Elemental Composition and Association in Some Inceptisols and Alfisols of Assam under Varying Land Use

Paddy and associated non-paddy soils developed on alluvium of Brahmaputra and Barak valleys of Assam belonging to both Inceptisols and Alfisols, were investigated for total elemental composition and associations. Silicon was most abundant element followed by Fe, K, Na, Ca, Mg and P. Among trace elements Mn was most abundant followed by Zn and Cu. The relative abundance of Na, K, Ca, and Mg however, varied with degree of weathering of soils. The order of mobility of cations in soils under study was Ca> Na> Mg> K. In non-calcareous locations, paddy soils were enriched with Na and Ca, but depleted of Zn, whereas, in calcareous location, paddy soils were depleted of both Na and Ca as compared with associated non-paddy soils. Mobility of Fe and Mn was higher in paddy soils resulting in their redistribution in lower horizons. Long-term paddy cultivation (>80 years) resulted in depletion of both Fe and Mn, the depletion of Mn being greater than Fe. Paddy soils commonly showed increase in contents of Ca, Mg and Cu with depth. Depth distribution of P, Mn and Zn was irregular in all soils irrespective of land use. Differences in elemental association in respect of Si with Na and Ca, Ca with Mg, and Mn with Cu were noted between paddy and non-paddy soils. Organic carbon was not significantly correlated with any element under study.