Variability of Soils in Two Rice Growing Toposequences

In the Brahmaputra valley, two typical rice growing areas with topographical variations, one in north (North Lakhimpur) and another in south bank (Shillongani) of the Brahmaputra river were selected and from each site three pedons representing different topographic positions were studied. In both the toposequences, soils in lower position were heavier in texture, and higher in organic matter, free sesquioxides, exchangeable cations, CEC and base saturation than the soils in upland situation. Surface soils of all the pedons were more fertile and there was a fertility gradient with increasing fertility status down the slope. The soils were classified as Aeric Epiaquepts (upland), Aeric Endoaquepts (midland) and Typic Endoaquepts (lowland). Climate was the dominant factor for variation in soil properties between the toposequences. In each toposequence, microrelief played an important role in soil formation.