EFFECTIVENESS OF WATERSHED LAND-MANAGEMENT PRACTICES TO IMPROVE WATER QUALITY
Title: Sorbent-amended compost filter socks in grassed waterways reduce nutrient losses in surface runoff from corn fields
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 25, 2011
Publication Date: September 24, 2012
Citation: Shipitalo, M.J., Bonta, J.V., Owens, L.B. 2012. Sorbent-amended compost filter socks in grassed waterways reduce nutrient losses in surface runoff from corn fields. Journal of Soil and Water Conservation. 67(5):433-441.
Interpretive Summary: When rainfall occurs on cropped fields it can generate runoff that erodes the soil and transports some of the fertilizer and herbicide used to produce the crop into streams and lakes. The amount of sediment that is lost can be reduced by diverting the runoff into grassed waterways that slow water movement and trap some of the soil. Sediment losses can be further reduced by placing mesh tubes filled with compost in the waterways, which partially filter the water as it moves down the waterways. While the combination of compost filter socks and grassed waterways is not very effective in reducing the losses of dissolved fertilizer and herbicides, materials that help retain these substances can be added to the compost to help remove them from the runoff. In this study we investigated one such commercially available material and found that it helped reduce the concentration of dissolved phosphorus in the runoff. Phosphorus is a fertilizer nutrient that has been linked to degradation of surface water and algal blooms. Some of the material that was used to help retain the phosphorus, however, was leached from the filter socks, although not at levels that are of concern. Thus filter socks, used in conjunction with other conservation measures, can help reduce concentrations of sediment, herbicides, and nutrients in grassed waterways. Nevertheless, further research and development is needed to quantify the effectiveness of adding materials to filter socks to increase their ability to retain nutrients.
Surface runoff from fields used to grow row crops frequently has high concentrations of sediment, nutrients, and pesticides, particularly in the first few events after tillage and agrochemical application. Compost filter socks placed in grassed waterways can further reduce sediment concentration as runoff is transmitted offsite, but are generally ineffective in removing dissolved chemicals. Therefore, we investigated the effect of adding a proprietary sorbent, Nutriloxx, to filter socks filled with composted bark and wood chips on sediment, nutrient, and glyphosate concentrations in runoff. Surface runoff from one tilled and one no-till watershed planted to corn (Zea mays L.) was routed into two parallel, 30-m (99 ft) long, grassed waterways. Three, 46-cm (18 in) dia., filter socks with filled with Nutriloxx-amended compost were placed 5 m (16.5 ft) apart across the upper half of one waterway and in the lower half of the paired waterway. Automated samplers were used to obtain samples above and below the treated waterway segments in the 2009 and 2010 crop years. The effectiveness of the grassed waterways and filter socks was highly dependent on tillage treatment and timing and size of the runoff events. In 2009 there were no sizable events during the early growing season. Consequently, sediment loses were minimal and no significant effects on sediment concentration were detected. Averaged for both watersheds, however, the amended filter socks contributed to an additional 28% reduction in dissolved phosphorus concentration compared to waterway segments without filter socks (significant @ p = 0.05). The filter socks, however, significantly increased sulfate concentrations up to 20-fold in the first sampled event, but sulfate concentrations declined rapidly with subsequently events. Similarly, the filter socks increased concentrations of calcium, potassium, and sodium, but this was not significant in all instances. In 2010 runoff-producing rainfall occurred frequently during the growing season and the filter socks significantly decreased sediment and dissolved phosphorus concentrations from the tilled watershed. In addition, large reductions in ammonium nitrogen concentrations were noted (average > 7-fold), but field observations suggested that this was due to physical trapping of eroded coated-urea fertilizer prills rather than sorption. The filter socks continued to contribute to significantly increased sulfate concentrations from both watersheds. Filter socks can effectively reduce sediment losses when used in agricultural applications and adding selective sorbents can increase their ability to retain nutrients, but losses of sorbent components need to be considered.