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Published in Soil Sci Soc Am J 46:20-26 (1982)
© 1982 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Soil Hydraulic Properties as Stochastic Processes: II. Errors of Estimates in a Heterogeneous Field1

David Russo and Eshel Bresler2

ABSTRACT

Results of integral scales and coefficient of variations (C.V.) from Part I are applied to evaluate errors in estimating average values of several hydraulic properties. Based on the Ergodic Hypothesis and on standard statistical theory, an equation is derived to calculate the total field area and number of measurements needed to estimate (for a prescribed error) ensemble averages of a given hydraulic property. For a 0.8-ha field performing 90 measurements to estimate mean values of various hydraulic properties, the errors are in the range between 7 and 46%. Various combinations of number of integral scales (I) and number of measurements (N) are used to estimate mean values of a given hydraulic property with a given error. An "optimal" I-N combination is derived. With this approach, 4 to 156 integral scales and 2 to 190 measurements are needed to estimate mean values of the various hydraulic properties with 20% error. The kriging technique and fictitious point method are used to evaluate number and locations of additional observation points needed to estimate mean value of the saturated hydraulic conductivity (Ks) over a finite field with a given accuracy. To obtain the C.V. of Ks of 2.5%, nine additional points are required.

Key Words: soil water retentivity • spatial variability • integral scale • kriging

NOTES

1 Contribution from the A.R.O., The Volcani Center, Bet Dagan, Israel. No. 237-E, 1979 Series.

2 Graduate Research Assistant and Soil Physicist, respectively, Division of Soil Physics, A.R.O., Bet Dagan, Israel.

Received for publication September 20, 1979. Accepted for publication August 15, 1981.






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