Conversion of anaerobic digestates into biochar for sustainable fodder production in soilless agriculture

Abstract The valorization of anaerobic digestates through slow pyrolysis offers a sustainable pathway for agricultural systems. This study assessed the effects of digestate type (swine, cattle, and dairy) and pyrolysis temperature (400, 500, and 600 °C) on biochar properties and evaluated their impact on maize ( Zea mays ) fodder grown under hydroponic-like soilless conditions. Thirty-six treatments were evaluated in a factorial design combining digestate source, temperature, and application rate (0–6.25 g per container). Biochar from dairy digestate (BDST) pyrolyzed at 500 °C exhibited the most favorable characteristics, with high carbon content (60.4%), low electrical conductivity (≈ 916 µS cm −1 ), and improved water and nutrient retention. At an application rate of 6.25 g per container, BDST–500 also achieved the highest SPAD and dry mass values. In contrast, swine- and cattle-derived biochars presented higher ash and salinity, reducing their agronomic performance. Multivariate analysis indicated that digestate type was the main determinant of plant physiological performance, beyond the individual effects of pyrolysis temperature and application rate. Overall, dairy-derived biochar demonstrates strong potential as a functional amendment for hydroponic fodder systems and as a tool to advance circular bioeconomy practices. Graphical abstract