Soil is the third largest reservoir of carbon, including both organic and inorganic components. Carbon in soil is in the solid form, as opposed to carbon in the gaseous form, such as carbon dioxide (CO2). Soil organic carbon (SOC) is stored in the organic material from decayed plants and animals which is formed when plants convert gaseous CO2 to solid CO2 during photosynthesis. Soil inorganic carbon (SIC) results from the weathering of minerals and reactions of soil minerals with atmospheric CO2. Soil, rich in carbon is essential to soil health and plant growth.
Presently, an estimated 1550 gigatonnes (Gt) of carbon is stored in the Earth’s organic and mineral soil horizons and 900 Gt in the atmosphere. Disruptions to soil, such as deforestation, excessive fertilizer and pesticide use, forest fires, erosion, draining peatlands, and land clearing can deplete soil carbon storage through loss of solid carbon and the conversion of solid carbon into its gaseous state. Globally, human-caused deforestation in the tropics is responsible for an estimated 25% of the CO2 emissions. An estimated 50 to 70% of soil carbon has been lost from the conversion of natural forests to cropland, pastures, and rangelands.
Nature-based solutions (NBS) that incorporate vegetation, such as riparian forests, parks, wetlands, floodplains, boulevard trees, rain gardens, bioswales, green roofs and walls, and gardens, are great ways to maintain and add nutrients such as carbon to soils. With the protection, restoration and creation of natural areas, an estimated 1.85 Gt of soil carbon storage is possible each year.