<p>It is estimated that over 37 % of degraded soils in the European Union are polluted by heavy metals [1], which are non-biodegradable and persistent pollutants in soils. The application of organic amendments to soils for their remediation has been worldwide used [2]. Several studies have shown that biochar, the carbonaceous material produced by pyrolysis of organic residues, has a high potential to stabilize trace elements in soils [3]. Biochars usually have an alkaline pH and high water holding capacity (WHC), large specific surface area and cation exchange capacity, which are appropriate characteristics to reduce the availability of heavy metals in the environment [4]. Nevertheless, recent studies exhibited that biochar recalcitrance could be much lower than assumed [5].  Beside this, the effects of the addition of biochar as a soil amendment on the composition of soil organic matter (SOM) are largely unknown. Thus, the aim of this study is to investigate the effects of the application of biochars from rice husk (RHB) and olive pit (OPB) in a Typic Xerofluvent polluted with trace-elements after 24 months at field in 12 plots installed at the surroundings of the Guadiamar Green Corridor (37° 23' 7.152"N, 6° 13' 43.175"; Southwest Spain). Specifically, for this study the effects of biochar amendment on soil physical properties (pH, water holding capacity-WHC, moisture, etc), elemental composition, total SOM, the content of oxidizable SOM as well as the content and composition of humic acids (HAs) have been assessed.</p><p>Biochar application caused an increase in soil pH (around 0.4 units), soil moisture (from 6-7% to 10-18 %) and WHC. In addition, the total organic carbon and HAs content increased slightly. Preliminary results show that biochar could become part of the humified SOM in a shorter time than initially expected. Nevertheless, the spectroscopic analyses (FT-IR and <sup>13</sup>C NMR spectroscopy) documented that the qualitative composition of soil HAs was not altered due to the biochar amendment.</p><p><strong> </strong></p><p><em>References</em>:</p><p>[1] EEA; 2007. CSI 015. Copenhagen, Denmark: European Environmental Agency.</p><p>[2] Madejón, E.; Pérez de Mora, A.; Burgos, P.; Cabrera, F.; 2006. Environ. Pollut. 139, 40-52.</p><p>[3] Campos, P., De la Rosa, J.M., 2020. Sustainability 12, 6025.Uchimiya, M.; Klasson, K.T.; Wartelle, L.H.; Lima, I.M.; 2011. Chemosphere 82, 1438-1447.</p><p>[4] Campos, P., Miller, A.Z., Knicker, H., Costa-Pereira, M.F., Merino, A., De la Rosa, J.M., 2020. Waste Manag. 105, 256-267.</p><p>[5] De la Rosa, J.M.; Rosado, M.; Paneque, M.; Miller, A.Z.; Knicker, H.; 2018. Sci. Tot Environ. 613-614, 969-976.</p><p><em>Acknowledgements</em>: The Spanish Ministry of Economy, Industry and Competitiveness (MINEICO), CSIC and AEI/FEDER are thanked for funding the project CGL2016-76498-R. P. Campos thanks the “Fundación Tatiana Pérez de Guzmán el Bueno” for funding her PhD.</p>