Problem soils and soil erosion

Problem soils

Problem soils have some chemical or physical defect that limits crop growth.

• Saline soils: excess soluble salts (chlorides, sulphates of Na, Ca, Mg); electrical conductivity above 4 dS/m, pH below 8.5; white salt crust on the surface. Reclaimed by leaching with good water and providing drainage.
• Alkali (sodic) soils: excess exchangeable sodium (ESP above 15), pH above 8.5; soil is dispersed, hard and poorly permeable; black crust from dissolved organic matter ("black alkali"). Reclaimed with gypsum followed by leaching.
• Saline-alkali soils: both features together.
• Acid soils: pH below 6.5, common in high-rainfall areas; aluminium and iron toxicity, low P availability. Reclaimed with lime.
• Waterlogged soils, with poor aeration.

Salt-tolerant crops such as barley, cotton and sugar beet can be grown on salt-affected land.

Soil erosion

Soil erosion is the detachment and transport of topsoil by water or wind.

• Water erosion stages: splash (raindrop impact), sheet (uniform removal of a thin layer), rill (small channels), gully (deep channels that cannot be smoothed by normal tillage). Ravines of the Chambal valley are an advanced gully form.
• Wind erosion is common in dry, sandy areas such as Rajasthan; movement occurs by saltation, suspension and surface creep.

Control measures

• Agronomic: contour farming, strip cropping, cover crops, mulching, mixed cropping.
• Mechanical: contour bunds, graded bunds, bench terraces on steep slopes, check dams in gullies.
• For wind: shelterbelts and windbreaks of trees, keeping crop residues on the surface.

Soil pollution

Soil pollution is the build-up of harmful substances such as excess pesticides, heavy metals (lead, cadmium, mercury), industrial effluents, plastics and untreated sewage. It reduces soil organisms, enters the food chain and harms health. Controls include judicious agrochemical use, treating effluents and recycling waste.

Key points

• Saline: high salts, pH < 8.5; alkali: high Na, pH > 8.5.
• Gypsum for alkali soils; lime for acid soils.
• Erosion sequence: splash → sheet → rill → gully.
• Terraces for steep slopes; shelterbelts against wind.

Common mistakes

• Using gypsum for saline soils; plain leaching with drainage is the key there.
• Calling sheet erosion the most visible stage; gully is the most visible.