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This article in SSSAJ

  1. Vol. 73 No. 3, p. 1044-1052
     
    Received: June 10, 2008
    Published: May, 2009


    * Corresponding author(s): shinjiro@ifas.ufl.edu
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doi:10.2136/sssaj2008.0206

Spatial and Temporal Distributions in Sandy Soils with Seepage Irrigation: I. Ammonium and Nitrate

  1. Shinjiro Sato *a,
  2. Kelly T. Morgana,
  3. Monica Ozores-Hamptona and
  4. Eric H. Simonneb
  1. a Southwest Florida Resear. and Educ. Center, Univ. of Florida, 2686 State Rd. 29 N, Immokalee, FL 34142
    b Horticultural Sciences Dep., Univ. of Florida, 1241 Fifield Hall, Gainesville, FL 32611

Abstract

Tomato (Lycopersicon esculentum Mill.) in southwest Florida is typically grown on fumigated, raised beds with polyethylene mulch under seepage irrigation. An average grower's N rate currently exceeds the University of Florida's Institute of Food and Agricultural Sciences (UF-IFAS) recommendation (224 kg N ha−1 maximum). Excess nutrients are subject to runoff and leaching, which raises environmental concerns in Florida watersheds. A field study was conducted to elucidate N spatial distribution in tomato beds during the 2006 spring and winter growing seasons with 224 and 358 kg N ha−1 rates. Ammonium N was highest for both seasons during 0 to 1 wk after planting (WAP) at the 0- to 10-cm depth in the fertilizer band, but rarely moved vertically. Lateral movement of NH4 +–N was observed through 7 WAP, however, probably due to diffusion. Nitrate N at 0 to 10 cm in the band peaked during 3 to 4 WAP, indicating about 3 wk of nitrification in the spring; however, this process was shortened to 1 to 2 wk in the winter, probably due to greater bacterial activity with warmer temperatures in the beginning of the winter than the spring (average 8°C in the first 3 wk). Both lateral and vertical movements of NO3 –N were observed in the spring, even at the 20- to 30-cm depth. A rise and subsequent fall of the water table level during 5 to 8 WAP particularly enhanced NO3 –N downward movement, which was attributed to greater diffusivity of NO3 –N than NH4 +–N. Minimizing water table fluctuations and applying a reduced N rate are critical to reduce NO3 –N leaching loss.

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