World’s Soil Resources

Figure 6.2 Location of active and fixed aeolian deposits. Source: Thomas and Wiggs, 2008.
6.1.3 | Soil erosion versus soil formation
The accelerated loss of topsoil through erosion from agricultural land was recognized as an important
threat to the world’s soil resource many decades ago. Furthermore, it was feared that soil was, in many areas,
eroding much faster than that it could be replaced through soil formation processes. More recent studies have
confirmed that these early observations were not just perceptions. Estimated rates of soil erosion of arable or
intensively grazed lands have been found to be 100 -1 000 times higher than natural background erosion rates.
These erosion rates are also much higher than known soil formation rates which are typically well below 1
tonnes ha -1 yr -1 with median values of ca. 0.15 tonnes ha -1 yr -1 . The large difference between erosion rates under
conventional agriculture and soil formation rates implies that we are essentially mining the soil and that we
should consider the resource as non-renewable.
The imbalance between erosion rates under conventional agriculture and the rate of soil formation implies
that conventional agriculture on hilly land is not sustainable because the soil resource is mined and will
ultimately become depleted. This has most likely already happened in many areas around the Mediterranean
Sea and in tropical mountain regions. So-called soil loss tolerance levels may help to set objectives for shortterm
action. However, long-term sustainability requires that soil erosion rates on agricultural land are reduced
to near-zero levels.
Figure 6.3 Soil relict in the Jadan basin, Ecuador.
Photo by G. Govers
In this area overgrazing led to excessive erosion and the soil
has been completely stripped from most of the landscape
in less than 200 years, exposing the highly weathered
bedrock below. The person is standing on a small patch of
the B-horizon of the original soil that has been preserved.
Picture credit: Gerard Govers.
Status of the World’s Soil Resources | Main Report Global soil status, processes and trends
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