Soil solarization is an environmentally friendly method of using solar power for controlling pests such as soilborne plant pathogens including fungi, bacteria, nematodes, and insect and mite pests along with weed seed and seedlings in the soil by mulching the soil and covering it with tarp, usually with a transparent polyethylene cover, to trap solar energy. It may also describe methods of decontaminating soil using sunlight or solar power. This energy causes physical, chemical, and biological changes in the soil.
Soil solarization (referred to as solar heating of the soil in early publications) is a relatively new soil disinfestation method, first described in extensive scientific detail by Katan et al. in 1976, presenting the results of a series of studies performed under field conditions, initiated in 1973, for controlling soilborne pathogens and weeds, mostly as a pre-planting soil treatment. Soil is mulched and then covered with transparent polyethylene during the hot season, thereby heating it and killing the pests.
A 2008 study used a solar cell to generate an electric field for electrokinetic (EK) remediation of cadmium-contaminated soil. The solar cell could drive the electromigration 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 at a polluted gas station site were evaluated, including a solar-driven, photocatalyzed reactor system along with various advanced oxidation processes (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.
Attempts were made to use solar energy for controlling disease agents in soil and in plant material already in the ancient civilization of India. 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; 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, who noticed the intensive heating of the polyethylene-mulched soil. The involvement of biological control 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 at Davis reported the control of Verticillium 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 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 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 in pistachio plantations) is an important deviation from the standard preplanting method and was reported as early as 1979.
How to Solarize Soil
The area to be solarized should be level and free of debris and large clods. The soil should be watered if the soil is dry. The soil should not be saturated but have the crumbly damp look that the soil would have at planting. Place clear plastic over the soil surface and bury the edges in a foot deep trench. The plastic can be clear construction grade plastic and vary in thickness from 1 to 6 mils. The thinner plastic (1-2 mils) will allow better soil heating since it will reflect less solar energy but may allow weeds to grow right through it especially nut grass or Bermuda grass. The plastic should be left in place for 4–6 weeks. Solarization is most effective when done in June and July. However, depending on your geographic location, solarization may also be effective in May, August, and September.
Gardeners in more temperate regions first cover the soil with black plastic, then use a clear plastic panel designed to keep the clear plastic just inches above it. Clear plastic gives the "greenhouse effect" and the black plastic facilitates heat collection and transfer to the soil.
- Yuan S; Zheng Z; Chen J; Lu X (June 2008). "Use of solar cell in electrokinetic remediation of cadmium-contaminated soil". J. Hazard. Mater. 162 (2–3): 1583–7. doi:10.1016/j.jhazmat.2008.06.038. PMID 18656308.
- Cho IH; Chang SW (January 2008). "The potential and realistic hazards after a solar-driven chemical treatment of benzene using a health risk assessment at a gas station site in Korea". J Environ Sci Health a Tox Hazard Subst Environ Eng 43 (1): 86–97. doi:10.1080/10934520701750090. PMID 18161562.
- J. Katan et al. The first decade (1976–1986) of soil solarization (solar heating): A chronological bibliography. Phytoparasitica. 1987 Volume 15, Number 3, 229-255, doi:10.1007/BF02979585