Nitrogen export from Coastal Plain field ditches

Mitigating the adverse impact of nitrogen (N) fertilizer applications depends on an understanding of transport mechanisms and flow pathways. The objective of this study was to quantify N export from seven ditches on the Maryland Eastern Shore. Ditches were monitored between June 2005 and May 2006, including flow and sample analyses for storms and base flow. Mean total N and NO₃-N concentrations were 10.6 and 6.0 mg L^-1 (10.6 and 6.0 ppm) for ditch 8, which were 2 times the total N and NO₃-N concentrations for any other ditch. Greater mean concentrations in ditch 8 translated to 43.5 kg ha^-1 (38.8 lb ac^-1) total N loss and 24.9 kg ha^-1 (22.2 lb ac^-1) NO₃-N loss, which were not consistent with losses observed for any of the other ditches. The elevated losses in ditch 8 coincided with the presence of a manure storage shed located in this drainage basin. The two ditches (7 and 8) nearest the manure storage shed had the greatest increase in organic N loss as a function of drainage outflow, increasing 0.062 kg ha^-1 (1.56 lb ac^-1) per mm (in) drainage outflow compared to 0.017 kg ha^-1 (0.45 lb ac^-1) per mm (in) outflow for the other five ditches. Ditches 2 and 3 had the greatest outflow of water (640 mm [25.2 in]), contributing to greater NO₃-N loads - a consequence of greater groundwater drainage. Implementing management strategies that mitigate N losses from agricultural fields should be considered in the context of ditch hydrology and drainage basin features.