Ashes produced during on-farm burning of crop residues are mixed in soil before sowing next crop and studies suggest that they can enhance adsorption of pesticides in soil. Enhanced adsorption of pesticides in soil can reduce their availability for degradation and pest/weed control. Therefore, present study evaluated effect of sugarcane trash ash (STA) on degradation of atrazine (used to control annual grasses and many broad-leaved weeds) and fipronil (used for control of early shoot borer and termites) in three sugarcane growing soils and bioavailability of atrazine. Three sugarcane-growing soils (silty clay loam, sandy clay loam and loam) were used to study effect of 0.1 and 0.2\% STA on atrazine and fipronil degradation in laboratory incubated soils. Field study for effect of STA on atrazine degradation was performed in silty clay loam soil. Effect of STA on atrazine bioavailability was assayed using its effect on mustard seed germination. Pesticides and their metabolites were quantified using high-performance liquid chromatography (HPLC)/ gas-liquid chromatography (GLC)/ liquid chromatography-mass spectroscopy (LC-MS/MS). Under laboratory condition 0.2\% STA doubled atrazine half-life (t(1/2)) in sandy clay loam, increased t(1/2) by 40\% in silty clay loam, while no significant effect was observed in loam soil. The STA did not affect fipronil degradation in all three soils. Metabolites, hydroxyatrazine and deethylatrazine (atrazine) and sulfide, sulfone, amide and desulfinyl (fipronil) were detected in soil samples; but their spectrum and quantities varied with the soil type. The t(1/2) of atrazine under field condition was 3.61, 2.73 and 2.86 days in control, 0.1\% and 0.2\% STA-mixed silty clay loam, respectively. The STA reduced atrazine availability suggesting that higher amount of herbicide will be needs for the desired effect in STA-mixed soils. This study has relevance in assessing fate and bioavailability of atrazine and fipronil in sugarcane soils where trash is burnt year after year and mixed in soils. The STA mixing might have cumulative effect due to regular burning of trash.