JWSS - Journal of Water and Soil Science

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Magnetic susceptibility (χ) measurements are widely used for the evaluation of soil profile development. Fourteen soil profiles were studied in a relatively wide range of climatic conditions in Fars Province. Citrate-bicarbonate-dithionite (CBD) extraction and micro CT-Scan images were used to evaluate the source of magnetic susceptibility. The results showed that soil samples lost 23 to 91 percent of their magnetic susceptibility after CBD extraction (χCBD), reflecting differences in the source (pedogenic or lithogenic) of magnetic susceptibility. Greater values of the decrease were noticed mostly in well developed soil profiles as well as in soil surface. 22 to 89% of the decrease was observed in frequency dependence of magnetic susceptibility (χfd) after CBD extraction. A significant positive correlation (P<0.01) was obtained between χCBD and χfd in the soil studied. Micro CT-Scan images with a spatial resolution of 33 µm showed lithogenic magnetic Fe oxide (magnetite) grains.

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Topography and land use are among the most important factors affecting the soil formation. Chemical forms of Fe and magnetic susceptibility (&chi;) are widely used for the evaluation of soil development. This study was conducted in order to determine the effect of these factors on &chi;. A toposequence was selected in Madvan Plain, Northern Yasouj. Nine soil profiles (paddy and dryland soils) were dug and sampled from diagnostic horizons. Magnetic susceptibility was measured by Bartington Dual Frequency, MS2 Meter at frequencies of 0.46 and 4.6 KHz. Results indicated that less amounts of &chi;, frequency dependence of &chi; (&chi;fd%) and CBD extractable Fe (Fed) (3.1, 2.6 and 2.7 times, respectively), and more quantities of oxalate extractable Fe (Feo) and Feo/Fed ratio (5 and 7.2 times, respectively) were measured in paddy soils. The highest value of &chi; was observed in pedons located on plateau and piedmont plains, and the lowest belonged to those located on river terraces with aquic conditions. Compared to paddy soils, &chi; enhancement at soil surface was greater (17%) in dryland soils. A positive correlation existed between &chi; and some soil characteristics such as Fed, clay content and &chi;fd%.