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Soil Science Society of America Journal Abstract -

Multiple Tensiometer for Determining the Vertical Component of the Hydraulic Gradient in Soil1


This article in SSSAJ

  1. Vol. 18 No. 1, p. 7-10
    Received: June 25, 1953

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  1. L. A. Richards2



A description is given of an instrument for measuring the hydraulic head and hydraulic gradient of water in unsaturated field soil. Porous ceramic sections are mounted between plastic spacers to make a rod-shaped instrument for insertion in a hole made by the Standard Veihmeyer soil sampling tube. Five porous sections with a vertical spacing of 10 cm, are thus arranged with individual connections to mercury manometers mounted at the top of the assembly.

During infiltration, after 44 cm of water had entered a deep, uniform, fine sandy loam, the downward hydraulic gradient averaged 1.3 in the 10–30 cm depth interval. This corresponds to a downward water-moving force of 1.3 g. Six days later, a few hours after a 1-cm rain, the average downward water-moving force in the same depth interval was 5 g. Four days after the rain, there was a net upward water-moving force of 36 g in the 10–20 cm depth interval, due to the influence of surface evaporation. A much higher value existed in the 0–10 cm layer because of the greater moisture gradient near the soil surface.

The term static zone is used in connection with the soil-water system to designate the locus of points above which water movement is upward, and below which water movement is downward. A static zone passes downward through fallow soil following wetting. Over a four-day period of warm dry weather following a heavy irrigation, the static zone passed downward at an average rate of 6 cm per day in a fallow fine sandy loam.

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