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Table 26.2 Influence of soil-forming factors on development of diagnostic horizons
Horizon
Climate
Organisms
Relief
Parent material
Human
Time (kyr)
Epipedon
Ochric
[All]
[All]
[All]
[All]
Mollic
Grassland, steppe
Base rich
>
0.5
Umbric
Cool, humid
Low-base
>
0.5
Histic
P
ET
Peatlands
Depressions
0.5
>
>
Melanic
Abundant precip.
Volcanic, Si rich
3.0
>
Folistic
Abundant precip.
Forest
Steep, well drained
Anthropic
Manuring
Plaggen
Cultivation
Subsurface horizon
Argillic
P
ET
Lith. discontin.
2.0
>
>
Cambic
[All]
[All]
[All]
[All]
0.1
>
Calcic
P
ET
Ca rich
6.0
<
>
Kandic
P
ET
Forest
Low-activ. clays
10(?)
>
>
Albic
Aquic
0.1
>
Duripan
P
ET
Grassland
Volcanic, Si rich
130
<
>
Spodic
P
ET
Coniferous, ericac.
Fe rich
1.0
>
>
Glossic
Lith. discontin.
Fragipan
P
>
ET
Forest
Silt rich
>
18
Natric
High SAR; smectitic clays
>
6.0
Gypsic
<
400 mm/yr
Excess drained
Gypsiferous
>
6.0
Salic
P
<
ET
Poor drainage
>
0.5
>
1,500 mm/yr;
>
24
C
Oxic
Trop forest, savanna Well drained
>
2,000
Ortstein
>
800 mm/yr
Coniferous, ericac.
Seasonal high watertable
Fe rich
>
2.0
Petrocalcic
P
<<
ET
Microbial fibers
Ca-rich eolian, alluvium
>
200
Placic
>
2,400 mm/yr
Depressions, aquic
>
0.5(?)
Petrogypsic
<
400 mm/yr
Excess drained
Gypsiferous
>
200
Agric
Cultivation
Sombric
1,000 mm/yr
Trop mtn.
>
1,500 m elev.
>
100(?)
>
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