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Flux-Controlled Sorptivity Measurements to Determine Soil Hydraulic Property Functions¹

ABSTRACT

Using a new method, the hydraulic diffusivity and conductivity functions D[] and K[h] can be determined over most of their range in about 4 hours. This method uses a series of fast and simple, one-dimensional adsorption measurements for which the cumulative volumes of absorption are controlled proportional to the square root of time with syringes driven by cames. Each combination of motor speed, can size, and syringe size represents an imposed sorptivity for which the water content and/or pressure head at the interface must be measured after they become steady. Steady values are normally reached after only a few minutes. Pressure heads can be recorded during the absorption runs, and at the end a soil sample for gravimetric water content determination can be obtained in about 15 sec. Hydraulic diffusivity and conductivity functions derived from measured sorptivity functions were obtained for a variety of undisturbed and hand-packed soil columns. They all showed excellent agreement with independent data. The flux-controlled boundary resulted in uniform wetting almost every time, whereas previously used potential-controlled boundary conditions often caused nonuniform wetting, which prevented accurate evaluation of sorptivities. The speed, range, and accuracy of this improved version of the sorptivity method compare favorably with other available methods. The method is suitable for routine and large scale use.

¹ Contribution from the U. S. Salinity Laboratory, USDA, Riverside, Calif.

² Soil Scientist, Present address: Department of Soils and Fertilizers, Agricultural State University, Wageningen, The Netherlands.

Received for publication January 19, 1979. Accepted for publication April 18, 1979.

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