Laboratory  equilibration studies were undertaken to evaluate the effect of solid wastes application individually or in co-application on Q/I relationship and soil properties.  Amending the soil, with fly ash/ sewage sludge with or without 50 ppm K increased the equilibrium activity ratio (AReK) values, decreased the labile pool (- KO) K and Gibb's free energy (- DG) values in vertisols. Whereas, potential buffering capacity (PBCK) values decreased.  Prolonged equilibration of soils for 50 days decreased the AReK values, - DKo values and PBCk values.  Application of fly ash and sewage sludge as soil amendment increased the immediate availability of potassium, labile pool and PBCk to a greater extent in vertisols.