Herbicide Losses From Terraced Tile Inlet Technologies

ABSTRACT Terraced agricultural fields in the Midwestern United States commonly use surface inlets to mitigate ponding and enhance drainage; however, these structures can also facilitate herbicide transport to downstream waters. This study evaluated four terraced tile inlet technologies: Hickenbottom riser (HBR), water quality inlet (WQI), blind inlet (BI) and HBR with channel laterals (HBR + CL) for their effectiveness in reducing herbicide losses in run‐off. Four run‐off events were monitored during the 2024 soybean season and four during the 2025 corn season. Herbicides analysed included atrazine, chlorimuron‐ethyl, dimethenamid ‐P , fluthiacet‐methyl, glyphosate, mesotrione, pyroxasulfone, metolachlor, saflufenacil and sulfentrazone. In 2024, chlorimuron‐ethyl and fluthiacet‐methyl concentrations remained below detection limits (< 0.10 μg L −1 ) across all events. Following post‐emergence applications, glyphosate concentrations were higher for WQI (3.21 μg L −1 ) than for HBR and BI (0.77–0.96 μg L −1 ); however, no significant differences in median herbicide loads were observed among inlet types. In 2025, residual glyphosate was detected before application, with concentrations ranging from 0.25 (BI) to 1.46 μg L −1 (HBR). Atrazine concentrations exceeded the USEPA‐MCL (3 μg L −1 ) during one event, but seasonal median concentrations were below MCL when all herbicides were applied without a setback from the inlet. The BI had 61% lower median saflufenacil concentrations, while both BI and WQI had 43% lower dimethenamid ‐P concentrations compared to other inlets. Across all events in 2025, glyphosate concentrations were highest for HBR, whereas BI consistently resulted in the lowest herbicide loads, primarily due to reduced discharge. These results indicate that incorporating filtering materials, such as calcium carbonate aggregates, into BI can effectively reduce herbicide transport and improve run‐off water quality.