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Length of Irrigation and Soil Humidity as Basis for Delivering Fumigants through Drip Lines in Florida Spodosols
  • Bielinski M. Santos
  • James P. Gilreath
  • Timothy N. Motis
  • Gulf Coast Research and Education Center
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 Introduction
  •  Loss of methyl bromide (MBr) as soil fumigant:
    • Search for alternatives,
    • Combinations of broad-spectrum fungicides and nematicides followed by herbicides.

  •  Broadcast and in-bed injections:
    • 1,3-dichloropropene + chloropicrin (1,3-D + Pic),
    • Metam sodium (MNa).
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 Introduction
  •  Application of any MBr alternative requires the maximum possible coverage of soil volume.


  •  Unfortunately, this is not always possible, thus pest control gaps are frequently observed.
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 Introduction
  • Therefore, more efficient delivery systems need to be developed.


  •  Drip application reports:
    • Telone-C35®, Inline®, liquid and granulated MNa, and iodomethane + Pic (60:40) » MBr,


    • Inline® + MNa, Telone-C35® + MNa, and Telone II® + MNa » MBr.
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 Introduction
  • Scattered research has been conducted under Florida conditions on this subject.


  • Benefits:
    • Reducing soil and water pollution,
    • Reducing personnel poisoning/exposure.
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 Introduction
  • Soil texture has a close relationship with waterfront movement in the soil profile.


  • Heavy to loamy soils have slow infiltration:
    • Greater opportunities for liquid formulations to move laterally, thus increasing coverage.
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"45"
  • 45% coverage
  • 12 h
  • Single drip tube
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"85"
  • 85% coverage
  • 10 h
  • Two drip lines
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 Objetives
  • Determine the impact of soil humidity on the extent of water coverage obtained through varying irrigation times.
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"Two field trials"
  • Two field trials;


  • January and March 2003 at GCREC;


  • EauGallie fine sand;


  • 1.0% organic matter and pH 7.3;


  • Raised beds were pressed with a bedder;


  • Beds covered with low-density plastic mulch.
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"Beds"
  • Beds: 0.71 m wide (top) x 0.81 cm wide (bottom) x 0.20 m high (cross sectional area of 0.15 m2);


  • Two drip irrigation lines (T-Tape® Systems);
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  Materials and Methods
  • Split-plot design with 3 and 6 replications for January and March trials, respectively.


  • Factors:
    • Main plots: Soil water contents of 7% (field capacity) and 20% (saturation).
    • Subplots: Lengths of irrigation were 2, 4, 6, 8 and 10 h.

  • Water table maintained 0.45 m below bed surface.
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"Water-soluble blue marking dye"
  • Water-soluble blue marking dye.
  • One week after dye application, plastic mulch was removed and cross sections were exposed at the emitters.
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  Materials and Methods
  • High resolution digital pictures were taken of each section.


  • Images were transferred into a photographic software and covered areas were determined.


  • Regression analysis (P=0.05).
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 Conclusions
  • 7% humidity:
    • 82% wetting area in 10 h.


  • 20% humidity:
    • 90 and 94% wetting area in 8 and 10 h.

  • Therefore, soil water status has an influence over water distribution patterns throughout planting beds.
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 Conclusions
  • This might allow scientists to redesign strategies for drip-applied fumigants in Florida spodosols.


  • Further studies:
    • Determine if differences in coverage reflect on yields or soilborne pest and weed control,


    • Assess the effect of increased wetting and fumigant diffusion beyond waterfronts.