Combined ozonation and solarization for the removal of pesticides from soil: Effects on soil microbial communities.

Pesticides have been used extensively in agriculture to control pests and soil-borne diseases. Most of these pesticides can persist in soil in harmful concentrations due to their intrinsic characteristics and their interactions with soil. Soil solarization has been demonstrated to enhance pesticide degradation under field conditions. Recently, ozonation has been suggested as a feasible method for reducing the pesticide load in agricultural fields. However, the effects of ozonation in the soil microbial community have not been studied so far. Here, we evaluate the combined effects of solarization and ozonation on the microbial community of a Mediterranean soil. For this purpose, soil physico-chemical characteristics and enzyme activities and the biomass (through analysis of microbial fatty acids) and diversity (through 16S rRNA and ITS amplicon sequencing) of soil microbial communities were analyzed in a 50-day greenhouse experiment. The degradation of the pesticides was increased by 20%, 28%, and 33% in solarized soil (S), solarized soil with surface ozonation (SOS), and solarized soil with deep ozonation (SOD), respectively, in comparison to control (untreated) soil. Solarization and its combination with ozonation (SOS and SOD) increased the ammonium content as well as the electrical conductivity, while enzyme activities and soil microbial biomass were negatively affected. Despite the biocidal character of ozone, several microbial populations with demonstrated pesticide-degradation capacity showed increases in their relative abundance. Overall, the combination of solarization plus ozone did not exacerbate the effects of solarization on the soil chemistry and microbial communities, but did improve pesticide degradation.