Pyroligneous Acid Increases Grape Yield and Quality
Introduction
In an era of increasing environmental consciousness and the pursuit of sustainable agricultural practices, researchers are exploring alternatives to synthetic agrochemicals that often harm human health, reduce biodiversity, and pollute the environment. A promising solution has emerged in the form of pyroligneous acid (PA), a natural byproduct derived from the pyrolysis of plant biomass. A recent study conducted by researchers from Dalhousie University in Canada has revealed the significant potential of pyroligneous acid in enhancing grape (Vitis vinifera) production, a crop of immense economic value worldwide.
Pyroligneous acid, also known as wood vinegar or wood distillate, is a complex mixture containing water and over 200 water-soluble compounds including phenolics, alcohols, organic acids, sugar derivatives, and esters. 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 viticulture.
Experimental Design and Application
The researchers investigated the effects of pyroligneous acid at different concentrations (0%, 4%, 8%, and 12%) and application frequencies (14-, 21-, and 28-day intervals) on grapevines (cv. KWAD7-1). The experiment was conducted in an established vineyard in Jost Vineyard, Malagash, Nova Scotia, Canada, during the 2022 and 2023 growing seasons.
The PA used in this experiment was produced from white pine (Pinus strobus) biomass using a fast pyrolysis process. Dilutions were prepared by using raw PA (100%) and water to obtain the various concentrations. In the first year, the researchers applied different concentrations (0%, 4%, 8%, and 12%) at a 21-day interval, while in the second year, they focused on the 4% concentration applied at different intervals (14, 21, and 28 days).
Application of the PA solution began at the bud break stage, with each plant receiving 0.1 liter of solution applied as a foliar spray directly to the leaves of the plants. This is a key detail, as the researchers specifically mention applying the PA "to the leaves of the plants" rather than to the soil. As the plants progressed to vegetative and reproductive stages, the application volume increased to 0.3 and 0.4 liters per plant, respectively. Throughout the study, the plants relied on rainfall for water, with weed control and pruning performed as needed.
Key Findings
The results of the study were remarkable and were conducted over two separate experiments. In the first experiment comparing different PA concentrations (all applied at a 21-day interval), the application of 4% and 8% PA showed a nonsignificant increase in berry yield (fresh weight of grape clusters) of about 0.37- and 0.18-fold, respectively, compared to the control (0% PA). Conversely, the 12% PA treatment reduced the berry yield by approximately 0.03-fold compared to the control. This suggests that lower concentrations of PA are more effective for enhancing grape production, though the increases were not statistically significant.
In the second experiment, when using a fixed concentration of 4% PA, the researchers found that the application frequency significantly affected plant performance. The 21-day interval application of 4% PA significantly outperformed both the 14-day and 28-day intervals in terms of fruit fresh weight, juice weight, juice volume, and press weight. According to Figure 4 in the study, the 21-day interval treatment enhanced fruit fresh weight by approximately 40-45% compared to the 14-day interval and by about 30% compared to the 28-day interval. Similar improvements were seen in juice weight, juice volume, and press weight.
Perhaps most interestingly, PA application altered the biochemical composition of grape leaves, pomace, and juice. The 4% PA treatment significantly improved total carotenoids (0.34-fold), total phenolics (0.26-fold), and flavonoids (0.26-fold) in grape juice compared to the control. These compounds are important for the nutritional and health properties of grapes, which have been linked to the prevention of various chronic diseases.
Implications
This research offers compelling evidence for pyroligneous acid as an effective, environmentally friendly alternative to synthetic agrochemicals for enhancing grape production and quality. The study demonstrates that PA not only potentially increases yield but also improves fruit quality and stimulates the accumulation of beneficial biochemical compounds.
Particularly noteworthy is the finding that lower concentrations of PA (4% and 8%) were more effective than the highest concentration (12%), suggesting that there is an optimal application rate beyond which the benefits diminish. Additionally, the 21-day application interval proved most effective for enhancing vine growth, yield, and juice quality parameters.
For grape farmers, these findings present an opportunity to reduce their reliance on synthetic inputs while potentially improving the yield and quality of their produce. The relatively low concentration (4%) and extended application interval (21 days) observed to be most effective in this study suggest that farmers could reduce their input costs while maximizing production and quality.
This sustainable approach to grape cultivation aligns with the growing consumer demand for environmentally friendly agricultural practices and could contribute to reducing the environmental impact of viticulture. However, the researchers suggest that further studies should be conducted to evaluate the effect of PA on metabolites in grape wine, which represents the primary use of grapes globally.