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Bioelectromagnetism

 

FIGURE 2.9 Plant growth experiments (From Shibusawa, 1963.)

electrode no more than 10 cm from the tip of the plant, allowing the variation of the feld strength. When

the seedlings were continuously exposed to the electric feld, the tips of the seedlings turned brown,

as if they were burning, which Murr observed to be the same as a situation of mineral defciency. Te

relationship between the plant’s response to the electric feld and corona current was then examined.

Murr classifed the efects on the plants according to the range of currents fowing in them. Te results

showed that currents fowing through the plants above 10⁻⁵ A resulted in damage to the plant and leaves;

10⁻⁸~10⁻⁶ A resulted in leaf damage and negative efects of reduced dry weight; 10⁻¹⁵~10⁻⁹ A resulted in

positive efects such as growth promotion and increased dry weight; and below 10⁻¹⁶ A had no efect

(Murr, 1966). Francis Xavier Hart, a professor at the University of the South, Sewanee, Tennessee, USA,

believed that the efects were due to the water loss from the leaf tips when corona current fowed caused

by the high electric felds (Hart and Schottenfeld, 1979).

In the next steps, more interest in other than static electric feld, started as if had been shown about the

efects of air ions on plant growth (Bachman and Reichmanis, 1973; Krueger et al., 1962). Krueger et al.

showed that air ions rather than electric felds were important for plant growth. Albert Paul Krueger

(1902–1982) was a well-known bacteriologist of air ions and professor at the University of California,

apart from the application to electro-culture, a few studies on its benefcial efects appeared in the 1960s

and 1980s (Kotaka and Kruger, 1968; Pohl and Todd, 1981; Yamaguchi, 1983). Tey were conducted to

investigate the efects of air ions on plant growth and production with the presence of the static electric

felds. In order to put Kruger’s results into practice, Herbert Ackland Pohl (1916–1986), a professor at the

Oklahoma State University, observed growth efects in Persian violets as well as in seedling geraniums

in green houses with high concentrations of negative ions (4 pA/cm²) and showed that exposure to these

ions resulted in longer grasses, earlier fowering time and increased fowering numbers. Te experi­

ment was conducted using an air ion generator with needle electrodes (Pohl and Todd, 1981). Frank M.

Yamaguchi from the Research & Development, General Agriponics, Inc., USA, conducted hydroponic

cultivation experiments of tomato plants (Lycopersion esculentum P. Miller) under high concentration

of negative ions in a green house, using a negative ion generator with corona discharge. He reported

that the time from sowing to harvest was shortened and that the yield was increased. For plant growth,