| Summary: | The impact of the aeration status of soils on the environmental fate of the soil-applied pre-emergent herbicide metolachlor is of significance to sustainable agriculture practices and has not been investigated thoroughly by existing research works. To address this knowledge gap, we examined the adsorption, desorption, degradation, and mineralization of radioactively labeled [<sup>14</sup>C] metolachlor in Catlin, Flanagan, and Drummer soils under aerobic and anaerobic conditions. Based on our findings, anaerobic conditions in the soil significantly reduced the adsorption of <sup>14</sup>C-metolachlor while also promoting its desorption, thereby potentially releasing a greater amount of herbicide from the soil after a field application. The first-order degradation and mineralization kinetics of <sup>14</sup>C-metolachlor were distinctively enhanced by anaerobic conditions in all the soils tested. Furthermore, the degradation and mineralization rates of <sup>14</sup>C-metolachlor in non-sterilized versus sterilized soil microcosms clearly indicated microbial activity in the degradation of metolachlor in soil. The results from this study suggest that soil redox conditions could impact the bioavailability and environmental fate of herbicide metolachlor and should be taken into consideration as part of sustainable weed management programs.
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