No abstract

Recently, biochar has been widely used for versatile applications in agriculture and environment sectors as an effective tool to minimise waste and to increase the efficiency of circular economy. In the present work, we review the current knowledge about biochar role in N, P and K cycles. Ammonia volatilisation and N 2 O emission can be reduced by biochar addition. The content of available P can be improved by biochar through enhancement of solubilisation and reduction in P fixation on soil mineral, whilst high extractable K in biochar contributes to K cycle in soil. Liming effect and high CEC are important properties of biochars improving beneficial interactions with N, P and K soil cycle processes. The effectiveness of biochar on N, P and K cycles is associated with biochar properties which are mainly affected by feedstock type and pyrolysis condition.

Biochar is utilized in modern society for multiple agricultural and environmental purposes in the framework of circular economy. The aims of this study were to review the leading edge of knowledge of studies where biochar was used in the agriculture sector, as an input for growing media, composting and to improve soil physical and chemical properties along with crop yield. Usage of biochar is promising as substitute for peat and in the composting as it reduces N losses, accelerates the process and improves the quality of final composts. The right selection of feedstock and optimization of pyrolysis conditions are key factors to tailor biochar thereby improving soil properties and increasing crop yield. Potential benefits and flaws for the usage of biochar technology in the agricultural domain are broadly reviewed and thoroughly discussed.

Charcoal production in forests is one of the oldest forms of forest exploitation. The legacy of such once widespread activity is a plethora of relic charcoal hearths (RCHs 1), where soil shows a thick, black, charcoal-rich top horizon. Even where very common, such as in European forests, RCHs were rarely studied to assess their relevance as C reservoir. For this purpose, as a case study, we investigated some RCHs at Marsiliana, a typical Mediterranean oak forest from Central Italy. We found that RCHs soils, in spite of representing < 0.5% of total surface, gave a substantial contribution in terms of C, i.e. 1.1% to 4.2% of total ecosystem C, including litter, the top 30 cm of soil, deadwood, aboveground and belowground biomass. On average, soil C content in RCHs was eight times higher than the soil outside the RCHs. The environmental significance of RCHs soils appears still greater considering that, on average, 43% of their C stock was charcoal, a form of C highly recalcitrant to mineralization. These results would stress the importance of accounting for the contribution of RCHs in terms of soil C and giving an estimation of their charcoal content in future C inventories, both as macroscopic and microscopic particles in soil. This study support the necessity of safeguarding the anthropogenic soils of RCHs as a precious C reservoir as well as a memory of past land uses.