Solarization is a method for soil disinfestation, taking effect by increased soil temperatures under soil covers of transparent polyethylene sheets during the period of intense solar irradiation. Four field experiments were set up in the state of São Paulo, Brazil (districts of Mogi das Cruzes, Jarinú, Piracicaba and Itatiba), in the years 2000 and 2001, to evaluate the effects of soil solarization on physical, chemical and biological soil properties. Solarization caused a significant reduction in penetration resistance of the evaluated soils in Jarinu, Piracicaba, and Itatiba. In Jarinu, measurements carried out eight months after the removal of the plastic sheet showed that the effect of solarization on penetration resistance was still similar to that observed in the first evaluation. However, in Mogi das Cruzes, in an organic soil, solarization increased the soil's penetration resistance in the 2.5-5.0 cm layer. Solarization did not affect the macro-, micro- and total porosity of soils in Piracicaba and Jarinu, where these properties were measured, however it did reduce the apparent density. In an evaluation by fluorescein diacetate hydrolysis, the microbial activity in the soil proved to decrease by solarization. In Mogi das Cruzes, the suppressiveness to Fusarium oxysporum f. sp. phaseoli was evaluated in vitro by colonizing soil samples with an isolate marked with benomyl resistance. Solarization reduced the recovery of the pathogen, indicating an increase in suppressiveness. In solarized plots, there was a significant increase in the concentration of NH4+-N in all experiments, of Mn in three, of NO3--N, Mg2+, and base saturation in two, and K+ in one experiment. On the other hand, the concentration of Cu, Fe, and H + Al decreased in two places, and Zn in one. Results showed that solarization caused changes in physical, chemical and biological soil properties, improving the soil structure, releasing nutrients, and increasing disease suppressiveness.
resistance to penetration; suppressiveness; physical control
