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Stabilization of clay sized microaggregates in rhizosphere environment Mandal Debashis*, Datta S.C. Division of Soil Science and Agricultural Chemistry, IARI, New Delhi-110012. *Central Soil and Water Conservation Research & Training Institute, Dehradun, 248195, India; email:demichael@rediffmail.com.
Abstract Association of organic matter with minerals has often been recognized as one principal process leading to the stabilization of organic matter against degradation in soils and sediments. Stable structure is resulted from increased proportion of water stable organo-clay microaggregates and the organic matter trapped within microaggregates. Kinetics study of organo-mineral micro aggregates with respect to thermal stability is very important particularly in tropical and subtropical countries due to high decomposition pressure. Aggregate breakdown leads to detachment of particles, which favours superficial crusting, runoff and transport. In the present study, clay sized microaggregates were separated from rhizosphere of 90 days old soybean grown on 4 soils belonging to the order Alfisols and Vertisols. Clay-sized fractions of these aggregates were then isolated by fractionation method. Samples were kept at 35°C and 55°C for incubation study to observe rate of decomposition of organic matter. Organic carbon content was analyzed at frequent intervals of time which were found to decrease with time. Kinetic study showed that the best fit curve was a quadratic equation (Y = A+Bx+Cx2) with a larger negative B and a smaller positive C coefficients. Rate of decomposition was interpreted as a net result of two opposing processes -one a constant rate of decomposition and another a time dependent stability factor due to adsorption of organic molecules on clay. Differential X-ray Diffraction (DXRD) studies confirmed the finding that the complex formation took place in the interlayer region of smectite clay minerals particularly in the rhizosphere soils. The study also revealed that the susceptibility of microaggregates to breakdown into finer, more transportable particles was more in Alfisols than Vertisols. which in consequence forms rapid encrustation. Top Key words Clay sized microaggregates, Differential X-ray diffraction, Rhizosphere, Soybean, Thermal stability. Top | |
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