Soil Solarization Introduction

Soil-applied pesticides have been successfully used to control soilborne diseases, weeds, and nematodes in most vegetable and fruit crops over the past decades. Toxicity of these materials to animals and humans and their environmental and economic costs (Pimentel et al. 1992; Ruzo 2006) raised serious environmental and human safety concerns, leading to the phase-out of the most effective and largely used chemical, the methyl bromide (Luken and Grof 2006), and the increasing restrictions on the applications of available pesticides (Perkins and Patterson 1997). The limited availability of chemicals resulted in an increased emphasis on reduced-pesticide or nonpesticidal control methods and, therefore, renewed the interest of farmers and researchers on soil solarization as a simple, environmentally safe, and effective nonchemical control tool.

Mulching soil with plastic films was known since the early 1960s of the past century as an agronomical technique to reduce soil water evaporation and erosion and improve soil physical properties (Waggoner et al. 1960; Burrows and Larson 1962; Lai 1974), whereas control of soil and plant material disease agents by the use of heat, also generated by solar energy, was reported still earlier (Grooshevoy 1939; Newhall 1955). However, soil solarization as actually meant, namely, a technology for soil disinfestation from soilborne pathogens and weeds, originated during the 1970s from the studies conducted in Israel and Jordan (Katan et al. 1976). In the first decade following the publication of Katan et al., a large number of studies focused on the effectiveness of solarization against many soilborne pathogens, weeds, and soil arthropods in many vegetable, field, ornamental, and fruit tree crops. Physical, chemical, and biological principles of solarization and collateral biological, chemical, and physical changes occurring in the soil during and after the solarization process were also largely investigated (Katan et al. 1987; DeVay 1991) (Fig. 9.1). Most of these solarization studies were undertaken in the mediterranean and Middle East countries, namely, Israel (Grinstein and Ausher 1991), Italy (Garibaldi and Gullino 1991), Spain (Bello et al. 2001), Greece (Tjamos et al. 2000), and California (Stapleton and DeVay. 1986), but many reports originated also from many other countries, including also cooler climate areas (Garibaldi and Tamietti 1984). Moreover, trials involved either field or greenhouse cropping systems and were also successfully extended to the disinfestation of seedbeds,

Fig. 9.1 Plots solarized with a polyethilene plastic film in a field solarization trial in Southern Italy (courtesy of dr Nicola Greco)

containerized planting media, and cold frames (Stapleton 2000). Due to the increasing success of concepts of integrated management of agricultural pests (Kogan 1998), research of the following decades generally regarded at solarization as a component of more complex control strategies rather than as a stand-alone technique (Stapleton and DeVay 1995; Chellemi 1998), with the aim to improve the effect of solar heating treatment and overcome its technical and economical limits through the combination with other control methods (Sikora et al. 2005).

Soil solarization can easily be described as a process in which the solar radiation is trapped under a plastic soil mulch during periods of high ambient temperature, causing an increase of temperatures in the upper soil layers to levels lethal or sub-lethal to soilborne pathogens and weeds. Despite the apparently simple technology, research evidenciated as the effects of soil solarization result from different and complex mechanisms and are affected by a great number of environmental and technical factors, primarily soil temperatures and type of plastic films. Moreover, in addition to soilborne pathogens and pests control, a set of physical, chemical, and biological changes were documented to be raised by solarization in the soil, as influencing soil physical and chemical properties and crop yield.

The aim of this chapter is to provide, according to literature available up to the early months of 2008, an up-to-date review of the above aspects of soil solarization, from the mechanisms and related factors to the effects on different target organisms and soil properties. Moreover, as integrated pest management is a fundament of sustainable agriculture, studies on the potential integration of solarization with other control tools were also largely documented.

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