According to the study Published journal “Science” soil acidification might lead to loss of 3.3 billion tonnes of soil inorganic carbon (SIC) from the top 0.3 metres of its soil over the next 30 years in India.

Background

• Over 30 per cent of cultivable land in India is acidic soil, impacting plant growth. Soil acidification is already a concern in the country, affecting about 48 million hectares (mha) out of 142 mha of arable land.
• Carbon in soil can be stored in the form of soil inorganic carbon (SIC)  or soil organic carbon (SOC). The former 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.
• The latter, which plays a role in nutrient cycling, is the main component of soil organic matter such as plant and animal waste, microbes and microbial byproducts.
• Soils store more than thrice the quantity of carbon in vegetation or double the quantity of carbon in the atmosphere.

Major Highlights of the Study

• India is likely to be most affected by soil inorganic carbon (SIC) losses due to relatively large stocks of SIC and the magnitude of soil acidification associated with nitrogen additions.
• Soil acidification creates an environment ripe for SIC depletion. Most of the soil inorganic carbon (by weight) is carbonate.
• Low pH levels (acidic soils) dissolves solid carbonate and removes it either as carbon dioxide gas or releases them directly into the water.
• 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.
• The large SIC pool revealed through this study and its high vulnerability to acidification-induced losses may pose a risk to limiting net carbon dioxide emissions to the atmosphere in line with the Paris Agreement goals.
• Every year approximately 1.13 billion tonnes of inorganic carbon are lost from soils to inland waters. This loss could have overlooked implications for carbon transport between the land, atmosphere, freshwater and ocean, the researchers warned.

Soil Acidity

• Soil acidity is a condition where the soil pH is lower than neutral (less than 7). Soil pH is a measure of the concentration of hydrogen (H+) ions.

Causes of Soil acidity

• Leaching: Excessive rainfall or irrigation can wash out nutrients like potassium, magnesium, and calcium. Laterite soil is generally acidic due to leaching caused by heavy rainfall.
• Rainy areas: Soil in rainy areas tends to be more acidic than soil in dryer areas.
• Chemical fertilizers: The addition of nitrogen and sulfur fertilizers can lower soil pH over time.

Impact on Soil

• Decreasing the availability of essential nutrients
• Increasing the impact of toxic elements
• Decreasing plant production and water use
• Affecting essential soil biological functions like nitrogen fixation
• Making soil more vulnerable to soil structure decline and erosion