Soil Geography - Zonal, Intrazonal and Azonal Soils (Older System of Classification)

Soil geography deals with the distribution of soils as function of the five recognized soil-forming factors (climate, flora and fauna including Man, relief, parent material, time), either acting singly or in combination. It forms the basis of such concepts as zonality (i.e. the regional distribution of soils in zones), first formulated by Dokuchaev on the basis of climate for European Russia, elaborated upon further by Glinka and Sibirchev, who introduced the zonal, intrazonal and azonal soils approach, taking into account other soil-forming factors than climate.

The loose material or the upper layer of the Mantle Rock, the soil system, is the product of environmental and biological processes in interrelation with climate, vegetation (flora), animals (fauna), underlying rocks, topography and time which affect the biosphere.

This is the Zonal (Older) System of Classification. This system links the distribution of various soil types to the distribution of climate and vegetation.

Zonal Soils: The zonal soils are formed on normal sites from ordinary siliceous rocks and show clearly the impress of climate and vegetation. In short, these are formed under conditions of good soil drainage through the prolonged action of climate and vegetation, e.g. chestnut soils. This kind of soils have following types -

1. Tundra Soils
2. Podzols
3. Brown Forest Soils
4. Laterite Soils/Latosols/Ferralsols
5. Chernozem/Prairie/Steppe
6. Grumusol/Reddish Brown Soils
7. Desert (Seirozems and Red Desert) Soils

Revision Point - Zonal soils are characterised by the dominant influence of climate.

Intrazonal Soils: The intrazonal soils include the soils from less common parent materials and those influenced by high ground water or  under conditions of very poor drainage (such as in bogs, flood-plain meadows, or in the playa lake basins of the deserts) or upon limestone. Depending on the role played by water, presence of calcium in the parent material and the location, intra-zonal soils may be -

1. Hydromorphic
2. Calcimorphic 
3. Halomorphic

Revision Point - Intra-zonal soils have some local factor like moisture or parent rock having the dominant influence. The intra-zonal soils occur within broad zonal types on poorly draining sites.

Azonal Soils: The azonal soils are youthful, owing to recent renewal by sedimentation or erosion. This have no well-developed profile characteristics. These soils are common where the parent material is being continuously eroded and deposited, e.g. alluvial Soils (newer or younger Khadar and older Bhangar soils) or lithosols (those at high altitudes on resistant parent material). These soils have poorly developed horizons due to three reasons:

• Lack of Time For instance, in new flood plains alluvium is being continually eroded and deposited.
• Parent Material Azonal soils like ‘regosols’ result from loose sand and loess.
• Geomorphology ‘Lithosols’ result on steep slopes where soil is eroded as soon as it is deposited.

Revision Point - Azonal soils are poorly developed and occur along the recent alluvium, steep slopes or sand deposits.

Table: Classification of Soils

Major Soil Classification	Sub-Orders	Soil Groups
Zonal Order	Suborder-I Light coloured podzolized soils of the forested regions.	Podzol Soils, Brown Podzolic soils, Grey Brown Podzolic Soils, Red-Yellow Podzolic Soils.
	Suborder-II Lateritic soils of warm moist tropical and equatorial regions.	Latosols: Reddish-brown Lateritic Soils, Black and Dark Grey Tropical Soils.
	Suborder-III Soils of forest-grassland transitions. Dark coloured soils of semiarid, sub-humid and humid grasslands.	Degraded Chemozems. Prairie Soils, Reddish Prairie Soils, Chemozem Soils, Chestnut Soils, Reddish Chestnut and Reddish-Brown Soils.
	Suborder-IV Light coloured soils of deserts.	Brown Soils. Grey Desert soils (Sierozems) and Red Desert Soils.
Intrazonal Order	Suborder-I Hydromorphic soils of marshes, Swamps, bogs and flat uplands.	Bog Soils, Meadow Soils, Alpine Meadow Soils, Planosols.
	Suborder-II Halomorphic soils of poorly drained and regions and coastal deposits, Calcimorphic soils.	Saline soils, Alkali soils, Soloth, Rendzlna soils.
Azonal Order (Lithosols)	Suborder Regosols	Alluvial soils, Dry sands.
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