Response of Crops to Sodicity

General

• Sodic soils (alkali soils):
  • High ESP (Exchangeable Sodium Percentage > 15).
  • High pH (> 8.5–10.5).
  • Poor soil structure (dispersion of clay, hard crust, poor infiltration).
  • Low Ca²⁺, Mg²⁺, Zn, Fe
  • Excess Na⁺ & HCO₃⁻/CO₃²⁻ → toxicity.

• Effect on crops:
  • Poor germination (hard crust + poor aeration).
  • Nutrient deficiencies (Ca, Zn, Fe, B).
  • Stunted growth due to Na⁺ toxicity & osmotic stress.
  • More harmful to dicots (legumes, oilseeds, vegetables) than monocots (rice, wheat).

Crop Response Classification

Tolerant to Sodicity (pH up to 9.5–10)

• Rice (especially under puddled/flooded conditions).
• Barley → most tolerant cereal.
• Bermuda grass, Karnal grass, Para grass → very tolerant fodders.

Moderately Tolerant (pH up to 8.5–9.0); Wheat. Mustard. Cotton. Sorghum, Maize.

• Sensitive (pH < 8.5)
• Pulses: chickpea, pigeon pea, lentil, pea.
• Oilseeds: groundnut, sunflower, soybean, sesame.
• Vegetables: onion, tomato, potato, carrot.
• Fruits: citrus, papaya, banana, guava.

Key Crop-wise Facts

• Rice: most suitable crop for initial sodic soil reclamation (flooding reduces pH & ESP effect).
• Barley: most sodicity-tolerant cereal; grown in severely alkali soils.
• Wheat: moderately tolerant (up to pH 8.5).
• Cotton & Mustard: moderately tolerant, survive in alkali soils.
• Legumes & Oilseeds: highly sensitive, cannot survive above pH 8.2–8.5.
• Fodder grasses: excellent tolerance → used for soil improvement.

Quick Exam Facts

• Sodic soils in India → ~3.7 million ha (U.P., Haryana, Punjab, M.P., Rajasthan).
• ESP threshold for sodicity tolerance:
  • Rice: up to ESP 50.
  • Wheat: up to ESP 30.
  • Barley: up to ESP 60.
  • Pulses/oilseeds: usually ESP < 15.
• Barley > Rice > Wheat > Cotton > Mustard > Pulses (descending tolerance order).
• Rice–Wheat system is most common in sodic soil reclamation areas.
• Fodder grasses not only grow but also help reclaim sodic soils (improve soil structure + add organic matter).

Crop Tolerance Facts

• Most tolerant cereals: Barley > Rice > Wheat.
• Rice → best crop for initial reclamation (flooding reduces Na⁺ effect, improves Ca²⁺ availability).
• Wheat → moderately tolerant (up to ESP 30, pH 8.5).
• Barley → highest tolerance (ESP 60, pH 10).
• Legumes → highly sensitive (nodulation fails, ESP > 15 harmful).
• Oilseeds → sensitive (groundnut, soybean, sunflower fail beyond pH 8.2–8.5).
• Cotton & Mustard → moderately tolerant, grown in sodic belts.
• Fodder grasses (Bermuda grass, Karnal grass, Para grass) → highly tolerant & also improve sodic soils.

Physiological Facts

• High Na⁺ replaces Ca²⁺ in root cell membranes → poor root elongation.
• Sodicity causes dispersion of soil particles → crusting & hardpan, preventing seedling emergence.
• Zn & Fe deficiency common → chlorosis symptoms in crops.
• Rhizobium activity in legumes suppressed → poor nodulation, N-fixation reduced.

Agronomic & Practical Facts

• Rice–Wheat system is the most successful cropping sequence in sodic soil reclamation areas.
• Fodder grasses are pioneer crops used to reclaim sodic soils (add organic matter, improve structure).
• Sodicity reduces water availability to crops despite high soil moisture → termed physiological drought.
• ICAR-CSSRI (Karnal) develops sodicity-tolerant varieties (e.g., CSR series of rice and wheat).

Exam Catchy Points

• Barley = most sodicity tolerant cereal.
• Pulses = most sodicity sensitive group.
• ESP thresholds: Rice 50, Wheat 30, Barley 60, Pulses 15.
• Order of tolerance (general): Barley > Rice > Wheat > Cotton > Mustard > Pulses/Oilseeds.
• Sodic soils are also called Usar, Reh, Kallar soils in India.