Vast global reserves of inorganic soil carbon uncovered

Vast global reserves of inorganic soil carbon uncovered
by Simon Mansfield
Sydney, Australia (SPX) Apr 12, 2024

Soil carbon typically denotes the organic matter in soils, known as soil organic carbon (SOC). Yet, there's also an inorganic component to soil carbon, mainly comprising soil inorganic carbon (SIC), which is often calcium carbonate and primarily accumulates in arid regions with poor soil quality. This has led to misconceptions about its significance.

A recent study in Science by Prof. HUANG Yuanyuan and Prof. ZHANG Ganlin from the Institute of Geographic Sciences and Natural Resources Research, along with their team, has quantified the global amount of SIC, disputing previous assumptions.

Their findings reveal an astonishing 2,305 billion tons of SIC in the top two meters of soil globally-over five times the carbon in the world's vegetation. This considerable carbon store plays a crucial role in the global carbon cycle.

"But here's the thing: This huge carbon pool is vulnerable to changes in the environment, especially soil acidification. Acids dissolve calcium carbonate and remove it either as carbon dioxide gas or directly into the water," explained Prof. HUANG.

She highlighted that many areas, particularly in China and India, are witnessing soil acidification due to industrial activities and intensive agriculture. Without intervention and improved soil management, a significant disruption of SIC is anticipated within three decades.

Such disturbances affect the soil's ability to neutralize acidity, regulate nutrients, support plant growth, and stabilize organic carbon. Therefore, SIC is vital not only for carbon storage but also for maintaining ecosystems.

Researchers estimate that about 1.13 billion tons of inorganic carbon are lost from soils to inland waters annually, a significant yet often overlooked aspect of carbon transport between land, atmosphere, freshwater, and oceans.

While the focus has been traditionally on SOC for climate change solutions, this study stresses the importance of inorganic carbon. Programs like the "4 per mille initiative" aim to increase SOC by 0.4% per year, but they must also consider inorganic carbon's role in sustainable soil management and climate mitigation.

By expanding the understanding of soil carbon to include both its organic and inorganic components, the team hopes to enhance soil health, ecosystem services, and climate change mitigation efforts.

Research Report:Size, distribution, and vulnerability of the global soil inorganic carbon