Spatial variability of soil erodibility associated with lithology and topography

Document Type : Research Paper


1 Department of range and watershed management, Faculty of Natural Resources and Environment, Ferdowsi University of Mashhad, Mashhad, Iran

2 Department of soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran


Today, water erosion is considered one of the most important forms of nature destruction, and the problems caused by it are inseparable problems of the country's watersheds. Among the numerous environmental factors affecting soil erodibility, lithology, topography and climate factors are the most important factors affecting soil erodibility. The purpose of this research is to investigate soil properties including number of drops impact (NDI), mean weight diameter of soil aggregates (MWD), soil penetration resistance (PR), soil cohesion (COH), saturated conductivity (Ks) and soil erodibility index (K). Therefore, six rock types (granite, limestone, ophiolite, shale, marl and sandstone) were selected in Razavi Khorasan province and sampling was done in three slope classes 0-10, 10-25 and more than 25% in 2021. In order to compare soil erodibility in similar rocks in different climates, limestone was selected in Tabas city (dry climate). The results showed that the average soil erodibility index and other indices have a significant difference (P<0.001). The results of measuring soil erodibility index in different slopes showed no significant erodibility index in three slope classes (sig=0.893, p<0.05). The comparison of the average soil erodibility in different climates in rocks similar to Paleogene limestone with a value of 0.83 in Tabas limestone and 0.96 (ton ha h / ha MJ mm) sarakhs limestone showed that the average soil erodibility in different climate has a significant difference (sig=0.023, p<0.05). The results of measuring CSEI index showed that the highest amount of reduction in erodibility reflected by this index is in granite with a value of 64% and the lowest value in shale with a value of 25%.


Main Subjects




Soil erosion is a process in which soil is separated from its main bed and transported to another place by a transport factor. Soil erodibility is a main feature of soil properties that shows the sensitivity of soil to erosion and depends on various factors. One of the factors affecting soil erodibility is the slope of the land, which can directly or indirectly affect soil erodibility. The main purpose of this study is to investigate the changes in soil erodibility using the EPIC method and the physical properties affecting it in different types of rocks in two provinces of Razavi Khorasan and South Khorasan in three slope classes and to compare at least one of these types of rocks in two different climates.

Material and Methods:

 The studied area is located in two provinces of Razavi and South Khorasan in the cities of Mashhad, Chenaran, Sarakhs, Torbat-Hydriye and Tabas. The geographical location of the region in Razavi Khorasan province is from 58 degrees and 52 minutes to 60 degrees and 40 minutes’ north longitude and 35 degrees and 38 minutes to 36 degrees and 25 minutes’ east latitude, and in Tabas city, the studied area is from 33 degrees and 43 minutes to 33 degrees and 46 degrees’ north longitude and 56 degrees 33 minutes to 56 degrees 37 minutes’ east latitude. In this research, seven types of granite, Paleogene limestone, Jurassic limestone, marl, shale, sandstone and ophiolite were selected from the relatively pure rocks of Razavi Khorasan province, and one Paleogene limestone was also investigated to compare the difference in erodibility in different climates in Tabas city. Soil samples were taken from the surface layer (0-5 cm) and from three slope classes: less than 10%, 10-25% and more than 25%, as well as all soil samples from the southern slopes. Three soil samples were taken from each slope and a total 72 samples were taken and analyzed in the laboratory for physical and chemical properties. The sampling of this research was done in the summer of 2021 and the proposed tests were done in March 2022 in the soil science laboratory of the Faculty of Natural Resources of Ferdowsi University. 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, mean weight diameter of soil aggregates and Surface crust factor were calculated by related equations. Soil Cohesion and Penetration Resistance were measured by pocket vane test and pocket penetrometer, respectively. Comparison of means was done through Duncan test in SPSS software.

Results and Discussion:

A factorial test was conducted with a completely random design for the investigated variables in different rock types and its results showed that the lithology factor for all variables has a significant difference at the level of 1% (p<0.001). The soil erodibility factor also has a significant difference at the level of 1% in different rocks. The soil erodibility factor in different slopes has no significant difference. The soil erodibility in Ferns Paleogene limestone with an average of 0.96 (t ha h ha-1 MJ-1 mm-1) is 13% higher than the average soil erodibility in Tabas Paleogene limestone with a value of 0.83 (t ha h ha-1 MJ-1 mm-1) and these values in two Arid and semi-arid Climate are significant at the level of 5%.


 Since soil erodibility is affected by various factors, it requires spending considerable time and money. Finding easily accessible parameters can save a considerable amount of time and money, especially when extensive samples are on the agenda. In this research, as there is a very good relationship between the soil erodibility and rock type, by completing the research on the major geological formations in the country, the rock type, which has a good database in the country, can be used as an easily accessible parameter to determine the soil erodibility level or limits.


Keywords:  CSEI Index, Erodibility, EPIC Model, Lithology, Soil indicators, Soil Erosion

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