil, New Zealand, the United States and many areas of Iran. Some fine-grained soils are structurally unstable, that is, they are easily dispersed and are highly erodible. Hence, presence of such soils in engineering and Agricultural projects can cause great damage and financial loss. One of the most important influencing factors in the vulnerability of loess soils is the dispersion phenomenon. Dispersion or colloidal erosion is a physical-chemical process that often occurs in fine-grained soils containing clay particles. In general, dispersion phenomena occur when the shear stress induced by the flow exceeds the friction among particles, causing surface abrasion. Erosion can extend itself along a drying crack, settlement, hydraulic fracture, or other high permeability channels in a soil mass. Dispersive loess soil easily and quickly separates and disperses from each other in water with low salt concentration without any special mechanical stimulation. Climate and physicochemical characteristics are two important factors in soil dispersive. which affect the degree of soil dispersive. Climate affects soil development by influencing physicochemical characteristics. On the other hand, soil texture, clay content, porosity and Bulk density, pH and solubility of salts in soil are closely related to dispersive. Although, extensive researches carried out to determine the dispersion potential of the soils, affecting factors on dispersion phenomenon and validation of the soil dispersion tests, no comprehensive studies have been performed on The effect of climatic characteristics loess soils in golestan province. Therefore, the aim of this research is to investigate the effect of climate and physicochemical characteristics on soil dispersive.
Materials and Methods: This research was focused on loess soils of Golestan province. seven pedons were selected, sampled and described in different parts of the province. Climatic data was prepared and physicochemical and dispersive analyzes were performed on soil samples. The values of pH, electrical conductivity, equivalent calcium carbonate, cation exchange capacity and bulk density were measured. In order to study the degree of divergence, Sherrard's chemical test and pinhole test were performed.
Results and Discussion By investigating the amount of rainfall in different regions of the province, it was found that the loess soils of Golestan province are not in the same climatic conditions. The results showed that the climatic and physicochemical characteristics of the soils in interaction with each other had a significant effect on the evolution of the soil and the reduction of divergence in the studied soils. The highest amount of precipitation was in Ramyan and Minodasht region And these two regions had greater depth of soil and heavier texture than other pedons. The results of the pinhole test show these soils with intermadiate dispersion potential. While the results of the chemical test for most of the samples are non dispersive. According to the results obtained from the pinhole test, Minodasht and Sufian pedons with rainfall of 815.8 and 608.9 mm were completely non-divergent, and Hoten pedon with Aridic moisture regime and rainfall of 189.7 mm had the highest dispersion potential. In total, 30% of the horizons showed moderate dispersion. which were mostly in the Aridic moisture regime. The chemical test in this research also confirmed the presence of a small amount of sodium ion in the saturated soil extract, and only three horizons had the potential of chemical divergence based on the SAR level. From the results, it can be analyzed that the soil dispersion in this research is due to the physical nature of soil particles.
Conclusion: The review of climatic data and the results of physico-chemical tests showed the existence of direct coordination between the climatic and physico-chemical properties of the soil. So that with the increase of rainfall, the soil formation process increased. This means that in soils with xeric regime and high rainfall, the percentage of clay, organic matter, porosity and water retention in the soil has increased. As a result, the dispersion potential in these soils has decreased.
Keywords: Loess soils, Dispersive soil, Physicochemical dispersion, Pinhole test.
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