Classification and Distribution of Soil Types

Desert soils are Rajasthan's most extensive soil category, covering approximately 61% of the state's 3.42 lakh km² area. They are predominantly aeolian (wind-transported) sands classified as Entisols and Aridisols in the USDA Soil Taxonomy adopted by ICAR.

Geographic extent: Jaisalmer, Barmer, Bikaner, Jodhpur (western part), Sri Ganganagar, Hanumangarh, Nagaur, Pali (western margins), Sikar (western areas), Churu, Jhunjhunu (western portions).

Characteristics:

• Texture: Coarse sandy to loamy sand; low clay content (< 5–8%)
• Colour: Light yellow to buff
• Organic matter: Extremely low (< 0.5% humus)
• pH: 7.5–8.5 (alkaline to moderately alkaline)
• Depth: Highly variable — deep sand dunes to shallow stony crusts
• Caliche layer: calcium carbonate accumulates at 30–60 cm depth in less arid sub-types, limiting root penetration
• Water-holding capacity: Very low; severe drought susceptibility
• Micronutrients: Deficient in zinc (Zn), manganese (Mn), and organic nitrogen

Agricultural potential: Poor without irrigation. IGNP (Indira Gandhi Nahar Pariyojana) has converted significant areas of desert soil in Bikaner, Jaisalmer, and Hanumangarh for wheat, cotton, mustard, and citrus cultivation. CAZRI's sand dune stabilisation programme uses grasses (Lasiurus sindicus — sewan grass) and trees (Prosopis cineraria — khejri) to reduce wind erosion on active dunes.

3.2 Alluvial Soils — (Inceptisols / Entisols)

Alluvial soils are deposited by river systems and occupy the eastern and southeastern plains of Rajasthan — roughly 23% of the state's area. These are Rajasthan's most agriculturally productive soils.

Geographic extent: Alwar, Bharatpur, Sawai Madhopur, Karauli, Dholpur, Tonk, Ajmer (eastern), Jaipur (eastern), Kota, Bundi (river valleys), Dausa, Sikar (eastern belt). Major river corridors: Chambal, Banas, Gambhir, Banganga, Parbati.

Sub-types:

• Khadar: New alluvium, deposited by annual floods; fine-textured, fertile, higher moisture retention.
• Bangar: Old alluvium, higher terrain, well-drained; slightly lower fertility than khadar; often contains kankar (calcium carbonate nodules) at depth.

Characteristics:

• Texture: Sandy loam to silty clay loam
• Organic matter: Moderate (0.5–1.5%) — higher than desert soils
• pH: 7.0–8.0 (neutral to slightly alkaline)
• Nutrients: Rich in potassium; deficient in nitrogen and phosphorus (require fertilizer inputs)
• Water-holding capacity: Good to moderate
• Depth: Generally deep (1–3 m)

Agricultural significance: Eastern alluvial zone produces Rajasthan's principal rabi crops — wheat, mustard, coriander — and kharif crops soybean and maize. The Chambal Command Area (Major Irrigation Project) in Kota, Bundi, and Sawai Madhopur districts irrigates ~4.73 lakh ha of alluvial land. See Topic #87 for crop-specific data.

3.3 Red Soils — (Alfisols / Ultisols)

Red soils derive their characteristic colour from ferric oxide (Fe₂O₃) — iron compounds released during the weathering of Precambrian gneissic and schistose rocks. They occupy approximately 3.5% of Rajasthan's area.

Geographic extent: Dungarpur and Banswara districts (primary concentration), southern Chittorgarh, southern Rajsamand, parts of Udaipur district — essentially the Vagad region of the Mewar-tribal belt.

Characteristics:

• Texture: Sandy loam with ferruginous concretions; gravelly sub-surface
• Colour: Red to reddish-brown; yellowish when hydrated
• Organic matter: Low to moderate
• pH: 6.0–7.5 (slightly acidic to neutral — unlike most Rajasthan soils which are alkaline)
• Nutrient status: Deficient in nitrogen, phosphorus, calcium, and humus; relatively rich in iron and aluminium
• Depth: Shallow to moderate; rocky sub-strata common

Agricultural challenges: Thin profile and poor water retention make red soils drought-prone. Dungarpur and Banswara receive 800–1,000 mm annual rainfall (adequate moisture), but the soils' low water-holding capacity limits productivity. Tribal communities practice rain-fed agriculture — maize, groundnut, and minor millets. Irrigation from small rivers (Mahi, Som, Jakham) partially compensates.

3.4 Laterite Soils — (Oxisols / Ultisols)

Laterite soils form under intense tropical weathering conditions where high rainfall and temperature cause silica leaching, leaving behind concentrations of iron and aluminium oxides. They represent a very small proportion (< 1%) of Rajasthan's soils.

Geographic extent: The highest-rainfall margins of southern Rajasthan — specifically the Phulwari ki Nal and Sitamata wildlife reserve belts of Udaipur district, Sirohi's Abu Road zone (near Mt. Abu — over 1,500 mm annual rainfall), and Pratapgarh district.

