Abstract Delaying cover crop termination until planting (i.e., planting green) in no-till production systems is likely to mediate the fate of herbicides that provide soil residual activity. In a planting green scenario, there is currently limited knowledge of how the interaction between physiochemical properties of cover crop residues and sorption properties of herbicides influence the washoff potential of residual herbicides from cover crop residues. We conducted field- and laboratory-based experiments using herbicide washoff assay methods to evaluate the interaction between lignin (%) of cereal rye ( Secale cereale , L.) and herbicide lipophilicity (K ow ) on washoff potential across herbicide application timings. We contrasted herbicides with intermediate lipophilicity (atrazine, pyroxasulfone , and S -metolachlor) to less (mesotrione) and highly lipophilic (pendimethalin) herbicides. When applied into living cereal rye, washoff of atrazine and pyroxasulfone were greater than mesotrione and S -metolachlor. Pendimethalin had the least washoff potential. When applied into fresh- to aged-cereal rye residues (0 to 84 days after termination), pendimethalin washoff was below the detection threshold. Washoff of mesotrione, pyroxasulfone, and atrazine declined as lignin (%) in cereal rye residues increased, whereas a positive relationship between S -metolachlor recovery and lignin (%) was observed. Results of our study partially support the hypotheses that (1) herbicide lipophilicity, measured via log K ow values, can be a useful indicator of washoff potential among residual herbicides used in cover crop systems, and (2) washoff potential declines as cover crop residues age within herbicide application windows.
Smith et al. (Fri,) studied this question.