Response of Crops to Salinity

General

1. Saline soils → contain excess soluble salts (mainly NaCl, Na₂SO₄, NaHCO₃).
2. Measured by Electrical Conductivity (ECe) of soil saturation extract.
   • Normal soil: ECe < 2 dS/m
   • Slightly saline: 2–4 dS/m
   • Moderately saline: 4–8 dS/m
   • Highly saline: > 8 dS/m
3. Salinity affects crops due to:
   • Osmotic stress (plants cannot take water).
   • Na⁺ & Cl⁻ ion toxicity.
   • Nutrient imbalance (K⁺, Ca²⁺, Mg²⁺ deficiencies).
4. Salinity problem area in India → ~6.73 million ha (mainly Gujarat, Uttar Pradesh, Haryana, Punjab, Rajasthan, coastal belts).
5. Salinity tolerance threshold = the maximum soil ECe where a crop can grow without yield loss.
6. For every unit increase in ECe above threshold, yield decreases by 5–10% (varies with crop).
7. Salinity affects plants most at germination and seedling stage.

Crop Response Classification (based on tolerance to ECe)

• Sensitive crops (ECe < 3 dS/m); Most legumes (pea, lentil, pigeonpea, chickpea, beans). Fruits & vegetables: onion, carrot, citrus, guava. Cereals: rice (except some tolerant varieties).
• Moderately tolerant (ECe 3–6 dS/m); Cereals: wheat, maize, sorghum. Oilseeds: groundnut, soybean, mustard. Vegetables: tomato, potato.
• Tolerant (ECe 6–10 dS/m); Barley → most tolerant cereal. Cotton → highly tolerant cash crop. Sugar beet → very tolerant root crop. Date palm among fruit crops.
• Highly tolerant (> 10 dS/m); Some fodder grasses (karnal grass, para grass). Certain halophytes (Salicornia, Atriplex).

Crop-wise Key Facts

• Rice – moderately sensitive; some traditional varieties show tolerance (e.g., Pokkali in Kerala).
• Wheat – more tolerant than rice (can tolerate up to 6 dS/m).
• Barley – most salt-tolerant cereal (up to 8–10 dS/m).
• Sugar beet – thrives in saline soils (up to 15–20 dS/m).
• Cotton – highly tolerant cash crop; grows in saline–alkali soils.
• Legumes – generally very sensitive (nodulation suppressed under salinity).
• Oilseeds – mustard & sunflower are more tolerant; groundnut & soybean are sensitive.
• Fruits – date palm, ber, guava show tolerance; citrus, papaya, banana are sensitive.

Mechanisms of Tolerance

• Osmotic adjustment (accumulation of proline, glycine betaine).
• Salt exclusion (roots prevent Na⁺ entry).
• Salt compartmentalization in vacuoles.
• Antioxidant activity to combat salt stress.

Exam-Oriented Quick Facts

• Barley > Cotton > Sugar beet → most tolerant crops.
• Legumes are highly salt-sensitive.
• Rice is sensitive during early stages, but flooding reduces salt effect.
• Pokkali rice (Kerala) and CSR wheat varieties (Canning Salt Resistant) are famous salt-tolerant crops.
• Salinity affects yield more in germination and early seedling stages than later stages.

Crop-Specific Extra Points

• Rice: Some traditional varieties like Pokkali (Kerala), Nona Bokra (West Bengal), and Kalarata (Bangladesh) are naturally salt-tolerant.
• Wheat: Canning Salt Resistant (CSR) varieties developed in India (CSR-10, CSR-23, CSR-36).
• Barley: Tolerates up to 8–10 dS/m → used as indicator crop for saline soils.
• Sugar beet: Extremely tolerant (up to 15–20 dS/m).
• Cotton: Salt-tolerant because of deep roots + osmotic adjustment.

Physiology & Adaptation

• Salinity reduces photosynthesis due to stomatal closure and chlorophyll degradation.
• Na⁺ and Cl⁻ toxicity disturbs K⁺ and Ca²⁺ uptake.
• Plants use compatible solutes (proline, glycine betaine, sugars) for osmotic adjustment.

Agronomic & Breeding Facts

• Seed priming with salts improves germination under saline conditions.
• Use of salt-tolerant varieties + saline irrigation scheduling are major management options.
• Halophytes like Salicornia are being promoted as future saline-soil crops.
• ICAR-CSSRI (Central Soil Salinity Research Institute, Karnal) is the premier institute working on saline soil management & tolerant varieties.