Variability of Measured Properties in Morphologically Matched Pedons

Variability in data from morphologically matched pairs of pedons was assessed to establish operational norms in sampling and to consider alternative sampling procedures. Coefficients of Variation (C.V.'s) were computed for the physical properties—percent sand, silt, clay, and 1,500 kPa moisture—and range from 9 to 40% for loess, 23 to 35% for glacial drift, 33 to 47% for alluvium and residuum, 18 to 32% for A and B horizons, and 33 to 51% for C horizons. C.V.'s were computed for the chemical properties—extractable acidity, sum of bases, cation exchange capacity (CEC), base saturation, pH, and organic carbon—and range from 12 to 50% for Alfisols, 4 to 71% for Aridisols, 6 to 61% for Entisols, 10 to 63% for Inceptisols, 9 to 46% for Mollisols, 16 to 132% for Spodosols, 10 to 100% for Ultisols, and 8 to 46% for Vertisols. Cation exchange C.V.'s are directly related to pH dependent charge. On the average, clay content for central concepts of phases of series can be estimated within ± 5% clay (95% confidence level) by 1 to 4 samples in loess soils, 2 to 8 samples in glacial drift soils, and 4 to 24 samples in alluvial and residual soils. Similar estimates of base saturation (sum of cations) within ± 10% (95% confidence level) require 2 samples for Aridisols and Vertisols; 5 for Mollisols; 10 for Alfisols, Ultisols, Entisols, and Inceptisols; and 16 for Spodosols. Vertical distribution of properties and properties of important horizons are efficiently evaluated by sampling one complete pedon plus satellite samples of important horizons from other pedons. To assess a single horizons efficiently, sample only that horizon in several pedons. Sampling of paired pedons is a good first approach technique to study soils in an area.