Gypsic and Petrogypsic Horizons - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 176

Fig. 17.2 Frequency distribution of soil series with a gypsic horizon in various families
density, ranging from 1.08 to 1.37 g/cm 3 and averaging 1.20 g/cm 3 .SoilOC
concentrations in gypsic horizons are low, ranging from 0.65 to 0.08 % and averaging
0.20 %. The cation-exchange capacity of the gypsic horizon is low, averaging
3.6 cmol c /kg soil. The sodium adsorption ratio (SAR) is low as Ca tends to be the
dominant exchangeable cation. For the pedons included in this study, the CaSO 4
concentration of the gypsic horizon averaged 63 %. The mean electrical conductivity
value and CaCO 3 concentration was 6.5 dS/m and 8.1 %, respectively.
17.3 Classification of Soils with Gypsic and Petrogypsic
Horizons
Soils with a gypsic or petrogypsic horizon occur in two orders, six suborders,
12 great groups, 28 subgroups, and 133 soil series (Table 17.2 ). Soil series with a
gypsic horizon are most abundant in the Aridisol order (122 series), followed by the
Inceptisols (5), Vertisols (5), and Mollisols (1 soil series).