Fig. 1. Bulk density means as a function of soil depth in (A) Ustolls and (B) Usterts of central South Dakota (USA). Standard errors for Ustolls (N = 6) were 0.032, 0.025, and 0.019 Mg m^–3 at 0.02- to 0.07-, 0.15- to 0.20-, and 0.25- to 0.30-m depth, respectively. Standard errors for Usterts (N = 2) were 0.070, 0.053, and 0.071 Mg m^–3 at 0.02- to 0.07-, 0.15- to 0.20-, and 0.25- to 0.30-m depth, respectively. *Significant (P < 0.05) difference in the orthogonal contrast between grass and cultivated soils. + Significant (P < 0.05) difference in the orthogonal contrast between no-till and till soils.