Saturday, 15 July 2006

Distribution of Magnetic Susceptibility in Kohgilouye Boyerahmad soils, Southwestern Iran.

Hamidreza Owliaie, Yasouj Univ, Dept. of Soil Science College of Agriculture, Yasouj, Iran, Richard Heck, Univ of Guelph, Dept of Land Resource Science, Guelph, ON N1L 1M4, Canada, and Ali Abtahi, Shiraz Univ, Dept of Soil Science, College of Agriculture, Shiraz, Iran.

The magnetic susceptibility (א) was examined for 14 pedons in a relatively wide range of climate and drainage class of Kohgilouye Boyerahmad province located in southwestern Iran. The elevation of the province varies from 500 m above sea level in southwest to 4409 m above sea level in northeast of the province. Precipitation ranges from about 330 mm in southwest to 1185 mm in southeast of the province. Mean annual temperature ranges from 10.5 C in southeast to 23 C in south west of the Province. According to Soil Moisture and Temperature Regime Map of Iran the soils comprise xeric, ustic and aridic-ustic soil moisture regimes along with mesic, thermic and hyperthemic temperature regimes. Soil χ was considered both on air-dry basis (א a) and minerogenic basis (removing of mobile diamagnetic materials such as carbonates and gypsum) (א m). Soil Fe was characterized by selective dissolution according to total (lithium tetraborate fusion), pedogenic (citrate dithionite) and poorly-crystalline (ammonium oxalate) forms. Alfisols of the eastern and northern parts of the province contained larger concentrations of pedogenic Fe minerals (up to 60 g kg-1on minerogenic basis, and 70% of total Fe), and of poorly-crystalline (up to 6 g kg-1) Fe, than did the Inceptisols of the southern part. Soil MS (אlf) ranged from 5 to 120 x10-8m3kg-1, with the greatest values being observed in A compared with B horizons, and in Alfisols compared with other soils. Pedogenic enhancement of אlf appeared to be related to the preferential leaching of diamagnetic material (primarily carbonates), as well as to the weathering of primary paramagnetic minerals and neoformation of antiferromagnetic minerals. The frequency dependence of MS (אfd), reflecting the presence of ultrafine superparamagnetics, followed similar trends as א. Soil samples lost 32 to 93 percent of their χm and 0 to 92 percent of frequency dependent susceptibility (אfd) due to citrate-bicarbonate-dithionate treatment respectively, reflecting differences in the source (pedogenic or lithogenic) of magnetic susceptibility. Sequential heating of well-drained samples, from 25 to 500C, resulted in enhancement of א (average of 21%), attributed to the conversion of antiferromagnetic minerals to ferrimagnetic minerals; between 500 and 700C א typically decreased (average of 15% below original). The אfd of well-drained soils also increased by an average of 5.3 percentiles by 700C. Soils with restricted drainage (gleysolic) exhibited lower degrees of weathering (<51 % of total Fe), higher proportion of poorly crystalline Fe minerals (>0.15), lower א lf (<25 x10-8m3kg-1) and אfd (<2%), as well as greater average enhancements on heating of א lf (265% at 500C) and א fd (8.4 percentiles at 700C) than well-drained soils.

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