Assessment of the biochemical degradability of crop derived biochars in trace elements polluted soils

páginas.- 3 figuras.- 4 tablas.- 71 referencias.- Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jaap.2021.105186This study assesses the biochemical degradability of biochars produced from five contrasting crop residues (rice husk, olive pit, almond shell, maize straw and wood chips) in acidic soils contaminated with trace elements. For this purpose, highly and moderately acid soils were amended with each of the proposed biochars and subjected to a microbial degradation experiment under controlled conditions for 155 days. CO2 production of pure biochars fitted with a single exponential model, indicating that they only had one C pool. Among the biochars studied, those derived from olive pit and almond shell showed the greatest stability, with mean residence times (MRT) of 293 and 214 years, respectively, whereas, maize straw biochar revealed MRT of 82 years. Despite that the average MRT of all tested biochars under controlled conditions were shorter than usually reported, biochar addition increased the MRT of the recalcitrant C pool of the studied soils by a factor from 2x to 13 × . Solid-state 13C NMR spectra confirmed a partial cracking of the biochar aromatic network during the experiment due to microbial degradation or physical alteration processes. It was further noted that biochar degradability depended on its aromaticity but we have also observed that in highly acidic and metal-contaminated soils biochar is less degraded, probably due to the difficulties for microbial development at these soils.The Spanish Ministry of Economy, Industry and Competitiveness (MINEICO) and AEI/FEDER are thanked for funding the projects CGL2016-76498-R and CGL2015-64811-P. P. Campos thanks the “Fundación Tatiana Pérez de Guzmán el Bueno” for funding her PhD contract. MINEICO is also thanked for funding the “Ramón y Cajal” post- doctoral contract of José M. De la Rosa. Desiré Monis Carrere and Alba Carmona Navarro are thanked for technical assistant in performing the elemental analysis measurements. The companies “Cooperativa Nuestra Señora de los Ángeles” (Montellano, Spain) and Orivarzea S.A. (Portugal) are thanked for providing the olive pits and rice husk, respectivelyPeer reviewe