A NATURALLY-OCCURRING CLAY-ORGANIC COMPLEX IN SOME SOILS IN INDIA

The <2 mu m fraction of a clay-organic complex (COG) ultrasonically se parated from the four surface soil samples and treated to remove organ ic matter (OM) and OM plus iron and aluminium oxides. As expected, COC was characterised by higher CEC, total Ca and Mg content than the tre ated complex. A part of total Ca bridges between OM and clay and exist possibly in exchangeable form so as to serve as an easily available n utrient reservoir, while highly insoluble Ca minerals like apatites ca rbonates and feldspars could form the other part. The portion of OM ea sily oxidisable by H2O2 seems to be associated with Ca and Mg by its c arboxylic groups while the residual OM remains in association with Fe, Al oxides.