Environmental Engineering Reference
In-Depth Information
It harbours potentially destructive diseases and turf insects, limits
root penetration into the soil and, in some cases, causes hydropho-
bicity. Heavily thatched turfs may also affect games in which the
bouncing response of
the ball
is critical
to the performance of
the players.
Any factor that influences the rate of production and/or decompos-
ition of organic matter influences production of thatch. As the balance
between accumulation and decomposition is swayed one way or the
other, the thickness of the thatch layer increases or decreases. Major
influences include grass species, fertilization (especially nitrogen), soil
pH, mowing height, pesticide applications, soil type and in some turf-
grasses means of clipping disposal.
Thatch is broken down primarily by the activity of soil-borne
microbes and earthworms. Any factor that increases their activity accel-
erates thatch decomposition. Therefore, maintaining an appropriate pH,
good soil aeration and adequate soil moisture reduce thatch accumula-
tion. On the other hand, increased nitrogen fertilization usually speeds
up turf-grass growth and results in faster thatch accumulation. Neutral
soil pH and some natural organic fertilizers improve composition of the
microbial community, therefore reduce thatch build up. Some pesticides
increase thatch levels by adversely affecting the composition and activity
of thatch-decomposing microbes. Mulching mowers, which finely chop
grass blades, promote decomposition and therefore contribute less to
thatch than do other types of mowers. In some species, like zoysia
grass, the clippings contain high concentrations of silica, which protect
the leaves from fast decomposition and therefore add to the thatch layer.
Soil type may also affect thatch formation. Turf being grown on heavy
soil usually develops thatch faster than the same turf grown on better-
aerated sandy soil.
When thickness of the thatch layer exceeds 1.5 cm, it can become a
problem and should be reduced. The thatch layer should be examined in
several cores removed with a soil sampler or even a pocket knife. If its
thickness significantly exceeds 1.5 cm, dethatching is recommended. One
of the most common methods of thatch control is vertical mowing,
sometimes called 'verticutting'. The blades of the vertical mower (also
called a dethatcher) cut vertically into the turf canopy, severing lateral
stems and removing thatch that develops on the surface of the soil
(Fig. 8.6). Thatch is brought to the surface of the turf, from which it
must be raked and removed. The tearing action of the blades can ser-
iously disrupt the surface, so after vertical mowing, turf requires a period
of recuperation, usually 2-3 weeks. Some turf areas never need dethatch-
ing, but others need it quite frequently. Golf greens in the tropics are
dethatched every several weeks but lightly; recreational areas or home
