NITROGEN EXPORT FROM COASTAL PLAIN FIELD DITCHES

Authors: Schmidt, John; Dell, Curtis; Vadas, Peter; ALLEN, ARTHUR - UMES

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2007
Publication Date: 7/1/2007
Citation: Schmidt, J.P., Dell, C.J., Vadas, P.A., Allen, A.L. 2007. Nitrogen export from coastal plain field ditches. Journal of Soil and Water Conservation. 62(4):235-243.

Interpretive Summary: Successfully mitigating the adverse impact of agricultural N and P applications will depend on a sound understanding of transport mechanisms and flow pathways (from fields). The objective of this study was to evaluate N losses from ditches for a Coastal Plain landscape on the Maryland Eastern Shore, considering implications for management practices that potentially mitigate N losses from agricultural fields. Mean total- and nitrate-N concentrations were 10.6 and 6.0 mg per L for Ditch 8, which were more than twice as much than any of the other six ditches evaluated in this study. Greater concentrations in Ditch 8 outflow translated to 38.8 lb per acre total N losses and 22.2 lb per acre nitrate N in annual losses, which were almost 3X more than losses observed for any other ditches. The elevated losses in Ditch 8 coincided with the presence of poultry barns and a manure storage shed (point sources) located in this drainage basin. The three ditches nearest the poultry barns also had the greatest increase in organic N loss as a function of drainage outflow, increasing 1.56 lb per acre per inch drainage outflow compared to 0.45 lb per acre per inch outflow for the four other ditches. Ditches 2 and 3 had the greatest annual outflow of water (more than 353,000 cubic ft), which contributed to greater nitrate-N loads and could be attributed to greater groundwater drainage. While controlled drainage, riparian areas, or biological curtains might successfully mitigate N losses from Ditches 2 and 3, these practices would be ineffective for the shallower ditches. A vegetative grass strip could be used to effectively decrease N losses in the surface runoff of the latter ditches. Implementing management strategies that mitigate N losses from agricultural fields should be considered in the context of ditch and drainage basin features.

Technical Abstract: Successfully mitigating the adverse impact of agricultural N and P applications will depend on a sound understanding of transport mechanisms and flow pathways (from fields). The objective of this study was to evaluate N losses from ditches for a Coastal Plain landscape on the Maryland Eastern Shore, considering implications for management practices that potentially mitigate N losses from agricultural fields. Seven ditches on the University of Maryland – Eastern Shore’s Research Farm were monitored between May 2005 and June 2006, including flow and sample analyses for storms and base flow. Total N and nitrate N were determined for all samples. An annual flow-weighted mean concentration was determined by summing monthly load and then dividing by total flow. Mean total- and nitrate-N concentrations were 10.6 and 6.0 mg per L for Ditch 8, which were, respectively, 5.1 and 3.4 mg per L more than total-N and nitrate-N concentrations for any other ditch. Greater mean concentrations in Ditch 8 outflow translated to 38.8 lb per acre total N losses and 22.2 lb per acre nitrate N in annual losses, which were, respectively, 13.0 and 6.6 lb per acre more than losses observed for any other ditches. The elevated losses in Ditch 8 coincided with the presence of poultry barns and a manure storage shed (point sources) located in this drainage basin. The three ditches nearest the poultry barns also had the greatest increase in organic N loss as a function of drainage outflow, increasing 1.56 lb per acre per inch drainage outflow compared to 0.45 lb per acre per inch outflow for the four other ditches. Ditches 2 and 3 had the greatest annual outflow of water (more than 353,000 cubic ft), which contributed to greater nitrate-N loads and could be attributed to greater groundwater drainage. While controlled drainage, riparian areas, or biological curtains might successfully mitigate N losses from Ditches 2 and 3, these practices would be ineffective for the shallower ditches. A vegetative grass strip could be used to effectively decrease N losses in the surface runoff of the latter ditches. Implementing management strategies that mitigate N losses from agricultural fields should be considered in the context of ditch and drainage basin features.