TM 5-803-13/AFM 126-8
is at the right level but the soil needs conditioning, espe-
(2) Pulverizing the surface. The soil surface
cially if it is heavy clay, gypsum should be used. It has
should be harrowed and raked level following tillage to
little effect on pH.
prevent the formation of depressions. A fine-textured
(2) Lime. Lime acts as an agent to increase the
seedbed is important for initial seedling growth. Where
availability of nitrogen, phosphorus and potassium and
large clods are present, a cultivator packer should be used
other chemicals. Lime is commonly used in acid soils to
instead of a harrow to pulverize clods.
raise pH to a less acid level. Common liming materials
(3) Timing. Seedbed preparation should take
are ground limestone, hydrated lime, burned lime and
advantage of favorable soil moisture conditions. Soils
marl. Lime should be applied at a rate and frequency
should not be cultivated when wet, although compacted
determined by the combination of a laboratory soil test
soils should be softened by rain or irrigation prior to
and the recommendation of a local turfgrass specialist. In
tillage.
areas where lime is required, it should be added two or
(4) Grade elevations. The soil surface should be
three months prior to fertilization and mixed in the soil to
true and even and grade elevations undisturbed to ensure
a depth of 6 inches. The best season for application is late
that surface drainage is directed away from buildings and
fall or early winter.
pavements and that there are no depressions where water
(3) Sulfur. The addition of sulfur lowers pH values
will stand. The grade should be rechecked after the
and causes soil to become more acidic. Sulfur is very
seedbed has been prepared. The final grade must be
rarely added except in areas where soils are extremely
approximately 1 inch below adjacent sidewalk and
alkaline.
runway elevations on lawns and airfields to prevent water
(4) Fertilizers. A complete fertilizer is commonly
from accumulating on the pavement and to permit
used for turfgrass establishment, unless a soil test indi-
efficient turf maintenance.
cates otherwise. Fertilizers should be applied to the fin-
(5) Correcting the grade. The seedbed may settle
ished seedbed. Nitrogen fertilizers are divided into
considerably after a heavy rain or irrigation. Such set-
organic and inorganic types. Organic types release
tlement is seldom uniform but tends to occur in spots,
nitrogen slowly, providing for uniform stimulation over
leading to expensive replanting later. This is especially
a long period of time and usually cost more per unit of
objectionable on lawns and recreational areas where a
actual nitrogen. Processed sewage sludge is an example
true final grade is essential. The soil surface should be
of an organic nitrogen source. Inorganic fertilizers are
checked for depressions and fill added to bring the grade
water soluble and are available as dry materials which
to the correct elevation.
require thorough watering into the soil. Inorganic
e. Protection of adjacent areas. Every precaution
fertilizers must be applied in smaller quantities than
should be taken to avoid the disturbance of existing
organic types. The following are inorganic nitrogen fer-
vegetation adjacent to the site. Major grading and the use
tilizers:
of heavy equipment should be restricted to the outer drip
-- Ammonium nitrate.
lines of existing trees. Temporary fencing may also be
-- Ammonium sulfate.
advisable.
-- Ammonium phosphate.
f. Erosion/Nonpoint source pollution control
-- Calcium nitrate.
during site preparation. The implementation of best
-- Nitrate of soda.
management practices (BMPs) can minimize and control
-- Urea.
erosion during preparation. Disturbed areas should be
d. Tillage. Tillage may be desirable for one or more
limited and soil surfaces should be left rough to enhance
of the following reasons: loosening compacted soil,
water infiltration. Stabilization and planting should be
reducing soil erosion, destroying weeds or adding fer-
implemented as soon as possible after a site is disturbed.
tilizers and lime. Deep tillage may also improve soil
If a delay in planting is encountered, temporary mulching
drainage and promote the establishment of a deep root
may be necessary. Soil erosion may be minimized by
system.
applying the following BMPs when applicable.
(1) Initial tillage. An ideal seedbed is made by
(1) The area of land that is exposed to erosion at
tilling the graded soil surface to a depth of 6 to 8 inches
any one time during construction should be limited.
to eliminate areas that may be packed and bard. The
(2) Temporary mulch should be applied on cleared
tilling process also brings objectionable materials such as
areas of the construction site immediately after rough
stones, stumps, large roots and building refuse to the
grading is completed.
surface, where they can be more easily removed. A disk
(3) Sediment basins may be constructed to precipi-
harrow can be used to loosen the soil surface except in
tate silt from storm runoff before it leaves the site.
areas where heavy machinery has packed the soil. A disk
(4) Temporary grade stabilization devices such as
plow or chisel-type tillage tool may be required on
silt fences, diversion berms, water spreaders, sodded
heavily compacted soils.
channels and asphalt flumes may be constructed.
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