Wood Distillate Enables Seawater Use in Hydroponic Lettuce Production

Introduction

With the increasing demand for food production and the scarcity of arable land, hydroponic and aeroponic cultivation methods have gained considerable attention. These soilless systems allow for resource-efficient farming, minimizing water usage and dependency on synthetic fertilizers. This study explores an innovative approach to hydroponic agriculture by incorporating seawater (SW) at various concentrations as a nutrient solution base, with and without the addition of wood distillate (WD), a natural biostimulant derived from biomass pyrolysis.

Experimental Design and Application

The research assessed the impact of different concentrations of SW (0%, 3%, 6%, and 12%) and WD (0% and 0.2%) on lettuce (*Lactuca sativa* L.) growth in a controlled hydroponic environment. Lettuce seedlings were cultivated in modified Hoagland's nutrient solution, with varying SW concentrations to analyze their effects on growth parameters, photosynthesis efficiency, and nutrient uptake.

Key Findings

Effects of Seawater on Plant Growth

  • Low concentrations of SW (<6%) demonstrated potential as a sustainable water source, reducing freshwater dependency while maintaining adequate plant growth.
  • At 12% SW concentration, lettuce growth was significantly hindered, indicating that higher salinity levels imposed osmotic stress on plants.
  • The presence of SW influenced the uptake of various macro- and micronutrients, with notable increases in sodium (Na) and reductions in potassium (K) and magnesium (Mg).

Influence of Wood Distillate

  • WD addition did not significantly enhance plant biomass under lower SW concentrations but played a crucial role in increasing leaf ascorbic acid content.
  • Plants treated with WD exhibited higher concentrations of essential minerals such as calcium (Ca), magnesium (Mg), phosphorus (P), and potassium (K), suggesting an improvement in the nutritional quality of the lettuce.
  • The presence of WD appeared to mitigate some of the negative effects of high salinity by promoting the uptake of beneficial elements while reducing toxic accumulations.

Photosynthetic Efficiency and Biochemical Responses

  • Chlorophyll content was generally enhanced with WD, except at the highest SW concentration (12%), where growth inhibition was evident.
  • Photosynthetic parameters (Fv/Fm and PIabs) initially declined but later improved in WD-treated plants, indicating a potential eustress effect that ultimately benefited plant metabolism.
  • Eustress refers to a beneficial form of stress that, rather than harming the plant, stimulates adaptation and resilience.
  • The increase in leaf ascorbic acid levels in WD-treated plants suggests a strengthened antioxidant defense system, which may contribute to enhanced stress tolerance.

Implications

  • Low levels of seawater can be incorporated into hydroponic solutions without compromising plant health, reducing freshwater consumption.
  • Wood distillate enhances the nutritional quality of lettuce by increasing mineral content and antioxidant levels.
  • Future research should further explore optimal concentrations and long-term effects to refine these techniques for large-scale applications.

By leveraging these natural resources, hydroponic farmers can move towards more resilient and resource-efficient cultivation methods.

Article based on: Evaluating Seawater and Wood Distillate for Sustainable Hydroponic Cultivation