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Elemental Variability Within a Sampling Unit¹

ABSTRACT

To determine the magnitude of lateral variability within an area of 1 to 2 m², six profiles were sampled at 0.6 m-intervals at each of three different sites representing loess, till, and outwash deposits. Elemental Ti, Zr, Fe, Ca, and K were determined by X-ray spectroscopy for 50-20µ and 20-5µ fractions of selected horizons within each profile. Coefficients of variation within these deposits ranged from 1 to 13% for Ti, 4 to 20% for Zr, 3 to 20% for Fe, 5 to 13% for Ca, and 2 to 9% for K. The order of variability was loess till < outwash. No consistent differences in elemental variability were observed between size fractions or horizons (i.e. A, B, or C).

Elemental data from a single horizon within a vertical profile will seldom permit mean estimates closer than ±10 to 20% (95% confidence interval) for loess and till deposits, and ±20 to 45% for the more variable outwash deposits. Three lateral subsamples within a given horizon would permit mean estimates of above elements within ±10% in loess and till but 20 subsamples would be required to achieve similar accuracies in some outwash deposits. Such data emphasize the need to multiple subsample horizons in a lateral dimension if mean estimates are to be accurate within 10 to 20% over an area approximating a pedon or sampling pit. The number of subsamples for a given horizon is a function of the element under consideration, nature of deposit, and precision of mean estimate desired.

¹ Contribution from the Dep. of Agronomy, Ohio Agr. Res. and Dev. Center; State Project 371, Journal Paper no. 52–72. Presented before Div. S-9, Soil Sci. Soc. of Amer. Tucson, Ariz., Aug. 24, 1970.

² Instructor and Professor of Agronomy, respectively, Ohio Agr. Res. and Dev. Center. Wooster and Ohio State Univ., Columbus 43210.

Received for publication May 3, 1972. Accepted for publication September 28, 1972.