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Journal of Environmental Quality Abstract -

Organic Nitrogen in Drainage Water from Grassland in Northern Ireland


This article in JEQ

  1. Vol. 29 No. 4, p. 1233-1238
    Received: Oct 27, 1998

    * Corresponding author(s): c.watson@qub.ac.uk
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  1. C. J. Watson *,
  2. C. Jordan,
  3. S. D. Lennox,
  4. R. V. Smith and
  5. R. W. J. Steen
  1. Agricultural & Environmental Science Division, Dep. of Agriculture for Northern Ireland, Newforge Lane, Belfast, BT9 5PX, Northern Ireland;
    Biometrics Division; Dep. of Agriculture for Northern Ireland, Newforge Lane, Belfast, BT9 5PX, Northern Ireland.
    Agricultural Research Institute of Northern Ireland, Large Park, Hillsborough, County Down, BT26 6DR.
    Dep. of Agricultural and Environmental Science, The Queen's Univ. of Belfast.



Loss of organic N in land drainage may contribute to water pollution. This study was conducted to quantify the loss of organic nitrogen in drainage water from grazed grassland (Lolium perenne L. cv. Talbot) swards receiving a range of fertilizer N inputs for 9 yr. Plots (each 0.2 ha) received 100, 200, 300, 400, or 500 kg N ha−1 yr−1 as calcium ammonium nitrate and were hydrologically isolated and drained to V-notch weirs with automatic sampling of drainage water. For comparison, organic N loss was quantified in rivers draining six predominantly grassland catchments. The European Community maximum admissible concentration of total Kjeldahl N for drinking water of 1.0 mg N L−1 was exceeded in both land drainage and river water. Total organic N accounted for up to 54.7 and 20.2% of the annual N drainage losses from the plots receiving 100 and 500 kg N ha−1 yr−1, respectively. Loads of soluble organic N were greater than particulate N but there was no significant relationship with fertilizer N input for either fraction. The average annual loss of total organic N in drainage water ranged from 3.5 to 9.1 kg N ha−1. However, this loss cannot explain the large amount of unaccounted for N in calculations of nutrient balances where inputs invariably exceed outputs. In comparison, the average annual loss of organic N from the six river catchments ranged from 4.7 to 8.1 kg N ha−1, which suggested that a large proportion of the organic N in river water was originating from land drainage.

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