A magnetic investigation along a NE–SW transect of the Yasouj Plain, southwestern Iran

Abstract

The magnetic susceptibility (χ) of soils varies with the slope position due to some factors such as texture, drainage class, and land use. Limited information is available about the magnetic susceptibility properties of semi arid regions of southwestern Iran. This study attempts to link χ and Fe oxides of the soils to landforms, soil characteristics, and land use (paddy and dryland soils) on the same parent materials. Ten representative pedons were taken along a NE–SW transect in different physiographic units in the Yasouj Plain. The results indicated that χ is determined mainly by topography and land use. In most pedons, the highest concentrations of poorly crystalline Fe (Feo) were observed in the top soil with different types of land use. Aquic condition in paddy soils seems the main cause for a significant decrease in the amount of Fed in the studied soils. Maximum concentration of pedogenic Fe (Fed) was noticed in more stable landforms with non-aquic moisture regime. Paddy soils exhibited higher Feo/Fed ratio values, suggesting that they have more poorly crystalline iron oxide phases than dryland soils. Magnetic measurements showed that the χ values of paddy soils were much lower (3.8 times) than those of dryland soils. The highest value of χ was found in the pedons located on plateau and piedmont plains and the lowest value of χ belongs to those that are located on hill and river lower terraces. A positive correlation was found between the frequency dependence of χ (χfd) and χ in paddy and dryland soils. Higher values of χfd were observed at soil surface than at deeper levels, suggesting a greater proportion of ultrafine grains.