Agriculture Reference
In-Depth Information
while its other edge is buried in the soil. Since solarization requires a minimum period
of 30 days, durable glue is required. In recent years, glues have been developed that are
appropriate for use in continuous mulching.
An alternative system to weld polyethylene sheets together was developed in Israel
(Grinstein & Hetzroni, 1991). Sheet fusing is accomplished with hot air streams,
emitted from a combustion chamber and directed onto the plastic sheets. The machine
is tractor-mounted with a capacity similar to that achieved by the gluing method. The
formulation of the fi lm-additive mixture was found to be of great importance in determin-
ing the strength of the welded seam. Pure polyethylene fi lm is easily welded, but some
additives (e.g. some UV-absorbent ones) were found to interfere with the fusing process,
leading to peeling after only a few days.
An important consideration in large fi eld applications is damage to the mulched fi lm.
Perforation and ruptures in the fi lm increase heating loss from the mulch and decrease
the effective size of the treated area. Once the fi lm is laid, tearing can be caused by
birds, animals and wind. Tears often extend over a large area, thus reducing the effi -
cacy of the solarization treatment. This is a drawback of continuous solarization over soil
fumigation.
10.8.1
Sprayable fi lms
Sprayable polymers offer a feasible and cost-effective alternative to plastic tarps for
SH. The plastic-based polymers are sprayed on the soil surface in the desired quantity
and form a membrane fi lm, which can maintain its integrity in soil and elevate soil
temperatures. Nevertheless, the formed membrane is porous and allows overhead
irrigation. Initial research with these polymers was conducted by Stapleton & Gamliel
(1993), who achieved effective soil heating and a reduction in the viability of
Pythium
propagules. The application, however, was not cost-effective, since a high amount
of polymer was required to achieve a continuous and uniform coating. In Israel, a
sprayable polymer product, 'Ecotex,' was developed together with the technology to
apply it economically on soils for various purposes (Skutelsky
et al.,
2000). Soil coat-
ing using this technology with a black polymer formulation resulted in a membrane
fi lm that could raise soil temperatures to close to solarization levels (Figure 10.2).
Soil heating with sprayable mulch is faster than that with plastic fi lm, but the soil also
cools down to lower temperatures at night. Overall, soil temperatures under spray-
able mulch are lower than those obtained under plastic fi lm. The thickness of the
sprayed coat is critical to obtaining effective heating (Skutelsky
et al.,
2000). SH using
sprayable mulches was effective in controlling Verticillium wilt and potato scab in
potato (Gamliel
et al.,
2001), at a level matching that achieved by solarization using
plastic fi lms. However, there is room for further improvement in the use of sprayable
polymers.
10.9
The use of solar heating for the control of soil-borne pests has expanded over the years
beyond the soil and the pests dwelling in it. The killing properties of heat and humidity
have been used for unusual purposes, some of which are listed below.
Special uses of solarization
