Response of Crops to Excess Water (Waterlogging/Flooding)

 General

• Excess water / waterlogging occurs when the soil pores are saturated → oxygen diffusion rate (ODR) < 0.2 μg/cm²/min.
• Crops suffer mainly due to:
  • Oxygen deficiency in root zone (anaerobic condition).
  • Root respiration failure.
  • Toxic substances accumulation (H₂S, CO₂, organic acids, Fe²⁺, Mn²⁺).
  • Reduced N availability (denitrification losses).

Crop Responses

Tolerant Crops (Flood-loving / Submergence tolerant)

• Rice → best adapted (aerenchyma tissue in roots, elongation ability, anaerobic respiration).
• Jute → grows well in waterlogged soils.
• Sugarcane (moderately tolerant, survives temporary waterlogging).
• Certain fodders (para grass, guinea grass).

Moderately Tolerant

• Wheat, Barley, Maize, Sorghum → tolerate short-term waterlogging only.
• Mustard, Potato → moderately affected.

Sensitive Crops

• Pulses (chickpea, lentil, pea, pigeonpea, cowpea).
• Vegetables (onion, tomato, cabbage, cauliflower).
• Fruit crops (citrus, banana, papaya, guava, grape).
• Cotton → very sensitive to prolonged waterlogging.

Physiological & Biochemical Effects

• Roots shift to anaerobic metabolism → accumulation of ethanol, lactic acid → root death.
• Reduced nitrification → more N lost via denitrification.
• Increased Fe²⁺ & Mn²⁺ solubility → toxicity to sensitive crops.
• Waterlogged conditions → favorable for diseases (root rot, wilt).
• Legumes particularly affected due to poor Rhizobium activity under low oxygen.

Soil & Root Zone Changes

• Waterlogging reduces air-filled porosity (<10%) → root suffocation.
• Oxygen Diffusion Rate (ODR) < 0.2 μg/cm²/min → critical for root growth.
• Leads to anaerobic soil conditions → buildup of toxic gases (H₂S, CH₄, CO₂, N₂O).
• Increases solubility of Fe²⁺, Mn²⁺, Al³⁺ → root toxicity.
• Reduces availability of N, S, Zn, Mo.

Exam-Oriented Key Facts

• Rice → most tolerant field crop to waterlogging.
• Jute & Para grass also tolerate waterlogging well.
• Cotton, pulses, vegetables, fruit trees → very sensitive.
• N deficiency is common in waterlogged soils due to denitrification.
• Enzyme activity: Alcohol dehydrogenase increases in roots under waterlogging.
• Long-duration waterlogging = physiological drought (plants cannot uptake water despite abundance).

•  “Which crop is most tolerant to waterlogging?” → Rice.
• “Which enzyme increases in roots under waterlogging?” → Alcohol dehydrogenase.
• “Which nutrients are lost due to waterlogging?” → Mainly Nitrogen (via denitrification).