Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2007
Publication Date: 5/25/2007
Citation: Vaughan, R.E., Needelman, B.A., Kleinman, P.J., Allen, A.L. 2007. Spatial Variation of Soil Phosphorus Within a Drainage Ditch Network. Journal of Environmental Quality. 36(4):1096-1104. Interpretive Summary: Drainage ditches serve as important links between agricultural lands and surface waters, and have the potential to serve as key conduits of agricultural nutrients. This study examined the spatial distribution of phosphorus in a network of ditches found on the Eastern Shore of Maryland. Phosphorus and compounds that bound phosphorus were highly variable in drainage ditches. The highest concentrations of phosphorus were found in ditches draining barn areas, indicating a need to target remedial management to point source areas on farms. Results of the study will support the improved management of ditches for water quality protections.
Technical Abstract: Agricultural drainage ditches serve as P transport pathways from fields to surface waters. Little is known about the spatial variation of P at the soil-water interface within ditch networks. We quantified the spatial variation of surficial (0–5 cm) soil P within vegetated agricultural ditches on a farm in Princess Anne, Maryland with an approximately 30-yr history of poultry litter application. Ditch soils from 10 ditches were sampled at 10-m intervals and analyzed for acid ammonium oxalate-extractable P, Fe, Al, and pH. These variables were spatially autocorrelated. Oxalate-P (min = 135 mg/kg, max = 6919 mg kg-1, mean = 700 mg/kg) exhibited a high standard deviation across the study area (overall 580 mg/kg) and within individual ditches (maximum 1383 mg/kg). Several ditches contained distinct areas of high oxalate P, which were associated with either point- or non-point P sources. Oxalate-P was correlated with oxalate-Al or oxalate-Fe within specific ditches, although oxalate-Fe was not as well correlated with oxalate P across all ditches as was oxalate-Al. The high level of spatial variation of soil P observed in this ditch network suggests that spatially distributed sampling may be necessary in order to target best management practices and to model P transport and fate in ditch networks.