Critical examination of wood-based pyrolysis liquids as biostimulants for Nordic agriculture: an experimental study

This study evaluated whether wood-derived pyrolysis liquids can act as biostimulants for boreal crops. In a laboratory pre-experiment, low concentrations of willow-derived pyrolysis liquid promoted root growth of strawberry runners, whereas higher concentrations caused leaf lesions and inhibited rooting, indicating a hormetic response. In field trials in south-west Finland, birch-derived pyrolysis liquid was applied to spring wheat, field pea and spring oat at three dose levels and compared with an untreated control and two commercial biostimulants. Under the tested conditions, pyrolysis liquid did not significantly affect crop ground cover, plant height, grain yield or grain quality, and the commercial products did not outperform the untreated control. Because the tested liquids were not characterised in full batch-specific compositional detail, the observed responses could not be linked to individual compounds. The agronomic benefits of pyrolysis liquids under northern field conditions therefore remain unproven.