World’s Soil Resources

Figure 4.10 Global distribution of (a) atmospheric S deposition, (b) soil sensitivity to acidification, (c) atmospheric N deposition, and
(d) soil carbon to nitrogen ratio (soils most sensitive to eutrophication have a high C:N ratio; eutrophication is caused by N). Source:
Vet et al., 2014; Batjes, 2012; FAO, 2007.
Atmospheric deposition data in (a) and (c) were provided by the World Data Centre for Precipitation
Chemistry (http://wdcpc.org, 2014) and are also available in Vet et al. (2014). Data show the ensemble-mean
values from the 21 global chemical transport models used by the Task Force on Hemispheric Transport of Air
Pollution (HTAP) (Dentener et al., 2006). Total wet and dry deposition values are presented for sulphur, oxidized
and reduced nitrogen. Soil data in (b) and (d) were produced using the ISRIC-WISE derived soil properties (ver
1.2) (Batjes, 2012) and the FAO Digital Soil Map of the World.
Trace element deposition
Global trace element emissions and deposition are poorly understood in comparison to our understanding
of emissions of sulphur and nitrogen. Emissions of trace elements are associated with combustion of fossil fuel
(V, Ni, Hg, Se, Sn), traffic (Pb), insecticides (As), steel manufacture (Mn, Cr), and mining and smelting (As, Cu,
Zn, Hg) (Mohammed, Kapri and Goel, 2011). In the United Kingdom, trace element deposition is responsible for
25-85 percent of total trace element inputs to soils (Nicholson et al., 2003). In Europe, the area at risk from Cd,
Hg and Pb deposition in 2000 was 0.34 percent, 77 percent and 42 percent respectively, although emissions are
declining (Hettelingh et al., 2006). In China, 43-85 percent of total As, Cr, Hg, Ni and Pb inputs to agricultural
soils originate from atmospheric deposition (Luo et al., 2009). In bioavailable form these elements have a toxic
effect on soil organisms and plants, influencing the quality and quantity of plant inputs to soils and the rate of
decomposition. Significantly, they can also bioaccumulate in the food chain. Activity of trace elements in soils
will depend on the specific mobility of the element and this will be influenced by pH, Eh and the concentration
of dissolved organic matter with complexing properties (Blaser et al., 2000). Some trace elements will persist
for centuries as they are strongly bound to soil particles. However, they can become bioavailable, as observed
in peatlands following drought-induced acidification, drainage and soil erosion (Tipping et al., 2003; Rothwell
et al., 2005).
Status of the World’s Soil Resources | Main Report Soils and Humans
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