EFFECTIVENESS OF WATERSHED LAND-MANAGEMENT PRACTICES TO IMPROVE WATER QUALITY
Title: Impact of Grassed Waterways and Compost Filter Socks on the Quality of Surface Runoff from Corn Fields
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 2009
Publication Date: March 3, 2010
Citation: Shipitalo, M.J., Bonta, J.V., Dayton, E.A., Owens, L.B. 2010. Impact of grassed waterways and compost filter socks on the quality of surface runoff from corn fields. Journal of Environmental Quality 39(3):1009-1018.
Interpretive Summary: The water that runs off crop fields can contain large amounts of eroded soil as well as some of the fertilizer and herbicide used to produce the crop. Conservation tillage practices, which entail leaving some of the residue from the previous crop on the ground, can help to reduce the amount of sediment lost in the runoff, but do little to reduce losses of nutrients and herbicides that are dissolved in the water. Grassed waterways can further reduce the sediment content of the runoff before it reaches permanent bodies of water, but are also generally ineffective in removing dissolved crop production chemicals.
In this two-year field study we investigated whether placing mesh tubes filled with compost across the grassed waterways can further improve the quality of runoff. These devices are referred to as filter socks and are approved for usage at construction sites for runoff control as an alternative to silt fences and bales of straw, but have not been tested in agricultural fields. Our results indicated that the filter socks can significantly reduce concentrations of sediment and some herbicides, but were not effective in removing fertilizer nutrients. Continuing investigations in which different materials are added to the compost to improve the removal of nutrients and herbicides are being conducted. If these experiments are successful, filter socks may become another tool that can be used by farmers and conservationists to reduce the impact of crop production on surface water quality.
Surface runoff from cropland frequently has high concentrations of nutrients and herbicides, particularly in the first few events after application. Grassed waterways can control erosion while transmitting this runoff offsite, but are generally ineffective in removing dissolved agrochemicals. In this study, we routed runoff from one tilled (0.7 ha) and one no-till watershed (0.8 ha) planted to corn into parallel, 30-m long, grassed waterways. Two, 46-cm dia., filter socks filled with composted bark and wood chips were placed 7.5 m apart in the upper half of one waterway and in the lower half 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 filter socks had no significant effect (P = 0.05) on sediment concentrations for runoff from the no-till watershed, but contributed to an additional 49% reduction in average sediment concentration compared to unamended waterways used with the tilled watershed. The filter socks significantly increased the concentrations of Cl, NO3-N, PO4-P, SO4, Ca, K, Na, and Mg in runoff from at least one watershed, however, probably due to soluble forms of these ions in the compost. The estimated additional amounts contributed by the socks each year ranged from 0.04 to 1.25 kg, thus were likely to be inconsequential. The filter socks contributed to a significant additional reduction in glyphosate (5%) and alachlor (18%) concentrations for the tilled watersheds, but this was insufficient to reduce alachlor concentrations to acceptable levels.