Introduction
In an era of increasing environmental consciousness and sustainable agricultural practices, researchers are seeking alternatives to synthetic chemicals that often harm human health, reduce biodiversity, and pollute the environment. Pyroligneous acid (PA), also known as wood vinegar or wood distillate, has emerged as a promising solution. A comprehensive review conducted by researchers Jens Leifeld and Iva Walz from Agroscope, Switzerland, has revealed the substantial potential of pyroligneous acid in boosting crop yields and enhancing soil health.
Pyroligneous acid is a by-product of biomass pyrolysis and biochar production, containing a complex mixture of organic acids, phenols, and other compounds. This natural agricultural product does not pollute the environment and has no toxic effects on humans or animals, making it an ideal candidate for sustainable agriculture.
Experimental Design and Application
The researchers analyzed 65 peer-reviewed studies comprising 171 yield and 123 plant biomass data sets, covering 33 different crops across 6 plant groups. The analysis examined how PA concentration, application method, and frequency affected crop yield and plant biomass.
PA application methods in the studies included:
- Foliar application: Spraying PA solution directly onto plant leaves
- Soil irrigation: Applying PA solution to the soil around plants
- Seed priming: Treating seeds with PA before planting
- Nutritional solution: Adding PA to hydroponic growing solutions
The concentrations of PA varied widely across studies, ranging from as low as 0.1% to as high as 100% (the latter used exclusively for herbicidal purposes). Application rates were typically measured either as a concentration percentage or in tonnes per hectare (t/ha) for soil applications.
Key Findings
The results of the review were remarkable. Across all studies, pyroligneous acid showed a clear and significant positive effect on plant growth, with an average 25% increase in plant biomass and 21% increase in crop yield. The highest effectiveness was observed at the optimal application rate, with yields increasing by an average of 31%.
The relationship between PA concentration and yield was non-linear. Low concentrations (0.1-1%) produced substantial benefits, with the optimal range identified between 0.5-1% concentration or less than 0.1 t/ha application rate. However, concentrations above 6% began limiting positive effects, and concentrations above 10% could actually harm plants and were sometimes used for herbicidal purposes.
Different application methods showed varying optimal concentrations:
- Foliar application: Maximal effects at approximately 0.6% concentration
- Soil irrigation: Similar pattern but with greater variability in results
- Seed priming and nutritional solutions: Showed high sensitivity to concentration, with positive effects at very low concentrations (<0.3%)
Particularly noteworthy was PA's effectiveness under stressful growing conditions. Seven studies examined PA's ability to promote stress tolerance against high salt concentrations, drought, and pathogen infections. In all seven studies, plants under stress showed significantly greater yield increases with PA application than unstressed plants. This suggests PA application is particularly valuable in suboptimal growing conditions, where it can substantially reduce yield losses.
The review also investigated soil parameters. Soil organic matter (SOM) content showed a small but significant positive response (9% increase on average) to PA application. Dissolved organic carbon (DOC) in soil similarly increased by about 9%.
Implications
This comprehensive review offers compelling evidence that pyroligneous acid is an effective, environmentally friendly alternative to synthetic agricultural chemicals. Its beneficial effects on plant growth and yield were consistent across different plant groups and growing conditions, with particularly strong benefits for plants under stress.
The optimal application concentration of 0.5-1% maximizes benefits without adverse effects. The research suggests PA's effectiveness stems from multiple mechanisms, including increased nutrient availability, suppression of pathogens, and stimulation of root development and plant defense systems.
For farmers and agricultural practitioners, these findings suggest several practical applications: using low-concentration PA as a foliar spray to enhance crop yield, applying PA to crops under stress conditions to minimize yield losses, using PA as a seed treatment at very low concentrations, and potentially using PA as part of a soil amendment strategy.
The researchers note, however, that most studies were short-term experiments of only 1-2 growing seasons. There is a significant research gap regarding the long-term effects of PA application, particularly on soil parameters. Despite these limitations, the review strongly encourages further research on pyroligneous acid for sustainable agriculture.
Article based on: Leifeld, J.; Walz, I. Pyroligneous Acid Effects on Crop Yield and Soil Organic Matter in Agriculture—A Review. Agronomy 2025, 15, 927.