TM 5-830-3/AFM 88-17, Chap. 3
normally equipped with an asphalt spraying mechanism
semiarid regions. The soil should be cohesive enough to
for anchoring the mulch. It can place the mulch and
produce soil clods (lumps of earth with a minimum
asphalt at the same time and at considerable distance
dimension of 1 inch measured in any direction). Strips
from the operating location. Otherwise, anchoring is
should be tilled at 25- to 100-foot intervals at right angles
normally accomplished with either a disk packer or V-
to the prevailing wind. As the strips become smooth
tread rolling wheel packer. Rapid curing (RC) cutbacks
through erosion, new strips should be plowed adjacent to
or rapid setting (RS) asphalt emulsions are normally
the earlier ones. The success of this method depends
used for anchoring, since they are more effective than
upon the formation of a cloddy, rough surface that
the slower curing materials. In an emergency, vegetative
breaks up the sweep of soil particles. Tillage of dry soil
mulch can be anchored by applying a jet of water to bury
typical of desert areas sometimes may be harmful rather
part of the mulch in the soil. About 2,000 gallons of
than beneficial to dust control if a cloddy surface is not
water per acre is needed to provide maximum
produced.
Rough tillage is normally considered a
anchorage. Mulch is undesirable around airports since it
temporary control measure to be followed by permanent
may be ingested into jet engines. Further details on the
vegetative cover, but it sometimes can be sufficient as
recommended uses and methods of applying a wide
the only treatment if traffic is excluded from the area and
variety of mulches are discussed in TM 5-830-2/AFM 88-
the native vegetation is capable of regeneration. Disk-
17, Chapter 2; TM 5-630/AFM 126-2; and Department of
type tillage tools generally should not be used for rough
Agriculture Hand- book No. 346.
tillage as they tend to pulverize the soil too much (i.e.,
(3) Shelter belts. Any barrier of hedges,
soil clods are not formed). However, if long narrow
shrubs, or trees high and dense enough to protect
grooves are created which would channel runoff water,
facilities and unsurfaced soil areas is considered to be a
the tillage should be laid out on horizontal contours to
shelter belt or windbreak. Shelter belts should be placed
prevent water damage.
at right angles to the direction of the prevailing wind.
Several parallel shelter belts may be required and usually
3-3. Surface penetration method
the higher the average wind velocity the closer the
In the surface penetration method, the dust palliative, a
shelter belts should be spaced. While such shelter belts
liquid, is applied directly on the soil surface by spraying
can serve occupied areas, their practical applicability
or sprinkling and allowed to penetrate the surface under
solely for dust control is limited. Trees are slow to
its own accord. Surface penetration applications may be
become established, and additional soil treatment
accomplished with a liquid pressure distributor, by a
between tree belts is usually required.
Finally, in
gravity-flow water distributor, or by hand-held devices.
semiarid regions, where shelter belts or windbreaks are
The spray apparatus should be positioned directly above
most highly valued, trees often cannot be sustained
the area being treated (8-14 inches) to preclude, wind-
without irrigation. Notwithstanding the above limitations,
drift.
Runoff should be avoided (if necessary by
shelter belts can supplement other dust-control
decreasing the application rate or applying the dust
measures by reducing wind velocity. The use of shelter
palliative at one-half the recommended rate and
belts are recommended wherever they do not interfere
repeating the treatment later).
with the intended area activities.
a. Effectiveness.
The effectiveness of the
(4) Rough tillage. Chisels, listers, and turning
surface penetration method depends on the depth of
plows are used to till strips across nontraffic areas that
penetration which is a function of the viscosity of the dust
have become sources of dust. Several strips are placed
in parallel as an emergency measure to control dust in
3-2
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