World’s Soil Resources

Our understanding of the rates for the three erosion agents (wind, water and tillage) is uneven. Erosion
rates due to water erosion remain very high (> ca. 20 tonnes ha -1 yr -1 ) in cropland in many agricultural regions
(Figure 7.2); essentially any cropped area with hilly land and sufficient precipitation is at risk. No reliable global
estimates for current wind erosion rates exist, and the estimates of the human contribution to current dust
emissions range from only 8 percent in North Africa to approximately 75 percent in Australia (see also Section
6.1 above). Tillage erosion primarily results in in-field redistribution of soil, and decreases the productivity of
soils in convex slope elements and near-upslope field or terrace borders. Global-scale summaries also require
consideration of the fate of eroded soil – in some regions deposition of eroded soil in river floodplains and
deltas creates areas of very high and enduring fertility.
The effect of soil erosion on individual soil properties related to crop production is well documented, but
the aggregate effect of soil loss on crop yields themselves is less firmly established. The four integrative
studies summarized in Table 7.1 are based on data sources which range from experimental plot data to reinterpretation
of GLASOD data. The range of estimates of annual crop loss due to erosion ranges from 0.1
percent to 0.4 percent, with two studies estimating 0.3 percent yield reduction.
If the median value of 0.3 percent annual crop loss is valid for the period from 2015 to 2050, a total reduction
of 10.25 percent could be projected to 2050 (assuming no other changes such as the adoption of additional
conservation measures by farmers). Foley et al. (2011) cite a value of 1.53 billion ha for cropland globally; the
loss of 10.25 percent of yield due to erosion would be equivalent to the removal of 150 million ha from crop
production or 4.5 million ha per year.
Figure 7.5 Direct impacts of soil threats on specific soil functions of relevance to plant production.
Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services
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