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This article in JEQ

  1. Vol. 26 No. 4, p. 1038-1048
    Received: Oct 21, 1996

    * Corresponding author(s): m-david@uiuc.edu


Nitrogen Balance in and Export from an Agricultural Watershed

  1. Mark B. David *,
  2. Lowell E. Gentry,
  3. David A. Kovacic and
  4. Karen M. Smith
  1. University of Illinois, Department of Natural Resources and Environmental Sciences, W-503 Turner Hall, 1102 South Goodwin Av., Urbana, IL 61801;
    University of Illinois, Department of Landscape Architecture, 101 Temple Buell Hall, 611 East Lorado Taft Drive, Champaign, IL 61820.



Surface water nitrate (NO3) pollution from agricultural production is well established, although few studies have linked field N budgets, NO3 loss in tile drained watersheds, and surface water NO3 loads. This study was conducted to determine field sources, transport, and river export of NO3 from an agricultural watershed. The Embarras River watershed at Camargo (48 173 ha) in east-central Illinois was investigated. The watershed is a tile-drained area of fertile Mollisols (typical soil is Drummer silty clay loam, a fine-silty, mixed mesic Typic Haplaquoll) with primary cropping of maize (Zea mays L.) and soybean (Glycine max L.). Agricultural field N sources and sinks, tile drainage NO3 concentrations and fluxes, and river NO3 export were estimated for the entire watershed. Large pools of inorganic N were present following each harvest of maize and soybean (average of 3670 Mg N yr−1 over a 6-yr period). The source of most of the inorganic N was divided between N fertilizer and soil mineralized N. High concentrations of NO3 were found in four monitored drainage tiles (5–49 mg N L−1), and tile concentrations of NO3 were synchronous with Embarras River NO3 concentrations. High flow events contributed most of the yearly NO3 loss (24.7 kg N ha−1 yr−1) from tile drained fields in the 1995 water year (1 Oct. 1994 through 30 Sept. 1995) where high rainfall events occurred in a low overall precipitation year (in one tile 21% of the annual load was exported in 1 d). During the 1996 water year, NO3 export in tiles was much higher (44.2 kg N ha−1 yr−1) due to greater precipitation, and individual days were less important. On average, about 49% (average of 1688 Mg N yr−1 over a 6-yr period) of the field inorganic N pool was estimated to be leached through drain tiles and seepage and was exported by the Embarras River, although depending on weather and field N balances this ranged from 25 to 85% of the field N balance over the 6-yr period. It seems likely that agricultural disturbance (high mineralization inputs of N) and N fertilization combined with tile drainage contributed significantly to NO3 export in the Embarras River.

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