Soil carbon

[3] Biotic factors include photosynthetic assimilation of fixed carbon, decomposition of biomass, and the activities of diverse communities of soil organisms.

[5] Soil carbon distribution and accumulation arises from complex and dynamic processes influenced by biotic, abiotic, and anthropogenic factors.

[6] Although exact quantities are difficult to measure, soil carbon has been lost through land use changes, deforestation, and agricultural practices.

[9] Although exact quantities are difficult to measure, human activities have caused substantial losses of soil organic carbon.

[12][13] Climate change is a leading factor in soil formation as well as in its development of chemical and physical properties.

Plant materials, with cell walls high in cellulose and lignin, are decomposed and the not-respired carbon is retained as humus.

[23] 5–20% of the total plant carbon fixed during photosynthesis is supplied as root exudates in support of rhizospheric mutualistic biota.

Specific carbon related benchmarks used to evaluate soil health include CO2 release, humus levels, and microbial metabolic activity.

Although exact quantities are difficult to measure, human activities have caused massive losses of soil organic carbon.

In the Netherlands, East Anglia, Florida, and the California Delta, subsidence of peat lands from oxidation has been severe as a result of tillage and drainage.

Natural variations in soil carbon occur as a result of climate, organisms, parent material, time, and relief.

[34] The greatest contemporary influence has been that of humans; for example, carbon in Australian agricultural soils may historically have been twice the present range that is typically 1.6–4.6%.

[35] It has long been encouraged that farmers adjust practices to maintain or increase the organic component in the soil.

In the article "Estimating soil organic carbon in Europe based on data collected through a European network" (Ecological Indicators 24,[36] pp.

The LUCAS soil organic carbon data are measured surveyed points and the aggregated results[37] at regional level show important findings.

This modelling framework has been updated by integrating the soil erosion component to estimate the lateral carbon fluxes.

[39] Currently, the EU-ORCaSA [40] project is developing a multi-ecosystem framework for measuring, reporting and verification of soil organic carbon changes to support policy making.

Anthropogenic activities such as deforestation cause releases of carbon from this pool, which may significantly increase the concentration of greenhouse gas (GHG) in the atmosphere.

[45] Deforestation, forest degradation, and changes in land management practices can cause releases of carbon from soil to the atmosphere.

West Africa has experienced significant loss of forest that contains high levels of soil organic carbon.

[48][49] This is mostly due to expansion of small scale, non-mechanized agriculture using burning as a form of land clearance [50]

Impact of elevated CO 2 on soil carbon reserves
Global Carbon Cycle
Soil carbon cycle through the microbial loop
Carbon dioxide in the atmosphere is fixed by plants (or autotrophic microorganisms) and added to soil through processes such as (1) root exudation of low-molecular weight simple carbon compounds, or deposition of leaf and root litter leading to accumulation of complex plant polysaccharides. (2) Through these processes, carbon is made bioavailable to the microbial metabolic "factory" and subsequently is either (3) respired to the atmosphere or (4) enters the stable carbon pool as microbial necromass. The exact balance of carbon efflux versus persistence is a function of several factors, including aboveground plant community composition and root exudate profiles, environmental variables, and collective microbial phenotypes (i.e., the metaphenome). [ 17 ] [ 18 ]
A portable soil respiration system measuring soil CO 2 flux