World’s Soil Resources

affect the soil C balance through the removal and/or deposition of the C contained in the transported soil.
Leaching of dissolved organic (DOC) and dissolved inorganic carbon (DIC) through the soil profile and out into
groundwater and surface water represents an additional loss pathway that can be significant in some soils.
Maintaining and increasing SOC stocks through improved land use and management practices can help
to counteract increasing atmospheric CO 2
concentrations (Paustian et al., 1998, Smith et al., 2007; Whitmore,
Kirk and Rawlins, 2014). Increasing soil C content also improves other chemical and physical soil properties,
such as nutrient storage, water holding capacity, aggregation and sorption of organic and/or inorganic
pollutants (Kibblewhite, Ritz and Swift, 2008). Carbon sequestration in soils may therefore be a cost-effective
and environmentally friendly way to store C. It can also enhance other ecosystem services derived from soil,
such as agricultural production, clean water supply, and biodiversity by increasing SOM content and thereby
improving soil quality (Lal, 2004).
O site OM
additions
Plant
photosynthesis
CO 2
CO 2
Plant
respiration
Harvest
Soil deposition
Litter
fall
SOM
turnover and
stabilization
Decomposition &
microbial
respiration
CO 2
Soil erosion
Drawing by A. Swan and K. Paustian
DOC & DIC
Figure 2.1 Overview of ecosystem processes involved in determining the soil C balance.
2.1.1 | Quantitative amounts of organic C stored in soil
Organic C stocks in the world’s soils have been estimated to comprise 1 500 Pg of C down to 1 m depth and
2 500 Pg down to 2 m (Batjes, 1996). Recent studies, based on newer estimates for the C stored in boreal
soils under permafrost conditions, suggest that soil C storage may be even greater, accounting for as much as
2000 Pg to 1 m depth (Tarnocai et al., 2009). Although the highest C concentrations are found in the top 30
cm of soil, the major proportion of total C stock in many soils is present below 30 cm depth (Batjes, 1996). In
the northern circumpolar permafrost region, at least 61 percent of the total soil C is stored below 30 cm depth
(Tarnocai et al., 2009).
Status of the World’s Soil Resources | Main Report The role of soils in ecosystem processes
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