The Relationship between the Slope Hill and Bedrock with Some Soil Properties

Introduction Changes in soil properties depend on factors such as climate, topography, landscape features, altitude, parent material, and vegetation. The quantity and quality of soils obtained from different rocks (igneous, sedimentary and metamorphic rocks) depend on the minerals that make up the rock, as well as weather and other factors. Soil parent material is one of the primary and important issues in soil classification in terms of physical quality and also one of the most important effective factors in soil erodibility. The topographical factor of each region is one of the important and influential features on the soil quality of that region. The present research was conducted with the aim of understanding the spatial changes of soil properties in different slopes and different types of rocks. Material and Methods The studied area is located in Razavi Khorasan province in the cities of Mashhad, Chenaran, Sarakhs and Torbat-Haidarieh. The geographic location of the region ranges from 58 degrees and 52 minutes to 60 degrees and 40 minutes east longitude and 35 degrees and 38 minutes to 36 degrees and 25 minutes north latitude. This research was carried out on seven types of rocks: granite, Sarakhs paleogene limestone, Chenaran jurassic limestone, marl, shale, sandstone and ophiolite from relatively pure rocks of Razavi Khorasan province. In the present study, two factors of rock type and slope were investigated as effective factors of soil properties. Soil samples were taken from the surface layer (0-20 cm) and from three slope classes ie., less than 10%, 10-25% and more than 25%, as well as all soil samples from the southern slopes. Tree soil samples were taken from each slope and a total of 63 samples were taken and the samples were transfered to the laboratory for physical and chemical tests. In this study, the soil particle size distribution (texture) was measured by hydrometer method, organic carbon and calcium carbonate were determined by wet oxidation and titration with HCl 6 M, the mean weight diameter of soil aggregates and surface crust factor were calculated by related equations. To measure soil cohesion and penetration resistance were used pocket vane test and pocket penetrometer, respectively. Comparison of means was done through Duncan test in spss software. Results and Discussion The results showed that all the studied variables in different types of stones had a significant difference at the level of 1%. There was no significant difference in the variable of surface level in different slopes. Also, the variables of calcium carbonate percentage and saturated conductivity at 5% level had significant differences in different slopes. Other characteristics of soil, including percentage of organic matter, the mean weight diameter of soil aggregates, the number of drops impact, and soil cohesion and penetration resistance in different slopes had a significant difference at the level of 1%. Althoug the soil texture class was not significantly different in different slopes, the percentage changes of clay, silt and sand had a lot of difference along the slope. The highest and lowest parameters of organic matter percentage, Soil cohesion and penetration resistance were observed in granite and shale, respectively. The highest percentage of calcium carbonate was observed in Chenaran limestone (40.41%) and the lowest in granite (14.72 %). The mean weight diameter of soil aggregates was the highest in ophiolite (1.005 mm) and the lowest in marl (0.403 mm). The mean weight diameter of soil aggregates in the medium slope was significantly higher than the other two slopes. The parameter of the number of drops impact was the highest in granite (47.14 number) and the lowest in marl (27.70 number). The highest value of saturated conductivity variable was observed in marl rock and the lowest value was observed in Chenaran limestone. Conclusion The results showed that all the investigated variables had significant differences in different types of stones. Also, some of the investigated variables such as percentage of organic matter, percentage of equivalent calcium carbonate and the mean weight diameter of soil aggregates had significant changes along the hillside. As a general conclusion, given that the physical and chemical properties of the soil are partly under the influence of the parent material and the slope, and also with the presence of good geological information in the country, it can be suggested to provide suitable management solutions to prevent soil erosion and degradation by comprehensive examination of soil properties under different slope and types of stones.