Characteristics:

• Hard when dry (laterite blocks used as building material in some areas)
• Low silica, high iron and aluminium oxides
• Very low in plant nutrients; acidic pH (5.0–6.5)
• Poor for food crops without heavy amendment

Economic note: Laterite stone has historically been quarried for construction (traditional buildings in tribal areas). Soil suitability is primarily for teak and mixed deciduous forest, not food crops.

3.5 Black Soils (Regur) — / (Vertisols)

Black soils, classified as Vertisols in USDA/ICAR taxonomy, are among Rajasthan's most agriculturally significant soils in the southeastern plateau region. They derive from Deccan Trap basalt that extended into the Hadoti plateau.

Geographic extent: Kota, Bundi, Baran, Jhalawar districts — the "Hadoti region"; also southeastern Chittorgarh and parts of Sawai Madhopur. This belt coincides with the influence zone of Deccan volcanism.

Characteristics:

• Texture: Heavy clay (montmorillonite clay mineral); very fine-grained
• Colour: Dark grey to black (high iron and magnesium content)
• Key property: Self-mulching — expands and swells when wet; contracts and cracks when dry. The cracking helps incorporate organic matter.
• pH: 7.5–8.5 (neutral to slightly alkaline)
• Nutrient status: Rich in calcium, magnesium, and iron; deficient in nitrogen, phosphorus, and organic matter
• Water-holding capacity: Very high; retains moisture long after monsoon — suited to dry-spell agriculture
• Depth: Generally deep (1–2 m), occasionally shallow on hillsides

Agricultural significance: Black soils support Rajasthan's soybean belt in Kota and Baran districts — Rajasthan is India's 3rd largest soybean producer, almost entirely from this zone. Cotton, mustard, chickpea, and sorghum are major crops. The Kota Barrage and Chambal Command Area irrigation enhances productivity of this already moisture-retentive soil.

3.6 Brown / Forest Soils — / (Inceptisols / Alfisols)

Brown/forest soils develop under natural forest cover on the slopes and ridges of the Aravalli range and the Vindhyan plateau margins. They represent a small but ecologically important soil category.

Geographic extent: Aravalli hill tracts across Sirohi, Pali, Rajsamand, Udaipur, Chittorgarh, Ajmer (Pushkar, Taragarh hill), Alwar (Sariska forest), and the Vindhyan borderland of Kota and Baran.

Characteristics:

• Colour: Brown to reddish-brown
• Texture: Sandy loam to loamy; well-drained on slopes
• Organic matter: Moderate to high (under forest cover) — 1.5–3.0%
• pH: 6.5–7.5
• Depth: Shallow to moderate; rocky outcrops frequent
• Nutrients: Better nitrogen and humus than desert/red soils but limited by shallow profile

Land use: Primarily under reserved and protected forests (Sariska Tiger Reserve, Phulwari ki Nal, Kumbhalgarh Wildlife Sanctuary). Limited agriculture exists in forest clearings. Aravalli afforestation programmes (Forest Department + MGNREGA convergence) aim to restore degraded Aravalli slopes and prevent further topsoil erosion.

3.7 Saline-Alkaline Soils — - (Salids / Natrustalfs)

Saline-alkaline soils form where salts (especially sodium chloride, sodium sulphate, sodium carbonate) accumulate either from: (a) natural inland drainage basins (continental saline lakes), or (b) human-induced secondary salinization from improper irrigation.

Geographic extent:

• Natural saline soils: Around the Sambhar Lake (— Jaipur/Nagaur), Didwana (Nagaur), Degana (Nagaur), Pachpadra (Barmer), Phalodi (Jodhpur), Lunkaransar (Bikaner) — the inland saline lake belt of the Shekhawati-Marwar drainage.
• Secondary saline soils (IGNP-induced): Northern Rajasthan — Sri Ganganagar, Hanumangarh, parts of Bikaner — where heavy canal irrigation without adequate drainage since the 1980s has raised the water table, triggering waterlogging and secondary salt accumulation. Approximately 1.54 lakh hectares of formerly productive land in the IGNP command area are affected.

Characteristics:

• Electrical Conductivity (EC): > 4 dS/m (saline) and/or ESP > 15 (sodic/alkaline)
• pH: > 8.5 in sodic soils (sodium carbonate dominates)
• Whitish salt crust visible on surface
• Plants: Only salt-tolerant species (halophytes) grow naturally — Tamarix, Salicornia, Suaeda

Reclamation measures:

• Gypsum application (CaSO₄) for sodic soils — replaces sodium with calcium ions; Rajasthan produces India's largest gypsum supply (Bikaner/Nagaur — see Topic #88)
• Sub-surface drainage tiles in IGNP command area to lower water table
• Leaching with excess irrigation water to flush salts below root zone
• Salt-tolerant variety cultivation (Karnal Wheat varieties, rice varieties with salt tolerance)

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