Context

A recent study highlighted that soil acidification could erode soil inorganic carbon, a stable carbon pool, which could affect the health of soil and its ability to regulate nutrient levels.

• Acidic Soil: Over 30% of cultivable land in India is said to carry acidic soil, impacting plant growth.
• Loss of SIC: Industrial activities and intensive farming are causing soil acidification in India, potentially causing a loss of 3.3 billion tonnes of soil inorganic carbon (SIC) from the upper 0.3 meters of soil over the next three decades.

About Soil Acidification

• Soil acidification: It refers to the process by which soil becomes more acidic, typically due to natural factors like rainfall and biological processes, as well as human activities such as industrial emissions and the extensive use of nitrogen-based fertilizers.
  • This process leads to a decrease in soil pH, which can adversely affect plant growth, nutrient availability, and soil biology. 
• Geographical Spread of Soil Acidification in India:
  • Soil acidification is already a concern in the country, affecting about 48 million hectares (mha) out of 142 mha of arable land.
  • Acidic soils in India are widespread in the humid southwestern, northeastern and Himalayan regions. The northeastern region, in particular, has recorded acidity in approximately 95 per cent of the soils.

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Impact of Soil Acidification

• Affects crop growth: This is worrying because acidic soils affect crop growth and productivity by reducing the availability of plant nutrients. 
  • It also predisposes plants to other biotic and abiotic stress factors.
• Depletion of Soil Inorganic Carbon (SIC): Soil acidification leads to SIC depletion as most of the SIC (by weight) is carbonate. 
  • Acidic soil dissolves solid carbonate and removes it either as carbon dioxide gas or releases them directly into the water.
• Affects Nutrient levels and Carbon storage capacity: Soil Acidification not only reduces SIC but also affects nutrient levels and carbon storage capacity, crucial for plant growth and carbon sequestration.
• Increase Solubility of Toxic Elements: Over time, acidification can increase the solubility of potentially toxic elements like aluminum.

About Soil Carbon

• Carbon in Soil: It can be stored in the form of Soil Inorganic Carbon or Soil Organic Carbon (SOC). 
• Soil Inorganic Carbon: It  includes mineral forms of carbon like calcium carbonate produced by weathering parent material in soil or from the reaction of soil minerals with atmospheric carbon dioxide.
  • SIC is important for soil health, ecosystem services and functions along with carbon sequestration.

• Soil Organic Carbon: It plays a role in nutrient cycling and is the main component of soil organic matter such as plant and animal waste, microbes and microbial byproducts.
• Together, soils store more than thrice the quantity of carbon in vegetation or double the quantity of carbon in the atmosphere.
• India is likely to be most affected by SIC losses due to relatively large stocks of SIC and the magnitude of soil acidification associated with nitrogen additions.
• Climate Change causing SIC loss: Globally, future global warming and soil pH changes will deplete SIC in the top 0.3 m of soil by 1.35, 3.45 and 5.83 gigatonnes of carbon (GtC) under different scenarios, where temperatures could likely reach around 1.8°C, 2.7°C and 4.4°C warming by 2100, respectively.
• Loss of SIC to inland waters: Further, every year, approximately 1.13 billion tonnes of inorganic carbon are lost from soils to inland waters. 

Way Forward

There is a need for a comprehensive soil management strategy to address soil acidification and depletion of SIC and SOC from the soil.

• Soil pH Monitoring and Management: Soil Health Cards provide the status of nutrients and pH of soil which can be used for regular monitoring of soil quality. Furthermore, soil can be treated with calcium carbonate to neutralize acidity and raise the pH.
• Optimized Fertilizer Use: Reduce dependency on chemical fertilizers by integrating organic fertilizers such as compost and manure.
• Crop Rotation and Diverse Cropping: Rotating crops and including legumes or deep-rooted plants in rotations can enhance soil structure, increase biodiversity, and improve nutrient cycling, which helps maintain a healthy pH balance.
• Controlled Water Management: Implement water management practices that optimize moisture levels without leading to waterlogging or excessive dryness, which can exacerbate acidification.
• Soil Organic Matter Management: Promote conservation tillage and cover cropping practices among farmers to build up organic matter and improve soil structure.

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