Cultivated and Adjacent Virgin Soils in Northcentral South Dakota: II. Mineralogical and Micromorphological Comparisons

Abstract

AbstractCultivated and adjacent virgin soils [Williams (fine‐loamy, mixed, Typic Argiboroll) and variants of Williams] from northcentral South Dakota were compared, by horizon, to examine the effects of cultivation on mineralogical and micromorphological properties of the soils. Two major mineralogical differences were noted. Silt‐sized material from the Btk, Bk, and C horizons of a cultivated pedon had smaller calcite‐to‐dolomite peak‐height ratios, as determined by x‐ray diffraction, than similar horizons from a virgin pedon. These findings, combined with the results of additional experimentation, suggest calcite is being leached from Btk horizons and is accumulating in Bk horizons of cultivated pedons. The A, Bt, and Btk horizons of a virgin pedon had more subdued x‐ray peak intensities for the 001 spacing of smectite than similar horizons from a cultivated pedon. When similar horizons of a cultivated and a virgin pedon were compared, micromorphological differences were as follows: (i) the Ap horizon displayed less macroporosity, more diffuse and lighter‐colored organic glaebules, fewer and less pronounced microaggregates, and fewer surface coatings on sand‐sized particles; (ii) the Bt horizon from the virgin pedon had greater macroporosity; (iii) the Btk and Bk horizons of the virgin pedon contained more particles coated with and more composite particles bound with organo‐mineral material; (iv) a far greater proportion of voids were filled with black, opaque cutans in the Btk horizons of the cultivated pedons that, by electron microprobe analysis, was dominantly Si.