Abstract
Effects of zeta potential of microbubbles on plant growth of Japanese mustard spinach (Brassica rapa var. perviridis) in soilless culture were evaluated. Experiment (i) dealt with two kinds of concentrations of nutrient solution (10 or 100% concentration) and three kinds of pH (4.5, 5.5 and 6.5). Microbubbles were adopted only in the 10% concentration plot. Experiment (ii) dealt with the above two concentrations of nutrient solution with and without microbubbles at pH 4.5. Zeta potential at pH 6.5 was larger than that at pH 4.5. The experiment (i) showed that the growths of the plants in pH 4.5 plot with microbubble were inhibited, whereas the plants in pH 6.5 plot with microbubble grew better than those in other plots. In the experiment (ii), the inhibition at pH 4.5 due to microbubbles appeared regardless of the concentration of solution. Multi-element determination revealed that absorption of K or Ca was enhanced at pH 6.5 and reduced at pH4.5 due to microbubble. These results indicated that microbubble treatment in low-concentration nutrient solution could promote mineral uptake by roots, which results in enhancement of plant growth, as long as zeta potential of microbubbles is adequately large.
