Q77: The hydrogen ion toxicity in crops mainly occurs in soil... - Soil Fertility, Plant Nutrition & Fertilizer Management - RPSC Agriculture Research Officer (Agronomy) Screening Test - 2022 | Agrigyan

Direct hydrogen ion (H+) toxicity to plant root cells occurs primarily in extremely acidic soils where pH drops below 4.0 (at pH 4.0-5.5, Al and Mn toxicity predominate).

• < 4: Below pH 4.0, excessive free H+ ions directly damage root membranes, destabilize cell walls, and disrupt cation uptake.
• < 5: Soils with pH between 4 and 5 primarily exhibit aluminium (Al3+) toxicity rather than direct H+ toxicity.
• < 6: Moderately acidic soil, suitable for several crops (like potato, tea), without H+ toxicity.
• < 7: Neutral to slightly acidic soil with no toxicity.