Wind Erosion of Agricultural Soils and the Carbon Cycle - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 164

cycle is rare. But, nevertheless, some infer-
ences can be drawn based on the current
physical knowledge of aeolian transport.
Soils in the broader sense are a mixture of
grains of different sizes, shapes and proper-
ties. Natural soils have a large variety of
grain sizes of mineral and organic compo-
nents, which are in most cases aggregated,
and the mobilization of the finest particles
of a soil by wind erosion results mainly from
the impacts of sand particles. As shown in
Fig. 13.1 , the wind transports particles in
three main forms: creeping, saltation (mainly
sand) and suspension (mainly dust). Creeping
and saltation include relatively coarse and
heavy particles with relevance for local pro-
cesses, while suspension includes fine and
light particles affecting regional and global
processes (Shao, 2000). The way that wind
erosion further affects the SOC losses has to
be linked closely with the spatial distribu-
tion of the eroded material and its temporal
variability.

not only the highest soil losses but also the
highest SOC concentrations in the eroded
material at the beginning of an erosion event
( Fig. 13.2 ) . The availability of erodible ma-
terial has a limitation due to the enrichment
of coarser fractions or stable aggregates from
deeper and moister layers at the surface
during erosion, lowering the total amounts
and SOC concentrations of the dust follow-
ing erosion events.
The increasing SOC content of the emit-
ted dust can be explained with separation
processes by density differences. Figure 13.3
shows dust on a filter sampled at a height of
3 m. All particles can be regarded to have
the same aerodynamic characteristics, well-
sorted mineral particles of a uniform size
and much larger organic particles (upper left
side), representing a larger volume/mass com-
pared to the original composition. The aero-
dynamic separation therefore causes a relative
increase of SOC in the emitted dust, which
increases in height.

Temporal Variability Spatial Variability

On agricultural land, the susceptibility to
wind erosion is subject to permanent changes.
The highest susceptibility occurs always after
tillage operations that have loosened, crum-
bled and levelled the surface. That causes

Wind erosion processes are subject to a high
spatial variability, at both the small and the
large scale. At the field site, the limited
transport capacity of the wind causes closely
adjacent areas of soil losses and gains.

Suspension: < 70 µm
Distance: km

Saltation: 70- 500 µm
Distance: m

Creep: >500 µm
Distance: cm

Fig. 13.1. Main transport modes of wind erosion depending on particle diameter and transported
distances by wind.