Pequi shell biochar in seedling production: effects of pyrolysis temperatures on substrate properties and the germination of Anadenanthera colubrina

Abstract

Abstract The valorization of agroforestry residues, such as Caryocar brasiliense (pequi) shells, through biochar production represents a promising strategy for developing sustainable substrates for forest seedling production. This study aimed to evaluate the effects of incorporating pequi shell biochar, produced at different pyrolysis temperatures (350, 400, and 450 °C), on the physicochemical properties of substrates and the germination performance of Anadenanthera colubrina (angico-vermelho) seeds. A total of 26 substrate formulations were tested, containing different proportions of biochar (2.5, 5, 7.5, and 10% v/v), combined with subsoil and commercial substrate. The results showed that increasing the pyrolysis temperature led to higher pH, cation exchange capacity (CEC), and availability of nutrients (P, K, Ca, Mg), significantly improving germination conditions. Principal Component Analysis (PCA) revealed a positive correlation between germination performance and attributes such as pH, CEC, P, Ca, and Mg, and a negative correlation with aluminum content. The treatment with 5% biochar produced at 450 °C combined with commercial substrate yielded the highest emergence rates. It is concluded that pequi shell biochar, especially when produced at higher pyrolysis temperatures, has high potential as an input for substrate formulation in the production of Anadenanthera colubrina seedlings, with promising applications for other forest species as well.