Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/20/2007
Publication Date: 8/1/2007
Citation: Kroger, R., Holland, M.M., Moore, M.T., Cooper, C.M. 2007. Hydrological variability and agricultural drainage ditch nutrient mitigation capacity: Inorganic nitrogen. Journal of Environmental Quality. 36:1646-1652. Interpretive Summary: Drainage from agricultural lands may contain excess nutrients in some regions of the U.S. Farm ditches were sampled for two years for baseflow and stormflow nitrogen concentrations. The vegetated drainage ditches reduced the load of dissolved inorganic nitrogen leaving the fields 57% over two years. Information on how nutrients are transported from fields through ditches will aid farmers and other conservationists in adequately designing strategies to mitigate potential downstream effects of excessive nutrient runoff.
Technical Abstract: The application of inorganic nitrogen fertilizers on agricultural landscapes has the potential to generate environmental degradation concerns at fine to coarse scales across the catchment and landscape. Inorganic nitrogen species (nitrate, nitrite, ammonia) are typically associated with subsurface flow processes and react differently hydrologically than phosphorus species. Nitrogen mitigation capacity of agricultural drainage ditches under no-till cotton was determined under natural, variable rainfall conditions in north Mississippi. Storm generated overland runoff and stormflows were sampled at equidistant stratified sampling sites within two experimental farm ditches for two years. Inorganic nitrogen concentrations, in conjunction with Manning’s equation and NRCS dimensionless hydrographs, provided total water volumes per storm event, and maximum effluent and outflow nitrogen loads. Both baseflow and storm regression results indicated the drainage ditches to be sinks to nitrate and ammonia over both growing and dormant seasons. Overall maximum storm loads of dissolved inorganic nitrogen (DIN) from the farm over the two year sampling period accounted for 6.8% of the initial fertilizer application, of which 3% actually left the ditch (0.84 kg/ha/yr): a 57% ditch reduction of DIN load over two years. Watershed based long-term sampling incorporating nutrient load outflow, hydrological and farming management data will provide critical information on inorganic N losses as influenced by hydrology and best management practices.