Agriculture Reference
In-Depth Information
10.4.3
Increased growth response (IGR) of plants in solarized soil
Improved plant growth and consequent increases in yield are expected to occur when
soil-borne pests are controlled by any disinfestation method, as has been shown in many
studies. However, less expected is the phenomenon of plant-growth improvement by
disinfestation of soils with no known major pathogens . This was detected in the early
days of soil disinfestation, more than a hundred years ago, and has been observed with all
soil-disinfestation methods, including solarization (Chen & Katan, 1980; Cook & Baker,
1983; Stapleton et al., 1985; Chen et al., 1991; Gamliel & Katan, 1991; and other studies).
Different mechanisms that are not related to pathogen control have been suggested to
explain this IGR in disinfested soils: increased micro- and macro-elements in the soil
solution (Chen & Katan, 1980; Stapleton et al., 1985; Patricio et al., 2006), elimination
of minor pathogens or parasites, destruction of phytotoxic substances in the soil, release
of growth-regulator-like substances, and stimulation of mycorrhizae or other benefi cial
microorganisms (Chen et al., 1991). In another study, the level of soluble organic sub-
stances, that is humic substances, was higher in the solarized soil (Chen et al., 2000).
These soluble substances increased the growth of corn plants as well as populations
of fl uorescent pseudomonads, indicating an additional mechanism for improved plant
growth. In another study (Grunzweig et al., 1993), plant improvement was recorded in
shoots of tomato seedlings 15 days after transplanting, and only 2 weeks later in roots,
and signifi cantly higher levels of chlorophyll and protein contents were detected in plants
from solarized soil as compared to those from control soil. In addition, the degradation
of these compounds, the decrease in net photosynthesis at near-saturation light intensity
and of photochemical yield with ageing, were delayed in plants growing in solarized
soil, as compared to controls. Delayed leaf senescence appeared to be a plant response
contributing to plant improvement in this case. The association between plant-growth
improvement in the solarized soil and microbial activities, such as the stimulation of
benefi cial rhizobacteria and suppression of minor pathogens, has also been reported
(Gamliel & Katan, 1991).
The increases in plant growth in these studies range from a few to several hundred
percent, depending on the soil, the plant, and the parameter used. The effect on yield
components has not always been analyzed.
The defi nition of IGR depends largely on that of a healthy plant. It is now widely accepted
that plant health involves much more than simply disease control. As Browning (1983) states:
'Plant health is far more than the opposite of plant disease as used in plant pathology.'
The IGR has very important economic implications which should be taken into account
when considering the use of solarization. The major diffi culty is that we cannot predict
whether and to what extent a soil will respond with an IGR. Developing predictive methods
for this purpose and developing measures to further enhance the IGR will improve the
economic benefi ts of solarization (and other disinfestation methods).
10.5
Integrated management
Certain control methods, such as fumigation and the use of resistant cultivars, are very
effective and some of them, like the latter, are not harmful to the environment and are
easy to apply. Nevertheless, each method has its limitations, and additionally, cannot be
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