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Journal of Environmental Quality Abstract -

Denitrification in Subsoils of the North Carolina Coastal Plain as Affected by Soil Drainage1


This article in JEQ

  1. Vol. 4 No. 3, p. 311-316
    Received: Oct 16, 1974

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  1. R. P. Gambrell,
  2. J. W. Gilliam and
  3. S. B. Weed2



In a tiled moderately well-drained soil, over 200 kg NO3-N/ha were generally found distributed throughout the top 3 m. However, in a poorly drained soil, relatively low levels of NO3 were found in the top m and very little NO3 persisted in the saturated zone beneath 1 m.

Oxidation-reduction potential (Eh) measurements in the tiled moderately well-drained soil indicated well-oxidized conditions (500–700 millivolts) to 3 m. The Eh measurements beneath 1 m in the poorly drained soil consistently indicated favorable conditions for denitrification. A marked decrease in the NO3-N/Cl ratio with depth in the poorly drained soil supported the contention that denitrification was occurring in the soil.

The water-soluble C content of the subsurface soil water was 2–5 mg/liter in the moderately well-drained soil and 10–15 mg/liter in the poorly drained soil. The absence of saturated conditions for extended periods of time and lack of an adequate energy source apparently limited denitrification in the moderately well-drained soil and much of the fertilizer N not utilized by crops moved into shallow aquifers and surface water. However, sufficient available organic C was present in the subsoil of the saturated, poorly drained soil to bring about a reducing soil environment and subsequent denitrification of the residual NO3. Thus, little NO3 moved from this soil into surface waters.

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