Author(s):

Pallabi Kalita, Marami Dutta, RM Karmakar, S Dutta and B Deka

Abstract: Iron and aluminium are the two most essential elements for understanding various soil forming processes. Profile distribution of different forms of Fe and Al oxides, particularly dithionite and oxalate extractable Fe and Al, serves as useful indicators to identify the horizon for accumulation of secondary oxides and the depth of argillic horizon. The investigation was carried out in Golaghat district of Assam taking five soil profiles from different land uses viz., forest, paddy, tea, bamboo and vegetable. Different extractants were used to determine various forms of Fe and Al viz., CBD, ammonium oxalate and sodium pyrophosphate. It was found that among the pedogenic iron and aluminium oxides, dithionite extractable iron (Fe_d) and aluminium (Al_d) content was highest in all the pedons irrespective of land uses. On the weighted mean basis, paddy soil recorded the highest Fe_d and Al_d. The depth distribution was irregular for oxalate extractable iron (Fe_o) and aluminium (Al_o), amorphous inorganic iron (Fe_o – Fe_p) and aluminium (Al_o – Al_p) and crystalline form of aluminium (Al_d – Al_o) within a profile. On the weighted mean basis, vegetable soil recorded highest Fe_o, paddy soil recorded highest (Fe_o – Fe_p) and forest soil recorded the highest (Fe_d – Fe_o). Also bamboo soil recorded the highest Al_o and (Al_o – Al_p) and forest soil recorded highest (Al_d – Al_o). The surface horizons recorded comparatively higher amount of Fe_p and Al_p than the subsurface horizons in all the pedons. The activation ratios, Fe_o/Fe_d and Al_o/Al_d were highest for vegetable soil and bamboo soils respectively, which indicates that these two are relatively young soil. The increasing trend of clay/Fe_d and clay/Al_d ratios within a profile in forest, paddy and tea soils is indicative that these are relatively weathered soils. These ratios follows inconsistent trend in bamboo and vegetable soils. Correlation studies among different forms of Fe and Al and selected soil properties were also examined.

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