Characterization of Fe-Mn Glaebules in some Alluvial Derived Soils of Assam under Paddy and Non-paddy Land Use

Iron-manganese glaebules from paddy and non-paddy alluvial soils of Assam were studied for their morphological, chemical and mineralogical characteristics as well as genesis. Both size and content of glaebules increased with increase in depth of soils. Hard glaebules were associated with poorly drained soils. The colour of glaebules ranged from yellowish brown to dark yellowish brown. The size of the glaebules were larger in well drained ponded paddy soils as compared to that of non-paddy soils. The reverse was true for naturally poorly drained paddy soils. The content of Fe, Mn, P and in some cases Cu were higher and that of Si, Na, K, Mn and in some cases Ca were lower in glaebules than soil matrix. Glaebules from paddy soils had higher content of Fe, Mn, P and Cu than that of non-paddy soils. Manganese enrichment was higher in glaebules from paddy than the non-paddy soils. Both Mn and P increased with increase in size of glaebules. Copper and P were significantly correlated with Fe and Mn, respectively. Quartz, mica, feldspars, kaolinite, goethite and meghemite were invariably present in all glaebules. Hematite was either absent or low in glaebules from paddy soils as compared to that of non-paddy soils. The content of Si as well as quartz decreased with progress in glaebules development. The glaebules were formed in situ through reducto-eluviation and precipitation of Fe and Mn under alternate wetting and dryin,g cycle.