Calcic and Petrocalcic Horizons - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 111

Fig. 12.3 Counties containing soils with calcic and petrocalcic horizons
12.5 Factors Influencing the Formation of Calcic
and Petrocalcic Horizons
Soils with a petrocalcic horizon receive an average of 392 mm/yr of precipitation
and have a mean annual air temperature of 17.6 C (Table 12.3 ). However, the
current MAP ranges between 127 and 635 mm, and the current MAAT ranges from
12 to 23 C. Soils with petrocalcic horizon were most common in the Sonoran and
Chihuahuan deserts in southwestern USA. The dominant vegetation on soils with a
petrocalcic horizon was short-grass prairie (41 %), followed equally by creosote
bush, mid-grass prairie, and tall-grass prairie. Slopes of soils with a petrocalcic
horizon commonly range from 0 to 10 %. Two-thirds of the parent materials for
soils with a petrocalcic horizon were calcareous alluvium, with the other third being
calcareous aeolian materials. Soils with a calcic horizon are derived primarily from
alluvium (55 %), followed by colluvium (11 %) and residuum (8 %). The vegeta-
tion covers a broad range but includes sage (30 %), mid-grass prairie (22 %), short-
grass prairie (14 %), and creosote bush (10 %).
Organisms may play a key role in the precipitation of carbonates (Monger
et al. 1991 ; Durand et al. 2007 ; Shankar and Achyuthan 2007 ) (Table 12.3 ). Monger
et al. ( 1991 ) found fossilized remains of fungal hyphae in desert soils near Las
Cruces, NewMexico. In a laboratory experiment, they showed that soil bacteria and
fungi precipitated calcite when cultured in a Ca-rich medium. Micromorphological
study of calcic horizons in desert soils of India showed the occurrence of alveolar