Biochar, a solid product from the thermal conversion of biomass, can be used as a climate change mitigation strategy, since it can sequester carbon from the atmosphere and store it in the soil. The aim of this study is to assess the potential of biochar as a mitigation strategy in the long term, by modelling the results obtained from an 8-year field experiment. As far as we know, this is the first time that a model for biochar degradation has been validated with long-term field data.