The Soil Solarization (Solar heating)

(Updated April 2013)

Soil solarization (also referred to as solar heating of the soil in early publications) is a new soil disinfestation method, first described in 1976 by Katan et al., for controlling soilborne pathogens and weeds, mostly as a pre-planting soil treatment. It was opened to scientific examination and criticism via a publication in Phytopathology in 1976. Soil solarization is achieved by covering (mulching, tarping) the soil with transparent polyethylene during the hot season, thereby heating it and killing the pests. The 1976 publication described in detail the method, its principles and potential in disease and weed control under field conditions. The concept of soil solarization could only have evolved following the advances in plasticulture development, especially in plastic mulch technology, which had begun two decades earlier. The basic approach of using the sun to heat mulched soil for pest control has taken off since then and has been adopted based on fundamental research, accompanied by extensive implementation under various cropping systems and in different regions. Over the years, solarization has been assessed as a control method against a wide range of soilborne pests, including phytopathogenic fungi, such as Verticillium, Fusarium, Pythium, pathogenic bacteria, nematodes, weeds and others. Although, soil solarization is effective in controlling a variety of pests, there are cases in which effective control has not been achieved. Adoption of solarization has increased significantly since 1976, despite the fact that this technology does not enjoy industry support. On the other hand, the methyl bromide crisis and its phase-out have raised challenges and initiated new opportunities, especially with intensive cropping practices. One outcome is that soil solarization (alone and especially when combined) has become an important player in the soil disinfestation arena.

Soil solarization is the third approach for soil disinfestation; the two other main approaches, soil steaming and fumigation, physical and chemical approaches, respectively, were developed at the end of the 19th Century. Soil fumigation was identified for many years with the fumigant methyl bromide. It comes as no surprise, therefore, that the phase-out of methyl bromide, along with extensive efforts to find effective chemical and nonchemical alternatives for pest control, has further emphasized the limitations of using available fumigants and other disinfestation methods as stand-alone approaches. The last decades have seen adoption of the integrated pest management (IPM) philosophy for soil disinfestation as the outcome of the realization that, beyond killing the pathogen, soil disinfestation should encompass economic, social, legislative, and environmental aspects. IPM in soil disinfestation represents a continuous process rather than a single action, and brings together the application of various control measures and concepts. Combining solarization with other pest-control measures is one of the important tools for IPM implementation and improvement in soil disinfestation. The various strategies of combining soil solarization with pesticides, organic amendments or beneficial microorganisms, including the integration of soil solarization into cropping systems under real farming conditions, has been extensively reported.

Today, solarization is explored or implemented in more than 70 countries and studies have been documented in over 1400 research papers, mostly in the hot regions, although there were some important exceptions. The studies demonstrated the effectiveness of solarization with various crops (vegetables, field crops, ornamentals, nurseries and fruit trees) against many pathogens, weeds and soil arthropods, in various cropping systems including organic farming. Pathogens and weeds which are not controlled by solarization were also detected. In parallel, the biological, chemical and physical changes taking place in the solarized soil during and after the solarization process, interactions with other methods of control and many other topics, were investigated. Some findings, e.g. long-term effects, biological control and increased growth response were verified in various climatic regions and soils. This demonstrates involvement of general mechanisms in solarization, and the wide applicability of this approach.

Both physical and biological mechanisms, mainly microbial, are involved in pathogen control by solarization. Frequently, populations of fluorescent pseudomonad bacteria, Bacillus sp. and the antagonistic fungus Talaromyces and other antagonists were increased by solarization, either in the soil or in the rhizosphere of the plants. Frequently, the solarized soil becomes more suppressive. Phenomena of increased mineral nutrients, e.g. N, K and Ca, as well as improved growth of the plant in the solarized soil, even in the absence of known pathogens, were also reported. Induced resistance in plants growing in solarized soils is also reported.

Computerized simulation models for predicting temperatures of solarized soils were developed, and can be used as guidelines by researchers and growers which are interested to employ solarization, and are not sure whether the ambient conditions in their place are suitable for solarization. In addition, simulation models and approaches for predicting rate of thermal killing of pathogens and rate of pathogen control by solarization were developed.

Studies of the improvement of solarization by integrating it with other methods or by its application 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, olive or avocado plantations) which was reported as early as 1979, is an important improvement and deviation from the standard preplant method. Soil solarization can be improved by a variety of means: solarizing the soil in a closed greenhouse, using a double layers mulching, using special types of improved plastic films, etc. Sprayable plastic material was also developed. In addition to soil disinfestation, solarization is being developed for additional purposes. These include solar sanitation of the greenhouse structure, sanitation of agricultural tools, disinfesting water, controlling animal and human pathogens, solarizing piles of growth substrate material, nurseries etc.

