Monday, November 2, 2009
Convention Center, Exhibit Hall BC, Second Floor
Surface runoff from fields used to grow row crops frequently has high concentrations of nutrients and herbicides, particularly in the first few events after application of these materials. Grassed waterways can be used to transmit this runoff to streams and can help control erosion, but are generally ineffective in removing dissolved agrochemicals. In this study, we routed the runoff from one tilled and one no-till watershed (~1.0 ha) planted to corn into parallel, 30 m long, grassed waterways designed by the NRCS. Two, 46-cm dia., mesh bags (filter socks) filled with composted bark and wood chips were placed 7.5 m apart across the upper half of one waterway and two socks were similarly placed in the lower portion of the other waterway to determine if they increased removal of sediment and dissolved chemicals. Automated samplers were used to obtain samples above and below the treated segments of the waterways for two crop years. The effectiveness of the grassed waterways and filter socks was highly dependent on the timing and size of the runoff events and tillage treatment. Averaged for both years and watersheds, sediment concentration increased by 18% compared to the input concentration due to erosion within the waterways in some high flow rate events, but a 33% overall reduction in sediment concentration was noted when filter socks were added to the waterways. Atrazine concentrations were reduced by 19% and 25% in the grassed waterways and waterways with filter socks, respectively. For glyphosate these reductions were 22% and 24%. The filter socks also had a negligible effect on dissolved P and nitrate-N concentrations. With the configuration investigated, compost-filled filter socks improved the performance of grassed waterways by reducing sediment concentrations, but only had a minimal effect on dissolved nutrients and herbicides.