Hydroponic farming is a sustainable method for growing crops without soil, but maintaining optimal nutrient levels is essential for plant health and yield. Although the hydroponic system is a more controlled environment than soil, plant protection remains crucial. Currently, several natural treatments are adopted in hydroponic farming to boost the plants' immune systems and mitigate stress and nutrient imbalances without relying on harmful chemicals. Wood vinegar, a natural byproduct of biomass pyrolysis, has gained attention for its potential to enhance plant growth and stimulate plant defenses. With an estimated 200 billion tons of lignocellulosic biomass produced annually by agriculture and forestry worldwide, the utilization of such byproducts could play a key role in sustainable agricultural practices.
This study investigates the impact of wood vinegar on hydroponic lettuce (Lactuca sativa) and basil (Ocimum basilicum) under nutrient stress, aiming to explore the possibility of applying lower quantities of chemically synthesized nutrients and achieving more sustainable production. Several separate and independent experiments were conducted for lettuce and basil, with each species undergoing four treatments. The control groups included one with 100% nutrient solution and another with a nutrient-deficient solution (i.e. 20%). Two additional treatments combined the 20% nutrient solution with wood vinegar at 0.3% and 0.1% dilutions of an extract that had a total phenolic content of 2,3 mg/mL. Wood vinegar was applied weekly. Growth parameters were measured to assess its potential benefits.
The results showed species-dependent and concentration-sensitive effects. In basil, the 0,1% treatment slightly increased the plant height and leaf number compared to the 20% control, suggesting a mild growth-promoting effect. However, the 0.3% concentration was shown to be phytotoxic and reduced plant growth. In lettuce, the 0.3% treatment led to severe phytotoxicity, significantly stunting growth. The 0.1% treatment initially performed similarly to the 20% control but, by the sixth week, caused root blackening and decay, leading to a marked decline in plant health.
These findings suggest that the effects of wood vinegar depend on both the concentration and the plant species. While a lower concentration showed slight benefits for basil, it ultimately harmed lettuce by damaging its root health. Higher concentrations were phytotoxic to both crops. These results indicate that while wood vinegar may have potential as a plant growth enhancer, concentration management is crucial. Further research should explore its long-term impact on root health and its interactions with hydroponic nutrient solutions to determine its viability in nutrient-limited hydroponic systems.