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Spatial Extrapolation of Soil Characteristics Using Whole-Soil Particle Size Distributions

^a Western Ecology Division, NHEERL, U.S. Environmental Protection Agency, 200 S.W. 35th Street, Corvallis, OR 97333
^b OAO Corporation, 200 S.W. 35th Street, Corvallis, OR 97333

View larger version (38K): [in a new window]   Fig. 1. A schematic presentation of data aggregation and relationships with soil characteristic (SC) models. Soil loss tolerance factor, erodibility, the high and low ranges of seven soil SCs are aggregated from layers (top left box) to a pedon, plus the high and low ranges of three SCs are aggregated again from pedons (top right box) to a map unit SC. Models defined by the equations for conditional expectations are produced separately for each SCq in each USDA5 texture class using the odd-numbered map units (lower left boxes). Each SC model is tested two ways: an interpolation test (not shown here) verifies the assumption of grouping by the whole-soil particle size distribution (PSD) statistics (dg and g) and an extrapolation test (arrow from lower right box) predicts the SCq of the even-numbered map unit groups (MUGs)

View larger version (29K): [in a new window]   Fig. 2. The USDA5 texture trajectory system showing 30 map unit groups (MUGs) and number of map units, shaded circles (A), the high and low ranges of soil available water capacity (B), and cation exchange capacity (C) in shaded triangles. cr = coarse-textured soils, fn = fine-textured soils, mecr = medium coarse-textured soils, mocr = moderately coarse-textured soils, mofn = moderately fine-textured soils