Agriculture Reference
In-Depth Information
soils in Hawaii by mulching soils with cellophane, apparently controlling
Heterodera
radicicola
. Adams (1971) was probably the fi rst to report the potential of plastic material
for heating soil and controlling pathogens. In 1986, 10 years after the fi rst publication,
nearly 180 publications or reports from 22 countries had already been published on the
topic, indicating a deep interest in new methods of control (Katan
et al.
, 1987). In the
last three decades, since the establishment of SH in its present form, hundreds of studies
on this topic have been published and this approach has been adopted or investigated in
over 60 countries, both developed and developing (Katan, 1981; Stapleton & DeVay,
1986; Katan & DeVay, 1991; Katan, 1996; McGovern & McSorley, 1997; Stapleton
et al.,
1998) (Figure 10.1). Owing to their sheer number, we refer to only some of these studies
in this chapter. Many educational and extension materials for introducing SH in new
areas have also been developed. The studies on SH deal with several major issues, such
as exploring the potential effectiveness of this technique in various regions, seasons and
climatic conditions, mechanisms of disease control and yield increase, and technological
and application issues, among others; some of these issues are discussed herein.
10.2
Principles of soil solarization
Soil solarization is a climate-dependent method which needs to be adapted to the specifi c
region and season in which it is applied. However, there are basic principles which are
common to most uses and are summarized as follows (Katan,
et al.
,
1976; Stapleton &
DeVay, 1986; Katan, 1996):
(a)
Soil mulching should be carried out during periods of high temperature and intense
solar irradiation, and low or no precipitation.
The soil should be kept moist to increase the thermal sensitivity of resting structures
(b)
and to improve heat conduction.
The thinnest polyethylene tarp that can be used (25- to 50-
(c)
m thickness) is
recommended, since it is both cheaper and somewhat more effective than thicker
ones. Because the upper soil layer is heated more intensely than the lower ones, the
mulching period should be suffi ciently long, usually 4 weeks or more, to achieve pest
control at all desired depths. The longer the mulching period, the greater the depth of
effective activity, and the higher the pathogen-killing rates (Katan
et al.,
1976).
Solarization heats the soil through repeated daily cycles. At increasing soil depths,
μ
(d)
maximal temperatures decrease, are reached later in the day, and are maintained for
longer periods of time (Figure 10.2). In solarized plots in which effective disease and
weed control were obtained, typical maximal temperatures were within the range
of 45-50
o
C and 38-45
o
C at depths of 10 and 20 cm, respectively, although higher
temperatures have been recorded in certain regions. The temperatures in the solarized
soil are 5-15
o
C higher than those in comparable non-solarized ones.
The best time for SH, when climatic conditions are the most favorable, can be
(e)
determined experimentally by mulching the soil and measuring the resulting tempera-
tures. Meteorological data from previous years and predictive models (see further on)
further facilitate this task. Monitoring changes in the time span naturally occurring
pathogen populations, or intentionally introduced pathogen inocula, is an additional
approach to determining the effectiveness of SH, and this method can be regarded as
