Crop residue ashes reduce leaching, persistence and bioavailability of sulfosulfuron and pretilachlor used in the succeeding crop

Ash produced during burning of crop biomass may affect the behaviour of herbicides applied in the crops sown after burning. Therefore, the effect of wheat straw ash (WSA) on pretilachlor and rice straw ash (RSA) on sulfosulfuron leaching, degradation and bioactivity in soils was studied. Both ash types reduced downward mobility of respective herbicides, but the effect varied with soil type and dose of ash. Effect was greater in the sandy loam soil because masking of ash was observed in the clay loam soil. Pretilachlor degradation studies indicated that the WSA enhanced degradation and effect was greater in the flooded soil where 0.2% ash reduced the half-life (t(1/2)) by nearly half, whereas increasing the ash content to 0.5% slightly increased the t(1/2) values. The effect of RSA on sulfosulfuron degradation was significant in the sandy loam soil. A pot culture study in wheat also confirmed these results. The effect of the WSA on the bioavailability of sulfosulfuron was assayed by observing its effect on mustard seedlings and results suggested that even 0.1% WSA reduced herbicide availability. Burning of crop residues on field is a major concern due to air pollution, but also affects the fate of soil-applied herbicides. Our study has implications in assaying the role of crop ashes on pesticide fate in soils where crop residues are burned regularly.