Clay-organic complexation and mineral transformation in the rhizosphere during cropping: A study through Differential X-ray Diffraction (DXRD) and fitting of XRD profile Mandal Debashish1, Datta S.C. Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi, 110 012 1Present address: Central Soil and Water Conservation Research & Training Institute, Dehradun, 248 195 Abstract This study was attempted to investigate the effect of rhizosphere which is a site of intense microbial activity on clay-organic complexation and mineral transformation. Clayorganic complexes were dispersed from surface sample of four different soils belonging to the order Alfisols and Vertisols by ultra sonification after growing successively wheat and soybean crops in pots containing one kg soil. The clay-size fraction of these clay-organic complexes were isolated by fractionation method and termed as rhizosphere sample. Nonrhizosphere samples were collected from similar sets of pots kept without crops. Preferred oriented Mg-saturated samples of both rhizosphere and non-rhizosphere were scanned for X-ray diffraction before and after treatment with 30 per cent H2O2 to remove organic matter. Fitting of XRD profile showed that in the rhizosphere sample organic molecules haveentered the interlayer space and increased the basal spacing to 28 Å. A portion of smectite has also been to be transformed to randomly interstratified smectite-kaolinite minerals. Differential X-ray diffraction obtained by subtracting digital X-ray scanned data of H2O2 treated sample from untreated sample after multiplying with a correction factor showed that clay-organic complex formed in the rhizosphere sample of Vertisol were seemed to be more stable than that of Alfisol. Top |