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This article in SSSAJ

  1. Vol. 61 No. 4, p. 1030-1036
    Received: July 12, 1996

    * Corresponding author(s): fxcasey@iastate.edu
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Immobile Water Content and Mass Exchange Coefficient of a Field Soil

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



Determining the preferential flow characteristics of a soil is important because agrichemicals can contaminate groundwater via preferential flow pathways. A model that predicts solute transport due to preferential flow is the mobile-immobile solute transport model, which partitions the total water content (θ, m3 m−3) into a mobile fraction (θm) and an immobile fraction (θim). Recently, an in situ method was proposed for determining the mobile-immobile model parameters of θim and mass exchange coefficient (α) between the fractions by using a tension infiltrometer to apply a series of four fluorobenzoate tracers. The objective of this study was to test the in situ technique at 47 sites along a transect in a ridge-till corn (Zea mays L.) field of Nicollet soil (fine-loamy, mixed, mesic Aquic Hapludoll). The immobile fraction (θim /θ) ranged from 0.394 to 0.952 with a median of 0.622. The mass exchange coefficient ranged from 0.000237 to 0.00481 min−1 with a median of 0.00123 min−1. These values are similar in magnitude and range to values reported by other investigators, and they follow the same relationships. The values of θim/θ and α along the transect indicated no obvious spatial trends or spatial correlations. Significant linear correlations did exist between α and soil water flux, α and θim, and θ and θim.

Journal Paper no. J-16868 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, IA, Project no. 3287, and supported by Hatch Act and state of Iowa funds.

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