Soil solarization is a non-chemical
environmentally friendly
Environment friendly processes, or environmental-friendly processes (also referred to as eco-friendly, nature-friendly, and green), are sustainability and marketing terms referring to goods and services, laws, guidelines and policies that clai ...
method for
controlling pests using
solar power
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic e ...
to increase the soil temperature to levels at which many soil-borne
plant pathogen
Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...
s will be killed or greatly weakened.
Soil solarization is used in warm climates on a relatively small scale in gardens and
organic farms. Soil solarization weakens and kills
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
,
nematode
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...
s, and insect and mite pests along with weeds in the soil by
mulching
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area.
A mu ...
the soil and covering it with a tarp, usually with a transparent
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
cover to trap solar energy. This energy causes physical, chemical, and biological changes in the soil community.
Soil solarization is dependent upon time, temperature, and soil moisture.
It may also be described as methods of
decontaminating soil or creating
suppressive soils by the use of sunlight.
Soil disinfestation
Soil solarization is a hydrothermal process of disinfecting the soil of pests, accomplished by solar power (referred to as solar heating of the soil in early publications) and is relatively a new soil disinfestation method, first described in extensive scientific detail by Katan in 1976. The mode of action for soil solarization is complex and involves the use of heat as a lethal agent for soil pests from the use of transparent polyethylene tarps.
To increase the effectiveness of solar heating requires optimal seasonal temperatures, mulching during high temperatures and solar irradiation, and moisture soil conditions. Soil temperatures are lower when decreasing in soil depth and it is necessary to continue the mulching process to control for pathogens. Soil solarization practices requires soil temperatures reach 35-60
degrees Celsius
The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...
(95 to 140° F), which kills pathogens at the top 30 centimeters of soil.
Solarization does not sterilize the soil completely. Soil solarization enhances the soil towards promoting
beneficial microorganism.
Soil solarization creates a beneficial microbe community by killing up to 90% of pathogens.
More specifically, a study reported after eight days of solarization 100% of ''
V. dabliae'' (a fungus that causes farm crops to wilt and die) was killed at a depth of 25 centimeters.
Soil solarization causes a decrease in beneficial microbes, however beneficial bacteria like the ''
Bacillus
''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacilli ...
'' species are able to survive and flourish under high temperatures in solarized soils.
Other studies have also reported an increase in ''
Trichoderma harzianum
''Trichoderma harzianum'' is a fungus that is also used as a fungicide. It is used for foliar application, seed treatment and soil treatment for suppression of fungal pathogens causing various fungal plant diseases. Commercial biotechnological p ...
'' (fungicide) after solarization.
Soil solarization allows for the recolonization of competitive beneficial microbes by creating a favorable environment conditions. The number of beneficial microbes increases over time and makes solarized soils more resistant to pathogens.
The success of solarization is not only due to the decrease in soil pathogens, but also to the increase in beneficial microbes such as ''Bacillus'', ''
Pseudomonas
''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able ...
'', and ''
Talaromyces flavus''.
Soil solarization has been shown to suppress soil pathogens and cause an increase in plant growth. Suppressed soils promote
rhizobacteria
Rhizobacteria are root-associated bacteria that can have a detrimental (parasitic varieties), neutral or beneficial effect on plant growth. The name comes from the Greek ''rhiza'', meaning root. The term usually refers to bacteria that form symbio ...
and have shown to increase total dry weight in sugar beets by 3.5 times.
Also the study showed that
plant growth promoting rhizobacteria on sugar beets treated with soil solarization increased root density by 4.7 times.
Soil solarization is an important agricultural practice for ecologically friendly soil pathogen suppression.
Soil decontamination
A 2008 study used a solar cell to generate an electric field for electrokinetic (EK) remediation of
cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
-
contaminated soil
Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity ...
. The solar cell could drive the
electromigration
Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is important in applications where high direc ...
of cadmium in contaminated soil, and the removal efficiency that was achieved by the solar cell was comparable with that achieved by conventional power supply.
In Korea, various remediation methods of soil slurry and groundwater contaminated with
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
at a polluted gas station site were evaluated, including a solar-driven, photocatalyzed reactor system along with various
advanced oxidation process
Advanced oxidation processes (AOPs), in a broad sense, are a set of chemical treatment procedures designed to remove organic (and sometimes inorganic) materials in water and wastewater by oxidation through reactions with hydroxyl radicals (·OH) ...
es (AOP). The most synergistic remediation method incorporated a solar light process with
TiO2 slurry and
H2O2 system, achieving 98% benzene degradation, a substantial increase in the removal of benzene.
