Soil Acidification in India: A Silent Threat to Soil Health and Carbon Reserves

• Soil health forms the foundation of agricultural sustainability, food security, and ecological balance. 
• However, a growing but often overlooked concern is soil acidification—a process where the pH of the soil declines over time, rendering it increasingly acidic and less fertile. 
• A recent study has raised alarm bells by estimating that India could lose nearly 3.3 billion tonnes of essential soil carbon due to acidification, a figure that holds serious implications for national climate goals and food productivity.

What is Soil Acidification?

• Soil acidification is the gradual decline in the pH of soil, making it more acidic. 
• While some soils are naturally acidic, anthropogenic activities have significantly accelerated this process across large parts of India.

Major Causes of Soil Acidification

• Ammonium-based Fertilizers: Excessive and prolonged use of urea and other ammonium fertilizers leads to nitrification, a microbial process that releases hydrogen ions, thus lowering soil pH.
• Decomposition of Organic Matter: The breakdown of plant residues and compost releases organic acids, further contributing to soil acidification.
• Root Respiration: During active growth phases, plant roots release carbon dioxide into the soil, which reacts with water to form carbonic acid—a weak acid that lowers pH over time.
• Leaching in High Rainfall Areas: In regions with heavy rainfall, important base cations like calcium, magnesium, and potassium get leached away, leaving behind more acidic ions like hydrogen and aluminium.

Consequences of Soil Acidification

• Soil acidification severely impacts both soil health and plant productivity:
  • Loss of Soil Inorganic Carbon (SIC): Acidification disrupts carbonate stability, leading to massive losses of inorganic carbon—a vital component for soil buffering capacity.
  • Aluminium Toxicity: Low pH increases the solubility of aluminium, which becomes toxic to plant roots and restricts nutrient uptake.
  • Decline in Microbial Activity: Beneficial microbes cannot survive in highly acidic conditions, disturbing soil biodiversity and nutrient cycling.
  • Reduced Nutrient Availability: Nutrients such as phosphorus, calcium, and magnesium become less available, leading to stunted crop growth.
  • Increase in Pathogenic Fungi: Acidic conditions can promote harmful fungi, further affecting plant health.

Management and Reversal of Soil Acidification

• Combating soil acidification requires a multi-pronged strategy:

Liming

• Application of lime (calcium carbonate), dolomite (calcium magnesium carbonate), or gypsum can neutralize soil acidity and restore pH balance.

Use of Industrial By-products

• Innovative recycling of press mud (from the sugarcane industry), basic slag (from steel plants), and flue dust (from cement factories) can be effective in treating acidic soils while also reducing industrial waste.

Acid-Tolerant Crops

• Certain crops such as sugarcane and bananas are more tolerant of low pH conditions and can be cultivated in acid-prone areas as a short-term adaptation strategy.

Balanced Fertilization

• Avoiding overuse of ammonium fertilizers and ensuring balanced use of nitrogen, phosphorus, and potassium can prevent further acidification.

Regional Context in India

• Soil acidification is particularly prevalent in:
  • North-eastern India (due to heavy rainfall and shifting cultivation),
  • Western Ghats and Coastal Karnataka,
  • Parts of Jharkhand, Chhattisgarh, and Odisha.
  • These regions are characterized by high organic matter decomposition, intense leaching, and poor liming practices.

Link with Climate Change

• Soil acidification undermines the soil’s role as a carbon sink. With India being a signatory to the Paris Agreement, the loss of 3.3 billion tonnes of soil carbon threatens to derail national efforts in carbon sequestration and emission reduction.
• Moreover, degraded soils lead to lower agricultural yields, potentially affecting food security for millions, especially small and marginal farmers who lack access to soil amendments.

Way Forward: Policy and Farmer Awareness

• Soil Health Card Scheme must be updated to include pH correction recommendations and local liming practices.
• Awareness campaigns in regional languages should educate farmers on the dangers of acidification and the importance of soil pH management.
• Subsidies and incentives for liming agents and industrial by-products can encourage adoption at the grassroots level.
• Scientific research must focus on crop-breeding for acid-tolerant varieties and innovative soil management techniques.