World’s Soil Resources

Prepared by K. Van Oost
Figure 6.1 Spatial variation of soil erosion by water. High rates (>ca. 20 t ha -1 y -1 ) mainly occur on cropland in tropical areas.
The map gives an indication of current erosion rates and does not assess the degradation status of the soils.
The map is derived from Van Oost et al., 2007 using a quantile classification.
The redistribution of soil within fields due to tillage erosion rates may lead to (very) high erosion rates
on convexities (knolls) exceeding 30 tonnes ha -1 yr -1 ; and to deposition rates in hollows and at down slope
field borders exceeding 100 tonnes ha -1 yr -1 . These rates are not directly comparable to wind or water erosion
rates, as soil eroded by tillage will not leave the field. However, tillage erosion may significantly reduce crop
productivity on convexities and near upslope field or terrace borders.
Evidence of past erosion is extensive. This is demonstrated by wind-blown sands of sandstone bedrock,
extensive loess accumulations of silt-sized aeolian sediments, and other formerly aeolian-affected landscapes.
Large areas of sand seas, dune fields and other aeolian features and observations of activity provide further
evidence of past wind erosion (Figure 6.2).
USDA estimates place wind erosion rates at ca. 2.5 tonnes ha -1 yr -1 on average over all cropland of the United
States while the average erosion rate for pastureland is ca. 0.1 tonnes ha -1 yr -1 . There are very few quantitative
assessments of wind erosion rates on arable land outside of the United States.
Status of the World’s Soil Resources | Main Report Global soil status, processes and trends
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