Agriculture Reference
In-Depth Information
The influence of high temperatures on weeds, seeds, and pathogens
is complex. It often provides a positive crop growth response in ad-
dition to weed and disease control. Deep rooted, heat tolerant weeds
are usually suppressed, for example, old clover seeds germinated
after solarization. Adding of compost and other soil amendments
may improve control of the more resilient weedy species by increas-
ing microbiological activity in the soil. Solarization also reduces
or eliminates plant pathogens such as
Fusarium chlamydosporum
,
Gibberella fujikuroi
var.
fujikuro, Alternaria alternata,
Verticillium
dahlia
,
Rhizoctonia solani and
root rots (El-Shanawany et al., 2004;
Gamliel and Katan, 1991; Pullman et al., 1981a,b).
12.4
MECHANISM OF SOLARIZATION PRACTICE
Solarization is most effective when done for 4 to 6 weeks during the hot-
test parts of the year. In solarization, the temperature of soil at 0-5 cm in-
creases by about 10°C and is less in the surface layers (5 cm and 10 cm) of
irrigated plots as compared to nonirrigated plots. This is likely due to the
energy required to heat water as indicated in the field condensation on the
lower sheeting surface. As stated previously, the thermal density decline of
soil-borne organisms (plant parasitic nematodes, fungi, and some bacteria)
during solarization depends on soil moisture, temperature and its exposure
time (Stapleton and DeVay, 1995). Although most of the mesophilic mi-
croorganisms in soil have thermal damage thresholds, some thermophilic
and thermo-tolerant microorganisms can survive temperatures achieved
in solarization treatment (Stapleton and DeVay, 1995). Cloud cover, cool
air temperatures, and precipitation events during the treatment period re-
duced solarization efficiency (Chellemi et al., 1997). In addition, other
changes to the physical soil environment also occur during solarization.
An increase in concentration of soluble mineral nutrients concentrations
of ammonium- and nitrate-nitrogen are consistently recorded across a
range of soil types after solarization, improves soil structure and increases
the availability of nitrogen (N) and other essential plant nutrients, while, it
does not influence soil pH, electrical conductivity and available P content
of the treated soil. Soil NH
4
-N levels also not affected by solarization at
any depth (Katan, 1987; Stapleton and DeVay, 1995). The concentrations
of soluble mineral nutrients namely, Ca, K and Mg also increase to some
