Phytotoxicity and germination responses of Zea mays L. to anaerobically digested liquid biofertilizers derived from cattle manure and fish-processing sludge

Abstract Valorization of cattle manure and fish-processing sludge as liquid biofertilizers may contribute to waste valorization and potential agricultural reuse within a circular bioeconomy. This study evaluated four formulations (GC, T1, T2, and T3) produced in three biodigesters per formulation and anaerobically digested for 15 weeks. The three biodigesters within each formulation were pooled before preparation of the 5, 10, and 100% (v/v) bioassay dilution levels. Distilled water was retained as an external reference and excluded from factorial inference. Final formulation-level composite samples showed near-neutral pH and formulation-specific nutrient profiles; the measured nitrogen concentration in the analyzed liquid fraction was higher at the final sampling point in all four composite samples, whereas P, K, organic matter, and C/N ratio showed formulation-specific variations. Most final microbiological determinations were lower than their corresponding initial measurements, although variability remained in some T2 and T3 determinations. In Zea mays L. bioassays, germination percentage and germination rate showed significant formulation × dilution-level interactions ( p = 0.0065 and p = 0.015, respectively). Root length differed significantly by formulation ( p = 0.0145) and dilution level ( p = 0.0013), without a significant interaction. The germination index (GI), used as a phytotoxicity indicator, was evaluated descriptively; T2 maintained GI > 1 and comparatively high root length across all evaluated dilution levels, whereas T1 and T3 showed lower GI and root-length responses at 100%. Overall, responses were formulation- and dilution-level dependent, supporting soil-based validation of selected combinations before field recommendation. Because biodigesters were pooled at the formulation level before downstream analyses, these findings characterize the specific composite samples tested and do not represent independent reactor-level replication.