The effect of electric current on certain crop plants
Is Version Of
In this investigation the primary object has been to study the possible effect of weak electric currents, similar to those existing in nature, upon plant growth and certain phases of the environment. The experiments have been of two types: (1) Those using the earth-air currents collected and discharged by means of elevated metal brushes, and (2) those using currents generated as the result of differences in potential between buried, aerially connected, copper and zinc electrodes, sometimes augmented by dry cells placed in the circuits. In both types the currents developed have been applied to the root areas of the plants.
1. Currents obtained by means of. the installation of elevated metal brushes connected with buried wires trans versing the root areas of field crops apparently had little effect on yields. Yearly averages show a variation from the controls with corn of -2.78 to +4.51 percent; with soybeans of +0.29 to +3.16 percent; with turnips of -3.95 to +7.03 percent; with chard of +3.39 to +9.08 percent; with beets of + 5.55 to + 11.05 percent; with string beans of +1.82 to +3.91 percent.
2. Currents passing through the elevated metal brushes during fair weather changed direction frequently and were of the order of from 5.0x10-10 amperes to 1.0x10-9 amperes. During unsettled weather the currents varied greatly, both in direction and magnitude, the highest value being of the order of 200x10-9 amperes.
3. The intensities of the currents measured in the soil and along the buried conductor at various distances from one of the elevated 'brushes seemed to bear no relation to the intensities measured at the point where the conductor entered the soil.
4. The application of currents ranging in intensity from 7,000 to 20,000 volts to the roots of oats in greenhouse fiats did not produce significant variations in yields of grain and straw. The yields of the treated lots varied both above and below the average of the controls, and none yielded more than the higher control. The high voltage currents were applied for 15 minutes each day throughout the growing period.
5. The greenhouse treatments in which an electrode of copper and one of zinc were buried at opposite ends of the soil area to be treated, and connected aerially by copper wire, produced significant increases in yields of oats the first year of the experiment. Currents measured were of the order of from 0.5 to 1.5 milliamperes. The second year of the experiment, the grain and straw yields were not increased by treatment with electric current, while root yields were significantly decreased. For this test one or two dry cells were included in the circuit for each treated lot, and current intensities ranged as high as 4.0 milliamperes.
6. In the field trials with oats the copper-zinc electrodes combination, with dry cells included in the circuits, provided current intensities ranging from 2.0 to 55.0 milliamperes but failed to affect the yields significantly.
7. In the comparisons using the copper-zinc electrodes combination, the percentage of total nitrogen of oats apparently was not affected by treatment with electric current.
8. With the exception of the determinations made in connection with the field tests, a rather definite relationship between electrical treatment and numbers of soil microorganisms was observed throughout the series of experiments. In the 1932 greenhouse experiment, a comparison of 24 samples showed increases for the electrically treated lots of 14 to 123 percent and of 15 to 23 percent for 20 samples in 1933. Further proof was provided by the carbon dioxide determinations, a weak current of 0.1 milliampere producing appreciable increases in amounts of carbon dioxide formed and a relatively strong current of 10 to 15 milliamperes resulting in pronounced decreases.