Popular Science Monthly/Volume 17/September 1880/Electricity and Agriculture
By Dr. PAGET HIGGS.
M. L. GRANDEAU, Professor in the School of Forestry, of France, was the first to point out definitely the influence of atmospheric electricity on the nutrition of vegetation.
His labors are described in the "Annales de Chimie et de Physique," for February, 1879, and he there gives the results of experiments carried out in 1876-’78.
These experiments are little known, but are of the highest importance to agriculture. As they bear upon similar experiments under-taken by the writer, a résumé is merited. M. Grandeau was led, from the common observation that the underwood in a dense forest disappears, to consider the influence of trees on the vegetation beneath them. Studying the causes generally assigned in explanation of this natural phenomenon, such as diminution of light, and the influence of the green light reflected by the trees, these appeared to him insufficient, and he concluded that the loss of electricity, due to the trees acting as an electrical screen, was the cause of the retarded growth—a theory that his experiments, as well as those of M. Mascart, ultimately confirmed.
The experiments consisted in placing plants under similar conditions of soil, light, and water, but covering one plant with a cage of iron-wire netting of very large mesh, the netting acting as a faradic cage, or somewhat as a lightning-conductor; the wires of the netting were one fiftieth of an inch in diameter, and the mesh six inches by four. Illustrative of the effect of this arrangement, the case may be cited of two tobacco-plants, otherwise under similar conditions:
Chemical analysis showed defective nutrition in the plant placed under the cage, and withdrawn from electric influence. These experiments were greatly extended, and trials were made as to the relation of electrical effect and nitrification of the soil, and the assimilation of the ammonia of the atmosphere by plants. ,The results are summed up by M. Grandeau as follows:
"That trees withdraw, for their own profit, electricity from the atmosphere, and insulate, as completely as a metallic cage, the plants they cover. Insulation produced by a high tree can extend to the extreme limits of its foliage. A plant withdrawn from the influence of atmospheric electricity is subject to marked retardation in its development, so that the quantity of living substance in insulated vegetation is from thirty to fifty per cent, less than the production in free air.
"The transformation of chlorophyllic protoplasm into glucose, etc., appears particularly influenced by atmospheric electricity.
"Flowering and fruit-bearing are subject equally to modification. Electricity does not appear to favor the direct combination of the nitrogen of the air with oxygen, nor with the hydrocarbons of the soil; but it exercises a remarkable influence on the nitrification of the nitrogenized matters of the soil by the intervention of the plant as an electrical conductor. Atmospheric electricity is, therefore, a preponderating factor in vegetable production."
These considerations induced the writer to carry out a series of experiments to ascertain the effect on vegetable development of a surcharge of electricity.
It would appear, from the primary consideration of intensified electrical conditions existing in tropical climates, that the more rapid growth of tropical vegetation might be due to higher electrical force. To the resident in tropical climes such a proposition would be beyond the limits of theory, because of the constant observation of the great development in vegetation during and immediately after a thunderstorm.
The experiments undertaken by the writer gave results that leave no doubt that the growth of vegetation may be enhanced twenty-five to fifty per cent, by the judicious application of electricity.
These experiments consisted in placing upon two marble slabs, one of which was carefully insulated, ten plants of the kind under trial. On the insulated slab was raised an iron structure with depending points, arranged to discharge into the atmosphere surrounding the plants the electricity produced by an induction-machine at an estimated potential of about four thousand to five thousand volts. This arrangement and difference of electrical condition, other conditions being the same, were maintained day and night for eight months, resulting in unmistakable increase in the development of the surcharged plants. The practical application of electricity to the hastening of the development of vegetation is easy. Above the plants or among them may be placed a number of metallic points on a framework insulated from the earth. Wires carried by small balloons—India rubber or collodion bladders filled with gas—to a considerable elevation would collect sufficient of the electricity of the atmosphere, which would be imparted to the points, and these would discharge slowly to the earth, saturating the atmosphere in the neighborhood of the plants. The cost of such an arrangement would be small, and that great advantages are to be obtained from it is undoubted.