Soil solarization with biodegradabile materials and its impact on soil microbial communities.

Soil solarization (SS) seems one of the most promising techniques to control soilborne pathogens, but an important limitation to the diffusion of this technique is due to the drawback regarding the disposal of the used plastic materials. A possible solution to this problem is the use of biodegradable plastics. The aim of this study was compare the impact of SS with biodegradable materials with SS with plastic film and others pest management techniques (i.e. organic matter amendment, calcium cyanamide and Dazomet fungicide application) on crop productivity, soilborne disease incidence, weed suppression, and soil chemical (total N, ammonium, nitrate, available phosphorus, organic matter, hydrolysis of the fluorescein diacetate) and microbial parameters (cultivable Pseudomonas, DGGE fingerprinting of ribosomal DNA of soil bacteria and fungi). We carried out field experiments on two types of soil with different textures (clay and sandy) artificially inoculated with Fusarium oxysporum f.sp. lycopersici (vs. tomato) and Sclerotinia minor (vs. lettuce). Temperature of soils covered with solarizing materials was always higher than that of bare soils, but plastic cover was more effective and consistent in rising soil temperature compared to biodegradable materials. Plant growth promotion by SS was limited, especially compared to Dazomet and organic matter application, and a positive effect was observed only for lettuce in the clay soil. Differently, both plastic and biodegradable solarizing materials were effective in reducing lettuce drop caused by Sclerotinia minor. Weed development was significantly suppressed by Dazomet application and SS with plastic film, while weed control with biodegradable materials was limited. SS has a variable and limited effect on chemical and microbial parameters, with the exception of a general tendency of reduction of bacterial and fungal richness. Dazomet fungicide has the strongest effect on the soil microbial community, with the most pronounced diversity reduction in both soil types and a significant stimulation of the fluorescent Pseudomonas group. Organic amendment significantly enhanced organic matter content, the hydrolysis of the fluorescein diacetate and the Pseudomonas population. Among all measured soil parameters, fluorescent Pseudomonas population emerged as the most important parameter in relation to crop productivity. In conclusion, the results of this experimentation show the potential of using the biodegradable solarizing materials in place of plastic films, but also, indicate the need for improving their properties to obtain performances comparable to those of other pest management techniques