Inorganic Nitrogen in Drainage Water from Grazed Grassland in Northern Ireland
- C. J. Watson *,
- C. Jordan,
- S. D. Lennox,
- R. V. Smith and
- R. W. J. Steen
Agricultural and 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; Dep. of Agric. and Environ. Science, The Queen's University of Belfast, Newforge Lane, Belfast, BT9 5PX, Northern Ireland; Agricultural Research Inst. of Northern Ireland, Large Park, Hillsborough, County Down, BT26 6DR. Abstract
The loss of inorganic N in drainage water from grazed perennial ryegrass (Lolium perenne L. cv. Talbot) swards in Northern Ireland was studied for 9 yr. Plots (each 0.2-ha area) were hydrologically isolated and artificially drained to V-notch weirs with flow-proportional monitoring of drainage water. Nitrogen, as calcium ammonium nitrate, was applied at 100, 200, 300, 400, or 500 kg N ha−1 yr−1. The efficiency of flow interception by drains decreased on average by 39% during the 9 yr. Annual loss of NO−3 in drain flow for the plot receiving 300 kg N ha−1 yr−1 ranged from 16 to 52 kg N ha−1 and was highest after a dry summer. In individual years, NO−3 in drainage water was linearly related to fertilizer N input with 5 to 23% of the added N input being lost. The shape of the NO−3 dose-response curve did not change with time. Annual losses of NH+4 and NO−2 in drainage water were not related to fertilizer rate, and ranged from 0.2 to 4 kg N ha−1 and 8 to 540 g N ha−1, respectively. Annual flow-weighted mean NO−3, NH+4, and NO−2 concentrations usually did not exceed the European Community maximum admissible limits for drinking water below a fertilizer N application rate of 300 kg N ha−1 yr−1. However, the European Community guideline NH+4 and NO−2 concentrations in salmonid and cyprinid waters were exceeded at application rates ≥100 kg N ha−1 yr−1.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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