Soils

This section covers soil profile layers (Horizons A, B, and C) and the basic factors of soil formation. UPSC often tests structural and functional differences between horizons. Horizon A is the topmost zone where organic matter is incorporated; Horizon B is a transition zone containing mineral and organic matter; Horizon C consists of loose parent material. Bedrock lies below this. Note that parent material dictates chemical properties and mineral structure, while climate determines weathering rates. Skip overly simplistic definitions but do not skip the sequence of layers or the interplay of factors.

Focuses on the ICAR classification of Indian soils based on their character and USDA soil taxonomy. Crucial data to memorize is Table 6.1 (Soil Orders in India): Inceptisols are the most abundant order (39.74%), followed by Entisols (28.08%) and Alfisols (13.55%). Vertisols (black soils) account for only 8.46%. A classic UPSC trap is to state that Vertisols are the most dominant soil order in India, or to confuse the properties of Inceptisols with Aridisols. Memorize the descending order of these taxonomy classes.

The most high-yield section of this chapter. It details eight soil types: Alluvial, Black, Red & Yellow, Laterite, Arid, Saline, Peaty, and Forest. Key facts: Alluvial soils are rich in potash but poor in phosphorus; Bhangar is older alluvium with kankar (calcareous) deposits, while Khadar is newer silt. Black soil (Regur) is rich in iron, lime, calcium, potassium, magnesium, but poor in nitrogen, phosphorus, and organic matter; it is self-ploughing and highly moisture-retentive. Red soils develop on crystalline igneous rocks and look yellow when hydrated. Laterite soils are heavily leached, rich in iron and aluminium oxides, but poor in nitrogen, calcium, and phosphate. Saline soils (Usara) occur in dry climates and are induced by capillary action in canal-irrigated zones. Peaty soils are acidic and have high organic content (40-50%).

Examines structural, physical, and chemical decline of soil quality. Focus on water and wind erosion. Sheet erosion is common on steep slopes and goes unnoticed but is highly destructive as it removes the fertile topsoil layer. Gully erosion cuts deep ravines, forming badland topography typical of the Chambal basin. Anthropogenic soil degradation is dominated by salinity issues in Punjab, Haryana, and western UP due to excessive canal irrigation and flooding methods. Traps include confusing sheet erosion with rill erosion, and assuming wind erosion is confined strictly to Rajasthan deserts.

Focuses on engineering and agronomic solutions to combat soil loss. Key methods include contour bunding, terrace farming, strip cropping, shelterbelts, and agro-forestry. The Central Soil Conservation Board (established in 1953) is a critical institutional detail. Note the specific regional applications: contour bunding and terracing are used in hilly terrains (Himalayas and Western Ghats), while shelterbelts and sand dune stabilization using windbreaks are critical in western Rajasthan. Avoid generalist assumptions that any technique works universally; UPSC questions test specific geographical pairings.