Author(s):

Shraddha Mohanty and RM Karmakar

Abstract: Eight soil profiles collected from paddy and associated non-paddy soils of Jorhat (P1, NP1), Golaghat (P2, NP2), Sivsagar (P3, NP3) and Dibrugarh (P4, NP4) districts of Assam were studied for different forms of iron (Fe) viz., total (Fe_t), dithionite extractable (Fe_d), pyrophosphate extractable (Fe_p) and oxalate extractable (Fe_o) in the clay fraction using standard procedures. Total (Fe_t), dithionite extractable (Fe_d) and pyrophosphate extractable iron (Fe_p) in the clay fraction were slightly higher in non-paddy soils as compared to paddy soils whereas oxalate extractable iron (Fe_o) showed a reverse trend. Dithionite extractable iron (Fe_d) formed major portion of total iron content in the clay fraction followed by Fe_o and Fe_p in both paddy and non-paddy soils. Crystalline iron oxide (Fe_d-Fe_o) and silicate iron (Fe_t-Fe_d) was found to be higher in non-paddy soils while amorphous inorganic form of iron (Fe_o-Fe_p) showed the reverse trend. Different forms of Fe in the clay fraction were higher in illuvial B horizons due to presence of higher amount of clay. The Fe_d/Fe_t ratio was found to be higher in non-paddy soils than that of paddy soils. The active iron ratio (Fe_o/Fe_d) was higher in the surface horizon as compared to other horizons of a profile. Different fractions of soil organic carbon and the clay content had strong influence on the distribution of forms of Fe in the clay fraction of soil.

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