Agriculture Reference
In-Depth Information
the temperatures can be increased to very high levels, thus leading to control of even the
thermo-tolerant pathogen
Monosporoascus cannonballus
(Pivonia
et al.,
2002).
Over the years, many efforts have been made to move from the clear polyethylene plas-
tic sheets to other polymers and other formulations in order to maximize heat absorbance
under the tarp. The following describes some of the current advances in fi lm formulation
and technology.
10.7.1
Double tarps
The use of a single layer of plastic fi lm is the common application method for SH.
Transparent fi lms allow transition of the solar irradiation, which heats the soil layer adja-
cent to the fi lm. Being thin and with no insulation layer, the heat fl ux also escapes to the
atmosphere through the fi lm. Thus the effi cacy of soil heating is reduced.
10.7.1.1
Two transparent fi lms
One way to increase soil heating is the use of double-layer mulch, which heats the soil
to higher levels than a single one. This was shown by Raymundo & Alcazar (1986),
who achieved an increase of 12.5
o
C at a depth of 10 cm using a double-layer fi lm
compared to a single-layer one (60
o
C versus 47
o
C, respectively). Ben Yephet
et al.
(1987) achieved a similar increase in soil temperature by using double-layer fi lms.
They observed a 98% reduction in the viability of
F.
oxysporum
f. sp.
vasinfectum
after
30 days under the double mulch compared with a 58% reduction under single mulch,
at a depth of 30 cm. Double-layer fi lms form a static air space under and between the
plastic layers. This construction apparently acts as an insulator for heat loss from the
soil to the atmosphere, especially during the night. The use of a double-layer fi lm also
offers opportunities for applying solarization in areas and climatic conditions which
are not favorable for solarization when a single layer is used. In central Italy, in an area
which is climatically marginal for solarization, double-fi lm solarization was very effec-
tive in reducing the viability of
Pythium, Fusarium
and
Rhizoctonia
in a forest nursery
(Annesi & Motta, 1994). This approach was also followed successfully in Australia
with nursery potting mix (Duff & Connelly, 1993). Its one drawback, however, is cost:
a double-layer fi lm is more expensive than one layer of tarp. SH in a closed greenhouse
is another version of the double-layer fi lm which improved disease control (Garibaldi &
Gullino, 1991).
10.7.1.2
Transparent-over-black double fi lm
A different approach to increasing solar heating with a double layer is the use of a
sprayable black polymer as the lower mulch, laid over the soil surface. Stevens
et al.
(1999) reported a 5
o
C increase in soil temperature when applying solarization in strips
in a cloudy climate. Similarly, Arbel
et al.
(2003) achieved an increase in soil tempera-
ture by mulching transparent polyethylene sheet over a layer of sprayable black mulch
(Figure 10.2). In fi eld experiments, they observed that the mortality of resting structures
of
F. oxysporum, S. rolfsii
and
R.
solani
was higher than in the plots which were solar-
ized by a single plastic layer. Consequently, in the solarized plots with double plastic
