Elemental Variability Within a Sampling Unit1
- L. R. Drees and
- L. P. Wilding2
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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