Wind - Agroecology: The Ecology of Sustainable Food Systems - page 91

agitates loose soil particles and eventually lifts and
detaches them from the soil aggregates they may have
been part of. These particles are then transported in
different ways depending on their size and the velocity of
the wind. Small soil particles that bounce across the sur-
face, staying within 30 cm of the surface, are transported
by a process called saltation . Under most conditions, sal-
tation accounts for 50 to 70% of the wind movement of
soil. The impact of saltating particles makes larger parti-
cles roll and slide along the surface, creating soil creep ,
which accounts for 5 to 25% of soil movement. The most
visible form of transport is when particles — the size of
fine sand or smaller, are moved parallel to the surface and
become airborne. Wind turbulence can carry clouds of
these airborne particles several kilometers upward into the
atmosphere and hundreds of kilometers away to eventually
settle or be washed out of the air. Generally, such erosion
is about 15% of the total, but in some cases has been
known to surpass 40%.
When agriculture is practiced in regions of the world
where unprotected soil is subject to wind erosion, great
amounts of topsoil can be lost (Nordstrom and Hotta, 2004).
Desertification in the Sahel of Africa was greatly intensified
in the 1970s by wind erosion of the soil caused by drought,
over-grazing, and intensive cultivation of soils on marginal

lands. The giant clouds of wind-blown soil and dust gener-
ated during the great “dust bowl” of the 1930s in the U.S.
are still one of the most graphic examples of the physical
impact of wind on farming systems through soil loss.
Soil removal from one place and its deposition in
others are dual sides to the wind erosion problem when it
occurs. Reduced soil productivity and crop performance
are the ultimate results unless appropriate precautions are
taken when agriculture is practiced in locations subject to
wind erosion.

T RANSPORT OF O CEAN S ALT

At locations along seacoasts, the physical effect of wind
can be combined with the injurious chemical effect of salt
deposition. When waves break, bubbles and tiny droplets
of salt water are formed and lifted into the air; in the
presence of wind, they can be carried inland and the salt
they contain deposited on leaf surfaces. Wind-blown salt
and salt spray can burn the edges of leaves and even cause
leaf drop.
Damage from wind-transported salt can occur many
kilometers inland from the coast, but the most damaging
effects of salt are seen close to the coastline. Windstorms
without rain cause the most salt damage (Figure 7.4).

FIGURE 7.4 A coastal shrub showing leaf burn and leaf drop caused by wind-deposited ocean salt near Paraiso, Tabasco,
Mexico. Note the accumulated pruning effect at the left on the part of the plant that is directly exposed to the wind.