Biochar-Amended Filter Socks Reduce Herbicide Losses Via Tile Line Surface Inlets.

Standing water in depressions and behind terraces in fields with subsurface drainage systems can result in reduced crop yields. This concern can be partially alleviated by installing surface inlets that reduce the duration of ponding. Unfortunately, these inlets provide an open conduit for surface water to enter subsurface drains, thus can contribute to water quality concerns. Encircling surface inlets with woodchip-filled filter socks has been shown to reduce sediment and nutrient concentrations, but herbicide losses may also be a concern. Therefore, we investigated whether adding biochar to filter socks can increase their ability to sorb herbicides. Three surface inlets behind terraces in a single corn (Zea mays L.) field were used in this study. Each of the three inlets was replaced with two identical inlets ~ 5 m apart at the same elevation resulting in three pairs of twinned inlets. Woodchip-filled filter socks were placed around one inlet and socks filled with a 50:50 mixture (by volume) of woodchips and hardwood-derived biochar were placed around the other inlet in each pair. When ponding occurred ISCO samplers were used to simultaneously withdraw samples from each inlet every 30 min after it passed through the filter socks. The samples were analyzed for atrazine, isoxaflutole, thiencarbazone-methyl, sediment, and nutrient concentrations. Due limited rainfall, there were few, small, runoff events during the 2017 growing season. Both sock types reduced sediment and total P concentrations by ~ 1/2, but had little effect on dissolved P. Similar reductions in atrazine concentrations of ~ 1/3 were noted for both sock types, while no trends were evident for the other herbicides.