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A Sampling Study in a Saline and Alkali Area¹

ABSTRACT

A study was made in the Baker Valley Area, Oregon, to determine by statistical analysis the variation in conductivity and exchangeable-sodium percentage (ESP) between soil mapping units and between locations within soil mapping units.

The variation between soil mapping units was significant at the 1% level for both conductivity and ESP. This would imply that there is a distinct difference between soil mapping units. The sample variation within locations and the location variation within soil mapping units were not large for soil conductivity but were quite large for ESP, particularly the individual sample variation. This indicates that for ESP the difference in the subsamples taken at one sampling location which make up a composite sample may vary as much or more than the samples taken over an area to represent a particular soil mapping unit.

It was shown that the variance of the mean may be reduced either by increasing the number of samples per location or by increasing the number of locations; the latter reducing the variance more rapidly. As the cost of moving from one location to another increases relative to the cost of processing a sample, the sampling rate per location should be increased.

¹ Technical Paper No. 1095, Oregon Agr. Exp. Sta. This work includes a portion of a thesis presented by the senior author in partial fulfillment of the requirement for the M.S. degree at Oregon State College. The senior author was supported by a scholarship from the Ford Foundation while on leave from the A.U.B., Beirut, Lebanon.

² Formerly Graduate Student, Oregon State College, now Instructor of Soils, American University of Beirut, Beirut, Lebanon; Asst. Professor of Soils; and Exp. Sta. Statistician, respectively.

Received for publication December 27, 1957. Accepted for publication February 7, 1958.