World’s Soil Resources

High soil erosion rates will also have significant negative effects over longer time spans: the loss of topsoil
will result in a reduction in the soil’s capacity to provide rooting space and, more importantly, in the capacity
to store water that can be released to plants. This may reduce soil productivity. However, these changes occur
relatively slowly: the reduction in soil water holding capacity and and/or root space accommodation results
in yield declines of ca. 4 percent per 0.1m of soil lost. Except for areas where erosion rates are very high (e.g.
exceeding 50 tonnes ha -1 yr -1 or ca. 4 mm yr -1 ) this means that effects of erosion on crop productivity will
be relatively small on the decennial or centennial time scale, provided that nutrient losses due to erosion are
compensated. Over longer time spans, however, the effect of these losses becomes very significant.
On the positive side, transported dust affects distant ecosystems, increasing plant productivity by providing
nutrients not provided by the parent soil, as seen in Hawaii (Chadwick et al., 1999) and the Amazon (Mahowald
et al., 2008). Transported dust can also provide chemical constituents that affect soil development, as seen in
the development of terra rossa soils in Bermuda and Spain (Muhs et al., 2010, 2012).
6.1.6 | Soil erosion and the environment
The direct negative effects of soil erosion are not limited to agriculture. The sediment produced by erosion
also pollutes water streams with sediment and nutrients, thereby reducing water quality. In addition,
sediment contributes to siltation in reservoirs and lakes. However, not all sediments trapped in reservoirs
originate from agricultural land. Other processes such as bank erosion, landslides and natural surface erosion
which contribute to reservoir sedimentation are also very important and are often dominant at large scales.
Wind erosion and dust transport have been studied for many years. For example, in 1646, Wendelin first
described purple rain in Brussels that we now recognize as coloured dust transported to Europe from Africa
(Wendelin, 1646 as cited in Stout, Warren and Gill, 2009). Charles Darwin studied dust that fell on the HMS
Beagle in the 1830s and 1840s (Darwin, 1845, 1846) and the dust collected was found to contain viable microbes
even today (Gorbushina et al., 2007).
Wind erosion can originate from natural landscapes and from landscapes affected by anthropogenic
(human-related) activities (Figure 6.4). Aeolian processes impact soil development, mineralogy, soil physical
and biogeochemical properties, and redistribution of soil nutrients, organic materials, and sequestered
contaminants. Wind erosion also affects landscape evolution, plant productivity, human and animal health
(Ravi et al., 2011), atmospheric properties including effects on solar radiation and cloud attributes (Shao et al.,
2011), air quality, and other factors (Field et al., 2010; Ravi et al., 2011). The effects of wind erosion occur at the
field, landscape, regional, and global scales.
Status of the World’s Soil Resources | Main Report Global soil status, processes and trends
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