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Simple Field Methods for Estimating Soil Hydraulic Conductivity¹

ABSTRACT

Soil water content profiles monitored as a function of time following steady-state infiltration conditions in a field soil provide the only data necessary to estimate the soil hydraulic conductivity as a function of soil water content. For two proposed methods, it is assumed that water redistributes only in response to the gravitational field and that the hydraulic conductivity is an exponential function of soil water content. Experiments were conducted on three fallow field soils covered with plastic to prevent evaporation and sampled to depths of nearly 2 m. Values of hydraulic conductivity calculated by both the two proposed methods as well as by a third recently reported method were compared with those calculated by integrating Richards' equation without simplifying assumptions. Although the above comparisons at given sites within a field revealed that the three methods may sometimes yield poor estimates of the hydraulic conductivity, distributions of observed values averaged over the entire field were statistically comparable for 20 observations. It is concluded that a greater number of observations made possible by simplifying assumptions, and hence, less instrumentation and cost, is preferable to fewer observations with more exact methods that are not as amenable to statistical analyses over larger land areas.

¹ Contribution of the Center for Nuclear Energy in Agric. (CENA) of the Univ. of Sao Paulo and Escola Superior de Agricultura "Luis de Queiroz" (ESALQ), Piracicaba, Brazil; and the Dep. of Land, Air and Water Resources (LAWR), University of California, Davis, CA 95616.

² Research Scientist at CENA; Professor of Physics and Meteorology at CENA and ESALQ; and Professors of Water Science at LAWR, respectively.

Received for publication July 23, 1979. Accepted for publication August 28, 1979.