University of California

Overview of soil solarization

In modern agriculture, urban residents and farmers are often located near each other. Many people are concerned about the use of agricultural pesticides, and the possibility of health and environmental hazards resulting from pesticide residues in the air, water, soil, and in the crops themselves.
Because of these concerns, numerous agricultural chemicals which farmers have relied upon for many years have been restricted or banned. Several of these chemicals are pesticides which are used to kill harmful fungi, bacteria, nematodes, weeds, and certain insects in soil, and/or which increase crop yields. Methyl bromide is one such soil fumigant scheduled for phaseout over the next few years. Farmers need useful alternative treatments for managing soilborne pests.
fumigated field
Research done over the past 20 years in many Mediterranean, desert, and temperate locations around the world has shown that soil solarization, a hydrothermal process of heating moist soil, can successfully disinfest soil of pests. Solarization can be used alone, or in combination with other chemical or biological agents as the framework for an IPM program for soilborne pests in high-value horticultural crops grown in greenhouses and open fields.
Solarization may also be used for producing disease and pest-free planting material in nurseries and seedbeds. 
This technique is especially useful in developing countries, where placing simple plastic tents over containerized soil during periods of hot air temperature can eliminate pests without need for hazardous chemicals or intensive training of users.
In another use, seedbeds are being disinfested of pests by solarization in a nursery in South America.
Although solarization can be a very useful strategy
to help replace chemical fumigants and develop integrated pest management programs, there are limitations on its usefulness. Current limitations include nonconducive climatic zones which limit soil heating, reduced heating deeper in soil, and plastics disposal.
Researchers in our informal workgroup moving forward with new ideas and techniques to further the benefits of solarization and IPM to world agriculture.
Some experimental uses of solarization include treatment of orchard soils, either prior to planting or during establishment.
Another experimental approach under evaluation is use of biodegradable spray mulches, rather than plastic films. Solarization as a useful tactic for helping growers produce healthy, abundant crops. Nevertheless, it is important that solarization be considered not as a "stand alone" technology, but rather as a dynamic, developing component of integrated pest management systems. 
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