Environmental Engineering Reference
In-Depth Information
In tropical climates, renovation by seeding is performed only occa-
sionally. The process is quite difficult and usually costs more than vege-
tative renovation. Nevertheless, if seeding is chosen, the area being
renovated should be mowed as low as possible, preferably to a height
of less than 1.0 cm. Reducing the height of the previous turf ensures
adequate light for the emerging seedlings (the old turf should not be
mowed before application of glyphosate, because this herbicide is taken
up by leaves, and mowing would reduce its effectiveness). The next step
depends on the amount of thatch that has accumulated in the area (see
Chapter 8, this volume). The seeds must germinate in contact with the
underlying soil. Seeds that germinate in the thatch are unlikely to sur-
vive. Thatch layers more than 3-cm thick should be removed with a sod
cutter and discarded. For thinner thatch layers, a vertical mower
(dethatcher) should be used to slice through the sod to the underlying
soil in two directions, and the excess thatch should then be raked from
the surface. Core aerification may also be advisable if the soil is com-
pacted. Once the thatch has been removed, the seed can be spread on the
area being renovated. Because some seed will germinate in the debris
above the soil surface and be lost, the seeding rate appropriate for bare
soil should be increased by at least 25%. The seed should be worked into
the seedbed as much as possible; an additional pass with the vertical
mower will bring the seed into better contact with the underlying soil.
A starter fertilizer should be applied to the surface as a final step at the
same rate recommended for normal seeding. The area should be irrigated
as would any other newly seeded area. The debris from the old turf cover
will serve as mulch and may reduce the need for irrigation. Post-germin-
ation care should be the same as that for any other seeded area.
If the new turf in the renovated area will be established vegetatively,
several other approaches can be used. If sodding is chosen, a thin layer of
soil should be distributed over the area, and sod should be laid down in
the same manner as for sodding on bare soil. The purpose of the soil layer
is to provide continuity between the sod and the underlying soil. Without
this step, sod placed on a thick mat of dead grass will suffer from
desiccation. The added soil also provides a better environment for
microbial activity and therefore speeds up decay of the old turf.
If plugging is chosen, the turf area should be mowed the day after
application of glyphosate. Mowing should be at the usual height, and the
clippings should be collected and removed. Mowing should be as accur-
ate and visually appealing as possible because, even though the old grass
is dead, it will serve as temporary turf for several months while the plugs
spread. Removal of clippings is important because glyphosate speeds up
maturation of weed seeds; if it is left on the surface, weeds may germin-
ate and contaminate future turf area. When the grass turns yellow (usu-
ally within a week) but some weeds still remain green, a second
