Influence of a plasma-treated nutrient solution containing 2,4-dichlorobenzoic acid on the growth of cucumber in a hydroponic system

Allelochemicals are organic compounds exuded from the roots of plants, which have autotoxic effects on plant growth. In this study, the decomposition of 2,4-dichlorobenzoic acid (DCBA), an allelochemical of cucumber, by plasma generated in an air bubble in solution is examined, and the influence of plasma treatment of the solution on cucumber growth in a hydroponics system is investigated. Air gas is injected into water through a vertically positioned glass tube, into which a high-voltage wire electrode is placed to generate plasma. The concentration of DCBA decreases and the concentration of chloride ion produced by the dichlorination of DCBA increases with increasing discharge treatment time. Consequently, most DCBA has decomposed after 24 h of treatment. The discharge-treated solution is used as a nutrient solution for cultivating cucumber plants in a rockwool hydroponic system. The results show that the growth of most plants is inhibited by adding DCBA, as well as by the decrease in pH during discharge treatment; in contrast, plants subjected to discharge treatment with pH adjustment grow healthily.