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This article in SSSAJ

  1. Vol. 39 No. 3, p. 424-430
     
    Received: Apr 11, 1974
    Published: May, 1975


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doi:10.2136/sssaj1975.03615995003900030021x

A Field Study of Soil Water Depletion Patterns in Presence of Growing Soybean Roots: I. Determination of Hydraulic Properties of the Soil1

  1. L. M. Arya,
  2. D. A. Farrell and
  3. G. R. Blake2

Abstract

Abstract

The hydraulic properties of a Waukegan loam profile were determined by field and laboratory procedures. Pressure-water content relationships obtained in the laboratory were found to be variable at pressures above −100 cm of water. In this range field data were considered more reliable.

Hydraulic conductivity in the field was determined from flux and hydraulic-head gradient data. Hydraulic-head gradients were obtained from tensiometric measurements of pressure at various depths. In the soil profile that was subject to both evaporation and drainage, the position of a downward moving “zero flux” boundary was determined. Flux across any depth was obtained by integrating the rate of change of water content with time between the “zero flux” boundary and the depth in question.

A modified laboratory technique was used to determine the diffusivity of undisturbed soil cores. Water content vs. distance data were obtained subject to the conditions that evaporation was proportional to the square root of time and the soil core was effectively semi-infinite. A diffusivity equation developed by Bruce and Klute (1956) was used to calculate diffusivity from the water content-distance functions. Diffusivities were converted to conductivities.

The “zero flux” boundary technique greatly reduced the time needed by covered plot methods to obtain conductivities at high soil-water pressures. The laboratory procedure required only about 30 min/sample and gave results that compared favourably to field results.

At high water contents and to a depth of 20 cm, field conductivities were slightly lower than laboratory estimates. Below the 20-cm depth field data tended to be slightly higher.

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