Ultramafic Soils - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 268

Fig. 23.3 Counties containing soils derived from ultrabasic materials

23.5 Factors Influencing the Development
of Ultramafic Soils

The primary factor influencing the genesis of ultramafic soils obviously is
parent material (Table 23.3 ). Ultramafic materials contain an abundance of
Mg and Fe, often at the expense of Ca, K, and other plant nutrients (Proctor
2003 ). This imbalance and the presence of high amounts of trace metals such as
Cr, Ni, Co, and Mn encourages endemic forms of plants (Whittaker et al. 1954 ),
whichinturnplayakeyroleinplantnutritionandpedogenesis(Roberts 1980 ;
Bulmer and Lavkulich 1994 ;Burtetal. 2001 ;Chengetal. 2011 ). Although
ultramafic soils occur in a variety of climates, ultramafic materials in the
USA exist primarily in areas with moderately high precipitation (mean

¼
1,470 mm/yr) and a mild mean annual temperature (12 C). Although ultramafic
soils occur on a variety of slope classes and aspects, topography plays a key role
in pedogenesis of ultraxeric soils through the routing of water (Hseu et al. 2007 ;
Cheng et al. 2011 ) and inducing mass wasting (Lee et al. 2004 ).