Soil solarization, as a control method, has advantages and impediments. It is a nonchemical method without endangering the user or the environment, simple for application and less expensive than many fumigation methods. Its major limitation is its climate dependency and that the soil cannot be occupied with crops for several weeks. Although no major negative side effects by this method were reported, such a possibility should not be excluded. Therefore, solarized fields should be continuously monitored, as it should with all the disinfested fields.

It should be emphasized that soil solarization is not a magic tool which cures every illness but rather one more tool for pest management which under the appropriate conditions and application can become an important additional tool to our rather limited arsenal of management tools for soil-borne pests.

For further information please see the following websites:

http://ucanr.org/sites/Solarization/

Selected references.

Chen Y., Gamliel, A., Stapleton, J. J. & Aviad T. 1991. Chemical, physical and microbial changes realted to plant growth in disinfested soils. Pages103-129 in: Soil Solarization. J. Katan & J. E. DeVay,Eds. CRC Press, Boca Raton, FL.

DeVay, J. E., Stapleton, J.J. & & Elmore, C. L. 1991. Soil Solarizaiton, Proceeding, First International Conference on Soil Solarizaton, Amman, Jordan. FAO Plant Production and Protection Paper 109. FAO Rome.

Elmore, C. L., Stapleton, J.J., Bell, C. E., DeVay, J. E., and Hart, W. H. 1984. Soil solarization: A non chemical method for controlling disease and pests. Cooperative Extension, Division of Agriclture and Natural Resources: Leaflet 21377, University of California, Oakland, 14 pages.

Eshel D., Gamliel, A., Grinstein, A., Di Primo, P., and Katan, J. 2000. Combineed soil treatments and sequence of application in improving the control of soilborne pathogens. Phytopathology 90:751:757

Gamliel, A., and Katan. 1991. Involvement of fluorescent pesudomonads and other microorganisms in increased growth response of plants in solarized soils. Phytopathology 81:494-502.

Gamliel, A., and Katan. 2009. Control of plant disease through soil solarization. Pages 196-220 in Disease control in Plants: Biologically and Environmetally friendly approaches. D. Walter, Ed. Wiley-Blackwell, Oxford.

Gamliel A., and Katan. J. 2012. Soil Solarization: Theory and Practice. APS Press St. Paul MN.

Gamliel, A., and Stapleton. J. J. 1993. Effect of chicken compost or ammonium phosphate and solarizalion on pathogen control, Rhizosphcrc microorganisms, and lettuce growth. Plant Dis. 77:886-891.

Gamliel, A., Vanachter, A., and Katan, J. 2010. (eds.) Chemical and Non-Chemical Soil and Substrate Disinfestation Acta Hort 883. ISHS, Leuven Belgium (429 pages).

Grinstein, A. 1992. Introduction of a new agricultural technology - soil solarization - in Israel. Phytoparasitica 20.Suppl.:127S-131S.

Grinstein, A. & A. Hetzroni. 1991. The technology of soil solarization. Pages 159-170 in J. Katan & J. E. DeVay (eds.) Soil Solarization. CRC Publications, Boca Raton.

Gullino, M.L., Katan, J., and Matta, A. 2000. (eds.) Chemical and Non-Chemical Soil and Substrate Disinfestation Acta Hort 532. ISHS, Leuven Belgium (256 pages).

Katan, J. 1981. Solar heating (solarization) of soil for control of soilborne pests. Annu. Rev. Phytopathol. 19:211-236

Katan, J & J. E. DeVay. 1991. (eds.) Soil Solarization. CRC Publications, Boca Raton: 159-170.

Katan, J., A. Greenberger, H. Alon & A. Grinstein. 1976. Solar heating by polyethylene mulching for the control of diseases caused by soil-born pathogens. Phytopathology 66:683-688.

Katan, J., A. Grinstein, A. Greenberger, O. Yarden & J. E. DeVay. 1987. First decade (1976-1986) of soil solarization (solar heating)-A chronological bibliography. Phytoparasitica 15:229-255.

Grunzweig, J. M. Rbinowitch, H. D., and Katan J. 1993. Physiological and developmental aspects of increased plant growth in solarized soils. Ann. Appl. Biol. 122:579-591

Stapleton, J.J. and DeVay, J.E. 1986. Soil solarization: a nonchemical approach for the management of plant pathogens. Crop Prot. 5:190-198.

Stapleton, J.J., DeVay, J.E., and Elmore, C.L. 1998. (eds.) Soil Solarization and Integrated Management of Soilborne Pests. Plant Production and Protection Paper 147, FAO, Rome. 656 pp.

Tjamos, E. C. Grinstein, A., and Gamliel A. 1999. Disinfestation of soil and growth media. Pages 130-149 in: Integrated pest management in Greenhouse Crops. R. Albajes, M L. Gullino, J. C. Van Lantern and Y. Elad. Eds. Kluwer Academic Publishers, Dordrecht, the Netherlands

Tjamos, E. C., and Paplomatas, E. J. 1988. Long-term effect of soil solarization in controlling Verticillium wilt of globe artichokes in Greece. Plant Pathol. 37:507-515.