Biomonitoring tools for biochar and biochar-compost amended soil under viticulture: Looking at exposure and effects

Benefits that biochar can bring to unirrigated vineyards are related mainly to soil chemistry, soil structure and water retention improvements. Little is still known about effects of biochar on soil biotic processes and organisms that mediate them. For a sustainable use of biochar in agriculture, alone or in combination with other soil amendments, there is a need for better understanding of soil-biochar-biota interactions, particularly in the long term. Here we applied an ecotoxicological monitoring programme to evaluate the effects of field plot-scale biochar and biochar-compost mixture into vineyard soil. Standard and well described laboratory bioassays were used, assessing the survival and reproduction of Folsomia candida and food consumption and biomass change of Porcellionides pruinosus. The present study examined the effects of biochar- and biochar-compost-enriched soil treatments in a commercial vineyard subjected to conventional pesticide management practices. We considered two sampling events, corresponding to: i) the time of initial application of fresh biochar and biochar-compost (T0); and ii) the 18 month-period after the application of the amendments (T18). Additionally, based on the time and rates of the pesticides application prior to the second sampling event, a theoretical exposure was estimated alongside with risk quotients. The risk quotients were elevated for certain active ingredients in the mixture (cyprodinil, propiconazole, copper oxychloride and copper sulfate). This corroborates the overall decrease in organisms' performance observed after they were exposed to the field-aged samples. The ecotoxicological response to the tested biochar and biochar-compost enriched soil was species-specific, time-dependent, and to some extent, treatment-dependent. The most sensitive endpoint obtained in the study was the reproduction output of F. candida. While freshly amended soil did not induce substantial changes on organisms' performance, the measured endpoints were significantly lower when the organisms were exposed to the treatments from the second sampling event which was subjected to various climatic factors and conventional pesticides. Regarding food consumption of P. pruinosus, and number of F. candida juveniles the effects were more pronounced in 40 t ha−1 biochar and biochar-compost amended treatments than in 4 t ha−1 treatment. Results of the study show that bioavailability of potentially toxic elements might not be prevented over time by the presence of biochar and biochar-compost in commercial vineyards that receive conventional plant protection products.