Importance of Soil Organic Matter in  Carbon Sequestration

Jan Van Wambeke Jan.VanWambeke@fao.org Pilar Román Pilar.Roman@fao.org

FAO is concerned with the effect of agriculture on climate change, the impact of climate change on agriculture and with the role that agriculture can play in mitigating climate change.

Historically, land-use conversion and soil cultivation have been an important source of greenhouse gases to the atmosphere. It is estimated that they are responsible for about 30% of GHG emissions

The challenges for agricultureThe challenges for agriculture

SUSTAINABILITY FOR FUTURE

GENERATIONS LANDLAND

WATERWATER

GENETIC RESOURCESGENETIC RESOURCES

CLIMATE CHANGE

GROWING WORLD POPULATION

HIGHER AND DIVERSIFIED FOOD CONSUMPTION

Irregular water availability, extreme weather events, higher normal temperatures

3

Source: CGIAR

Carbon sequestration: the process of removing carbon from the atmosphere or preventing its release altogether by guarding it in a reservoir.

Agricultural soils are among the planet’s largest reservoirs of carbon. It is estimated that soils can sequester around 20 Pg C in 25 years, more than 10 % of the anthropogenic emissions

Carbon storage in soils is the balance between the input of dead plant material (leaf and root litter) and losses from decomposition and mineralization processes (heterotrophic respiration).

Under aerobic conditions, most of the carbon entering the soil is labile, and therefore respired back to the atmosphere through the process known as soil respiration or soil CO2 efflux.

The quantity of carbon stored in soils is highly significant; soils contain about 3 times more carbon than vegetation and twice as much as that which is present in the atmosphere

Source: FAO

Source: FAO

“The importance of these activities is that any action taken to sequester carbon in biomass and soils will generally increase the organic matter content of soils, which in turn will have a positive impact on environmental, agricultural and biodiversity aspects of ecosystems. The consequences of an increase in soil carbon storage can include increases in soil fertility, land productivity for food production and security, and prevention of land degradation”

Soil carbon sequestration presents both advantages and disadvantages as a means of mitigating climate change.

•Advantages– Relatively low-cost – It can be readily implemented– it provides multiple associated benefits as the resultant increase in root

biomass and soil organic matter enhances water and nutrient retention, availability and plant uptake and hence land productivity

•Disadvantages– It is reversible, changes in agricultural management practices or disasters as

fires, droughts or pests can accelerate or reverse the degree of sequestration in a relatively short time frame.

FAO material on Carbon Sequestration