Biochar potential in reclaiming degraded soils

<p>Biochar is the solid residue produced by pyrolysis (thermal treatment under absence of oxygen) of biomass [1]. This material has been widely proposed for remediation of degraded soils [2]. Soil degradation comprises loss of chemical, physical and biological properties of soil, declining soil health. Soils that are polluted with high concentrations of trace elements present serious functional problems. It is estimated that 37 % of the degraded soils in Europe are polluted with trace elements [2]. This study aimed to determine the effects of biochar application into degraded acidic Fluvisols [3], that were polluted in April 1998 by the massive dumping of mine sludge contaminated with heavy metals, called the Aznalcóllar disaster. The studied soils were amended with 8 t ha<sup>-1</sup> of olive pit and rice husk biochars. After 6, 12 and 20 months under field conditions, both amended and un-amended soils were sampled for determining microbial diversity using the Illumina Miseq technology of the 16S rRNA gene. Soil properties, soil composition, enzymatic activities and plant development were also analysed. Physical properties of the degraded soils were improved by the application of biochars. Soil pH strongly influenced dehydrogenase and β–glucosidase activities. Biochars enhanced plant diversity and, more specifically, olive pit biochar increased plant yield in the more acidic soil. Differences in microbial communities were found between both soils and sampling campaigns. Moderately acidic soil showed greater alpha diversity comparing to the most acidic soil. In fact, after 6 months of biochar application, Bacteroidetes, Gemmatimonadetes and Verrucomicrobia were solely found in the moderately acidic soil. However, Shanon and Simpson index values showed that the application of biochars enhanced bacterial diversity in the most acidic soil after 6 months, which control sample was almost exclusively composed of Ktedonobacteria, belonging to the phylum Chloroflexi. Correlation coefficients explained that biochar amendment increased bacterial diversity by increasing soil pH. The effect of biochar on microbial communities was dissipated over time [4].</p><p> </p><p>References:</p><p>[1] IBI, 2015. IBI-STD-2.1. International Biochar Initiative.</p><p>[2] European Environment Agency, 2020. https://www.eea.europa.eu/themes/soil/soil-threats.</p><p>[3] Campos, P., De la Rosa, J.M., 2020. Sustainability 12, 6025.</p><p>[4] Campos, P., Miller, A.Z., Prats, S.A., Knicker, H., Hagemann, N., 2020. Soil Biol. Biochem. 150, 108014.</p><p> </p><p>Acknowledgements:</p><p>The former Spanish Ministry of Economy, Industry and Competitiveness (MINEICO) and AEI/FEDER are acknowledge for funding the project CGL2016-76498-R. J.M. De la Rosa thanks MINEICO for funding his “Ramón y Cajal” contract. “Fundación Tatiana Pérez de Guzmán el Bueno” for funding the PhD contract of P. Campos. A.Z. Miller thanks “Fundação para a Ciência e a Tecnologia” for its support.</p>