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This article in JEQ

  1. Vol. 21 No. 4, p. 602-607
     
    Received: Aug 27, 1991
    Published: Oct, 1992


    * Corresponding author(s):
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doi:10.2134/jeq1992.00472425002100040013x

Nitrogen Outputs from a Field-Size Agricultural Watershed

  1. Richard Lowrance *
  1. USDA-ARS, Southeast Watershed Research Laboratory, P. O. Box 946, Tifton, GA 31793.

Abstract

Abstract

Nitrogen outputs from a 0.34-ha field were measured for 1984 through 1987. The field consisted of Cowarts loamy sand (fine-loamy, siliceous, thermic Typic Hapludult) managed in a summer row crop-winter cover crop sequence. Outputs measured were subsurface flow, surface runoff, and denitrification. Monthly sampling of denitrification rates showed a high degree of temporal and spatial variability. Rates significantly increased with soil moisture and depth. Denitrification also increased after irrigation events. Nitrogen movement in subsurface flow was 97% NO3-N and was about 10 times that in surface runoff. Most subsurface flow and movement of N (77 kg NO3-N ha−1) occurred in December 1986 through February 1987 when 62 cm of precipitation fell in a 12-wk period (December 1986–February 1987) following fertilizer application. This period accounted for one-half the total subsurface nitrate movement for the 4-yr study. Even though no crop was harvested in 1985, subsurface outputs of N were low in winter of 1985–1986. Soil NH4-N levels were significantly higher after the year without a harvest, indicating that more of the N in crop residue was found in the soil pool.

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