Soil Fertility Constraints and Exploratory Multivariate Classification of Appalachian Legacy Coal Mine Soils

Legacy coal-mined lands in the Appalachian coalfield retain chemically heterogeneous soils, but consistent multi-site comparisons are scarce. This study asked whether soil properties differ among sites, which properties structure sample-level variation, and whether samples form distinct soil-chemistry classes. We measured 18 soil-test properties in 135 surface (0–20 cm) samples from seven legacy coal-mined sites in West Virginia and Pennsylvania and analyzed them with Kruskal–Wallis tests (Holm correction), principal component analysis (PCA) of 17 properties, and Ward clustering, with bootstrap resampling and alternative specifications as robustness checks. All 18 properties differed among sites, although boron differences coincided with the laboratory batch. Five components explained 69.9% of the variance; the acidity/base-cation, trace-metal, and phosphorus-availability components were reproducible (Tucker’s congruence ≥ 0.87), but two minor components were not. Clustering separated an acidic, lime-requiring majority (n = 106) from a near-neutral minority (n = 29), but separation was weak (silhouette = 0.27), only the acidic group was stable (Jaccard = 0.90 versus 0.67), and the partition matched a pH threshold of 6.0 across site boundaries. These soils are better described as a continuous acidity gradient with an independent trace-metal dimension than as discrete fertility classes, providing a baseline for designing, but not replacing, field trials of reclamation and bioenergy species.