Use of Extractable Iron as a Differentiating Criterion for Soil Series Separation.
Shawn McVey, USDA-NRCS and The Univ of Connecticut, 344 Merrow Road, Suite A, Tolland, CT 06084-3917, Harvey D. Luce, Dept of Plant Science, The Univ of Connecticut, Storrs, CT 06268-4067, and Thomas Morris, Univ of Connecticut, 1376 Storrs Rd; U-4067, Plant Science, Storrs, CT 06269.
Separation of Brimfield and Brookfield soil series from their competing series based primarily on parent material and color hue has proven difficult. The objective of this study is to examine the value of extractable iron in separating Brimfield (Loamy, mixed, mesic active Lithic Dystrudepts) and Brookfield (Coarse-loamy, mixed, mesic, active Typic Dystrudepts) soil series from their competing series (Lithic and Typic Dystrudepts). A second objective is to test the hypothesis that these soils may actually be Post-Active Acid Sulfate soils (PAAS). A model was developed with Arc View v3.3 to identify currently mapped Brimfield and Brookfield soils and probable areas of mismapped competing series in Connecticut and Massachusetts. Forty pedons were sampled and characterized through the National Cooperative Soil Survey Program. Initial results for the particle size control section indicate significant differences in mean dithionite-citrate extractable iron (Fed) of 3.11% PAAS and 0.76% in competing series, with 2.40% in mis-mapped competing series (probable PAAS). Extractable iron ratios of Fed to ammonium oxalate extractable iron (Feo) were 15.31 for PAAS, 8.25 for probable PAAS, which differed significantly from the 3.29 ratio for competing series. Cross-validation summary from discriminate analysis for the particle size control section mean indicates using only 2 variables, Fed and the ratio of Fed:Feo, can properly classify these soils into the proper groups 93% of the time. Additionally, mean pH by CaCl2 differed significantly between groups of soils with pH 4.2 for PAAS and probable PAAS and 4.4 for the competing series. PAAS contain a greater content of Fed compared with competing series. Mean Fed, Feo:Fed, and pH (CaCl2) support the hypothesis that Brimfield and Brookfield series are distinctly different from their competing series, are PAAS, and may be separated from competing series by extractable iron. This work is supported by USDA Natural Resources Conservation Service (NRCS).