History
Attempts were made to use solar energy for controlling disease agents in soil and in plant material already in the ancient civilization of
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
. In 1939, Groashevoy, who used the term "solar energy for sand disinfection," controlled ''Thielaviopsis basicola'' upon heating the sand by exposure to direct sunlight.
Soil solarization is the third approach for soil
disinfestation; the two other main approaches,
soil steaming and
fumigation
Fumigation is a method of pest control or the removal of harmful micro-organisms by completely filling an area with gaseous pesticides—or fumigants—to suffocate or poison the pests within. It is used to control pests in buildings (s ...
; were developed at the end of the 19th century. The idea of solarization was based on observations by extension workers and farmers in the hot
Jordan Valley
The Jordan Valley ( ar, غور الأردن, ''Ghor al-Urdun''; he, עֵמֶק הַיַרְדֵּן, ''Emek HaYarden'') forms part of the larger Jordan Rift Valley. Unlike most other river valleys, the term "Jordan Valley" often applies just to ...
, who noticed the intensive heating of the polyethylene-mulched soil. The involvement of
biological control
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...
mechanisms in pathogen control and the possible implications were indicated in the first publication, noticing the very long effect of the treatment. In 1977, American scientists from the
University of California
The University of California (UC) is a public land-grant research university system in the U.S. state of California. The system is composed of the campuses at Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Francisco, ...
at Davis reported the control of ''
Verticillium
''Verticillium'' is a genus of fungi in the division Ascomycota, and are an anamorphic form of the family Plectosphaerellaceae. The genus used to include diverse groups comprising saprobes and parasites of higher plants, insects, nematodes, mo ...
'' in a cotton field, based on studies started in 1976, thus denoting, for the first time, the possible wide applicability of this method.
The use of polyethylene for soil solarization differs in principle from its traditional agricultural use. With solarization, soil is mulched during the hottest months (rather than the coldest, as in conventional
plasticulture
The term plasticulture refers to the practice of using plastic materials in agricultural applications. The plastic materials themselves are often and broadly referred to as "ag plastics". Plasticulture ag plastics include soil fumigation film, i ...
which is aimed at protecting the crop) in order to increase the maximal temperatures in an attempt to achieve lethal heat levels.
In the first 10 years following the influential 1976 publication, soil solarization was investigated in at least 24 countries
[
] and has been now been applied in more than 50, mostly in the hot regions, although there were some important exceptions. Studies have demonstrated effectiveness of solarization with various crops, including vegetables, field crops, ornamentals and fruit trees, against many pathogens, weeds and a soil arthropod. Those pathogens and weeds which are not controlled by solarization were also detected. The biological, chemical and physical changes that take in solarized soil during and after the solarization have been investigated, as well as the interaction of solarization with other methods of control. Long-term effects including biological control and increased growth response were verified in various climatic regions and soils, demonstrating the general applicability of solarization.
Computerized
simulation
A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of Conceptual model, models; the model represents the key characteristics or behaviors of the selected system or proc ...
models have been developed to guide researchers and growers whether the ambient conditions of their locality are suitable for solarization.
Studies of the improvement of solarization by integrating it with other methods or by solarizing in closed glasshouses, or studies concerning commercial application by developing mulching machines were also carried out.
The use of solarization in existing orchards (e.g. controlling ''
Verticillium
''Verticillium'' is a genus of fungi in the division Ascomycota, and are an anamorphic form of the family Plectosphaerellaceae. The genus used to include diverse groups comprising saprobes and parasites of higher plants, insects, nematodes, mo ...
'' in
pistachio
The pistachio (, ''Pistacia vera''), a member of the cashew family, is a small tree originating from Central Asia and the Middle East. The tree produces seeds that are widely consumed as food.
''Pistacia vera'' is often confused with other sp ...
plantations) is an important deviation from the standard preplanting method and was reported as early as 1979.
References
Further reading
*{{cite book, title=Soil Solarization, last1=Katan, first1=Jaacov, last2=DeVay, first2=James E., isbn=9780849368684, year=1991, publisher=
CRC Press
The CRC Press, LLC is an American publishing group that specializes in producing technical books. Many of their books relate to engineering, science and mathematics. Their scope also includes books on business, forensics and information tec ...
Earth sciences
Soil
Soil improvers