Abstract
Distribution of different forms of Fe in two red soils (Kotwalipur and Anusuya series) and one alluvial soil (Satna series) in Madhya Pradesh, India, were studied by a selective extraction procedure with 10 extractants, viz., KCI, NH4OAc, HCI, Diethylenetriamine-pentaacetic acid (DTPA), Cyclohexanediamine-tetraacetic acid (CDTA), acetic acid, Ethylenediamine-tetraacetic acid (EDTA), pyrophosphate, oxalate, and dithionite. Relative extractability of the extractants was : Dithionite > oxalate > pyrophosphate > EDTA > acetic acid > HCI > CDTA > KCI > DTPA > ammonium acetate. The soil series can be arranged on the basis of mean values of Fe extracted by KCI, ammonium acetate, HCI, and pyrophosphate as Kotwalipur > Satna > Anusuya; DTPA, acetic acid, and oxalate as Satna > Kotwalipur > Anusuya and CDTA, EDTA, and dithionite as Kotwalipur > Anusuya > Satna. Moreover, analyses of pyrophosphate, oxalate, and dithionite extractable Fe showed that with increasing soil age, the crystalline iron oxides increase at the expense of the poorly crystalline forms. This trend is reflected in the ratio of Feo :Fedi (Feratio). The mean contents of amorphous Fe and the Fe :Fed ratio values estimated the degree of soil development and were found to be in the following descending order: Anusuya > Kotwalipur > Satna. Correlation between different forms of Fe and selected soil properties were examined.
