Pyroligneous acid (PA) or wood vinegar, a co-product of biomass pyrolysis, is thought to be beneficial for plant productivity and soils, with the potential to reduce otherwise harmful agrochemicals. Here, we review the evidence for the use of PA on plant growth and soil health parameters. The analysis includes 65 peer-reviewed studies with 171 (yield) and 123 (plant biomass) data sets, covering 33 different crops belonging to 6 plant groups. Significant positive, non-linear relationships between PA concentration, yield, and plant biomass were found at concentrations as low as 0.1%, with the optimum at around 0.5–1% and overall positive effects up to 6–11% (depending on the application type), but yield declines above these concentrations, suggesting herbicidal effects. Across the whole data set, yield and biomass increase by an average of 21% and 25%, respectively, and by an average of 31% at the optimum rate. The positive effect of PA is most pronounced for plant growth under sub-optimal conditions (salt, drought, and pathogens), while responses did not differ between plant groups. Soil organic matter content shows a small but significant positive response to PA application, but the amount of data is very small compared to the plant parameters. The major shortcomings identified include inconsistent measures of applied PA (amount and composition) and the short duration of experiments of typically only 1–2 growing seasons, which prevents analysis of long-term PA effects. Overall, the results of this review encourage further research on PA for sustainable agriculture.
