Wood Vinegar Safely Adjusts pH to Enhance Hydroponic Lettuce Yield, Photosynthesis, and Nutrient Uptake

Introduction

Hydroponics is an efficient and controlled method of growing vegetables, eliminating soil-related limitations while ensuring optimal nutrient supply. A critical aspect of hydroponic cultivation is maintaining the nutrient solution's pH within an optimal range. Traditionally, strong acids like nitric acid are used for pH adjustment, but these chemicals pose risks such as corrosion of equipment and potential harm to crops.

Wood vinegar, a byproduct of biomass pyrolysis, has gained attention as a natural alternative to synthetic acids. It contains organic compounds that can enhance plant growth and inhibit pathogens. However, limited research exists on its role in hydroponics. This study evaluates the effects of different wood vinegar concentrations on the growth, photosynthesis, and mineral absorption of hydroponic lettuce when used as a pH adjuster instead of nitric acid.

Experimental Design and Application

The experiment was conducted in a controlled greenhouse environment, using hydroponically grown Lactuca sativa (jade lettuce). The wood vinegar used had a pH of 3.3 and was refined to remove harmful residues.

Lettuce seedlings were transplanted into nutrient solutions containing three different concentrations of wood vinegar: 0.25 ml/L, 0.5 ml/L, and 1 ml/L, with a control group adjusted using nitric acid. Each treatment was replicated three times, with five plants per replicate. The pH of the solutions was monitored throughout the experiment.

Plant growth parameters, including fresh and dry weight, leaf area, and root development, were recorded. Photosynthesis rates were measured using a portable system, and nutrient absorption was assessed by analyzing water and mineral uptake over the growth cycle.

Key Findings

pH Stability

The 0.25 ml/L wood vinegar treatment maintained pH levels comparable to the control (nitric acid-adjusted solution).

Higher wood vinegar concentrations (0.5 ml/L and 1 ml/L) caused greater pH fluctuations.

Plant Growth

Lettuce grown with 1 ml/L wood vinegar showed significantly lower fresh weight, dry weight, and leaf area compared to other groups.

There were no significant differences in growth between the control and 0.25 ml/L wood vinegar treatments.

Nutrient and Water Absorption

The uptake of nitrate, potassium, and phosphate was lower in plants treated with 0.5 ml/L and 1 ml/L wood vinegar.

Ammonium absorption remained unchanged across all treatments.

The 0.25 ml/L wood vinegar treatment did not significantly affect nutrient uptake compared to the control.

Photosynthesis Rates

The 0.25 ml/L wood vinegar group had photosynthetic rates similar to the control.

Photosynthesis was reduced by 20% in the 0.5 ml/L treatment and by 40% in the 1 ml/L treatment, suggesting higher concentrations inhibited photosynthetic activity.

Implications and Conclusions

The study confirms that wood vinegar at 0.25 ml/L is a viable alternative to nitric acid for pH adjustment in hydroponic lettuce cultivation. It maintains nutrient solution stability, supports optimal growth, and does not negatively impact photosynthesis or nutrient uptake. However, higher concentrations (≥0.5 ml/L) hindered plant growth and nutrient absorption, likely due to excessive organic compounds affecting root uptake processes.

A notable advantage of using wood vinegar is its ability to reduce nitrate accumulation in lettuce, a health concern in hydroponic vegetables. By replacing nitric acid with wood vinegar at appropriate concentrations, growers can improve safety, sustainability, and environmental compatibility in hydroponic systems. Further research could explore refining wood vinegar formulations to optimize its effects on various crops.

Article based on: Effects of adding wood vinegar to nutrient solution on the growth, photosynthesis, and absorption of mineral elements of hydroponic lettuce