Evaluating plant-available P methods and quality characterization of biochar derived from manure and sewage sludge

Phosphorus(P) is essential yet limited, and Norway, like the rest of Europe, remains dependent on imported phosphate rock. Biochar from pyrolysis organic residues offers a potential alternative P source, although quantifying plant-available P is complicated by diverse P speciation. In this study, biochar produced at 400 °C from raw manure, manure digestate, and biologically treated sewage sludge digestate was evaluated using multiple P extraction methods (Olsen, Mehlich-3, ammonium lactate, citr