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This article in SSSAJ

  1. Vol. 62 No. 5, p. 1172-1178
    Received: Apr 28, 1997

    * Corresponding author(s): fxcasey@iastate.edu
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Measurement of Field Soil Hydraulic and Solute Transport Parameters

  1. Francis X. M. Casey ,
  2. Robert Horton,
  3. Sally D. Logsdon and
  4. Dan B. Jaynes
  1. Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
    USDA-ARS, National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011



Agricultural chemical presence in groundwater has drawn attention toward transport processes occurring in soil. Hydraulic conductivity (K) and water-holding capacity of a soil have great influence on water flow and solute transport. However, much of the chemical transport to groundwater can occur through preferential flow pathways. The simplified, preferential flow, mobile-immobile model partitions the water content (θ) into mobile (θm) and immobile (θim) domains, with solute exchange between the domains characterized by the mass-exchange coefficient (α). In this study a sequential tracer application technique was used and K, θ, θim, and α were estimated for a series of pressure heads (H = 10, −30, −60, and −150 mm). This method uses a tension infiltrometer to measure both hydraulic and solute transport parameters in situ. The study took place in a no-till corn (Zea mays L.) field mapped as a Harps series soil (fine-loamy, mixed, mesic Typic Calciaquoll). Unsaturated values of θ and K were distinct from the saturated values. Similarly, though less clear cut, distinctions between saturated and unsaturated values of θim, immobile water fraction (θim/θ), and α were observed. The medians of θ for the sequence of decreasing H values were 0.40, 0.34, 0.34, and 0.33 m3 m-3. The median K values for the same sequence of H were 108, 1.69, 1.51, and 0.72 µm s-1. The median θim/θ values for the H sequence were 0.40, 0.28, 0.25, and 0.39. The median values of α for the H sequence were 0.59, 0.015, 0.0028, and 0.0029 h-1. A strong correlation between α and H suggests a velocity dependence of α.

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