Leaching behaviour of atrazine and fipronil in sugarcane trash ash mixed soils

Crop residue ashes exhibit significant capacity to adsorb pesticides and affect their adsorption behaviour in soils. The present study evaluated the effect of sugarcane trash ash (STA), the third most important crop whose residues are burnt in fields in India, on atrazine and fipronil leaching behaviour in three sugarcane growing soils. The STA reduced downward mobility of atrazine in soils but, effect varied with the soil type. No atrazine residues were detected in the leachate. Atrazine was fairly mobile in the sandy loam soil than the loam and the clay loam soils and increasing leaching intensity from 64 to 128 mm, further increased herbicide’s downward mobility. Significant atrazine degradation was observed during leaching process and 38–43, 1.5–12.5 and 27–41% of column applied atrazine was degraded in the silty clay loam, the sandy clay loam and the loam soils, respectively. Higher atrazine degradation in the clay loam and the loam soils was attributed to slow water percolation rate and longer time to complete leaching process. Hydroxyatrazine, deethylatrazine and deisopropylatrazine metabolites of atrazine were detected in the soil samples, but their amounts varied in different treatments. Compared to atrazine, fipronil was highly retained in the surface layer (0–5 cm) in the control and STA-mixed soil columns and no fipronil was detected in the leachate. Trash burning is a regular practice; therefore, continuous mixing of STA in soils can reduce leaching of mobile pesticides applied in sugarcane crop. This study has implications in identifying the role of crop residue burning on fate of pesticides applied in soils.