Since carbon forms the ‘backbone’ biochemical structure of all living things, it is intimately associated with the various processes involving air, water, soil, and the sun. One vitally essential process that starts the carbon cycle is photosynthesis, which embodies all
four of these elements in a magical moment that occurs every day all over the Earth – photonic energy from the sun is captured within chloroplasts of green plants that encase water imbibed from the soil in a conglomeration of cells structurally arranged to allow oxygen and CO2
to permeate its boundaries to create a chemical cocktail of carbohydrates that eventually forms the web of life for animals and decaying organisms.
Carbohydrates fuel plant growth and their utilization releases CO2 and water vapor back to the atmosphere. A key carbon
pathway in the global carbon cycle is the transfer of carbon resources from living plants to soil organisms through decomposition, which eventually enriches soil organic carbon pool.
Importance of soil
Soil is as vital to human survival as air, water and the sun are; its protection and enrichment with organic carbon are needed for the future
sustainability of our planet.
Many global issues are intricately linked to soil properties and processes, including food availability, fresh water availability, need for
external nutrients, production of bio-based energy, climate change, biodiversity and ecosystem resilience, waste recycling, and addressing
local issues within a global context.
What is soil carbon?
Soil carbon is composed of inorganic carbonates and organic matter – living roots, insects and microorganisms as well as dead, dying and
partially decayed organic matter.
Soil organic matter is composed of 50–58% carbon.
Soil organic carbon is a critical driver for improving physical, chemical and biological processes and properties of soil quality; also, it
controls landscape and global level processes of hydrologic function, nutrient cycling, and greenhouse gas emission and mitigation.
Soil carbon in a global context
Soil carbon is the largest pool of global terrestrial carbon – 1600 Pg (1015 g) of carbon stored in soil to a depth of 1 m as organic matter and
700 Pg of carbon stored in soil as carbonate minerals.
With approximately 4 Pg of additional carbon accumulating in the atmospheric pool (~800 Pg) each year, complete restoration of the
estimated 20% loss of soil organic carbon that occurred during the past 200 years of cultivation could fully counteract the current rate of
CO2 accumulation in the atmosphere during the next century.
How does soil carbon aect ecosystem properties & services?
Soil organic carbon is a key indicator of soil quality, because of its benecial eects on physical characteristics (e.g., color, solubility,
water retention and soil structure), chemical qualities (e.g., cation exchange capacity, buering, pH, chelation of metals and interactions
with xenobiotics), and biological attributes (e.g., reservoir of metabolic energy, source of macronutrients, enzymatic activities and
ecosystem resilience).
Soil organic carbon accumulates predominately in the upper horizon of soil, which is important for water inltration, nutrient cycling and
protection of o-site water quality.
Can management increase the stock of soil organic carbon?
Loss of soil organic carbon has occurred in the past due to deforestation and cultivation of native ecosystems; great potential exists to
replenish soil organic carbon, because of this historic loss.
Adoption of conservation agricultural systems will sequester soil organic carbon at a generally observed rate of 0.25–1.0 Mg C ha-1 year-1.
Conservation agricultural management may include conservation tillage, diverse crop rotations, cover cropping, manure application, and
integration of perennial forages and animal grazing with cropping.
Who will benet from increasing soil organic carbon?
Increasing soil organic carbon rewards farmers and landowners with better tilth, higher nutrient-supplying capacity, improved resilience to
perturbations and weather extremes, and abundant biological diversity to support vigorous plants and sustained ecosystem services.
Society benets from cleaner water, cleaner air, and low-cost and healthy supply of food products.
Barriers to adoption of conservation agricultural practices
Adoption of various conservation agricultural management approaches is a human choice to build a positive relationship with Nature;
allowing us to sustain our food production systems and improve the environment into the future.
Carbon trading may eventually become a marketing tool that helps broaden society’s appreciation for the inherent value of soil carbon as
a fundamental basis for sustainability
