ELECTRICAL STIMULATION OF CROPS.

New Zealand Journal of Agriculture, Volume XV, Issue 4, 20 October 1917, Page 185

ELECTRICAL STIMULATION OF CROPS.

L. BIRKS,

B.Sc., M.1.E.E., M.1.C.E., AND O’D. DAVIS.

Among the many uses to which electricity is now being put perhaps one of the most interesting and far-reaching is its ■ application to the stimulation of plant-growth. In view of the increasing world foodshortage at the present time, due to various war influences, any means whereby stimulation of crops can be effected becomes of national importance.

The first experiments worthy of note in the direction of this new science of electro-culture were started in England in 1911 by Professors Priestly and Jorgensen and Miss Dudgeon. Up to 1915 no very conclusive results were obtained, but in that year considerable improvements were effected in the methods employed, giving definite results of commercial importance. As indicating the degree of success achieved, it was found that increases up to 50 per cent, over the normal crop were obtained with oats on Miss Dudgeon’s land, while a crop of potatoes treated electrically yielded 40 tons 6J- cwt. from 8 acres, as against 34 tons 3| cwt. from soil not so treated, an increase of 15 per cent. Moreover, the “ electrical ” crop was ready for lifting a week earlier, and the class of potato was superior in every way to that of the untreated crop. ; Even more striking results were obtained last year at Miss Dudgeon’s farm at Dumfries, where an electrified area of 1 acre produced no less than 62 bushels of oats and 4,924 lb. of straw, as against 42 bushels of oats and 2,619 lb. of straw on the normal crop, an increase of 49 per .cent, in oats and 88 per cent, in straw.

These are only a few of the' more important results obtained. Many investigators are now in the field, and their work is being greatly stimulated by the exigencies of the war. The English Board of Agriculture is turning serious attention to the problem of electroculture, and many experts are agreed that by its aid the people in Britain ■ will be made far more . independent of imported food, and this without calling on the already scanty reserves of man-power.

NEW ZEALAND CONDITIONS AND LOCAL EXPERIMENTS

In consequence of the development of large hydro-electric-power supplies, enabling electricity to be used freely and at a very cheap

rate, New Zealand is in a particularly favourable position to continue the investigations already carried out, and so help in the solving of what is now a problem of national interest. The Province of Canterbury, with its three million acres of farming-country and its agricultural institutions, together with its already well-developed hydro-electric-power supply, offers every facility for the carrying-out of electro-culture on a large scale.

Preliminary experiments have already been made at Christchurch in connection with the Lake Coleridge power-supply, with most encouraging results. More extensive investigations are to be made this year, and it is anticipated that as a result the commercial possibilities of electro-culture in New Zealand will be still further demonstrated. The following description of last season’s experiments will serve to indicate two of the directions in which the practical applications of electricity have met with considerable success.

The first experiment was carried out in a glasshouse belonging to Mr. E. Lunt, of Spreydon. The house is 80 ft. by 30 ft., and is provided with ’ the usual means of heating by steam-pipes. In August last year 1,400 tomato-plants were set out in this house. A week after planting one of the steam-pipes burst, crippling the whole heating installation, and of course depriving the plants of any protection from the severe frosts. Eight , days elapsed before the heating-apparatus could be got into working-order, and during that time a sharp frost so damaged the plants that it was considered unlikely that they would , mature at all. Ten days after the fracture of the steam-pipe, the house was provided with an electrical installation consisting of fifteen 100 candle-power nitrogen-filled lamps with frosted globes. The lamps, provided each with a in. enamellediron shade, were hung at a height of 2 ft. from the ground, the area under influence of each lamp being 100 square feet. The current was switched on each night at 9 p.m., and off again the following morning at 5 a.m. The restored steam-heating was used in conjunction with the electric lighting for one month only ; after that it was discontinued altogether. The plants rapidly recovered from their frost-bite and made vigorous growth. As ' the height of the plants increased the lamps were raised accordingly, until the tops of the plants completely, enveloped them. As a result of the electrical treatment the plants not only entirely recovered from their serious setback, but the crop was a very heavy one and matured relatively earlier than that in another house in which steam-heating had been used during the whole season. Owing to the breakdown of the heating-system it was not possible to obtain a direct comparison between two crops under exactly similar conditions except for the use of electric light, but there was sufficient evidence to

establish the fact that the electrical treatment resulted in a definite stimulation of growth with a proportionate increase in the yield.

A further experiment, which had for its object the investigation of the possibilities- of frost-prevention in orchards, was made in the orchard of Mr. E. C. Farr, at Fendalton. Here twenty-four trees, arranged in three rows of eight, were chosen for the experiment. One row was of pear-trees, and the other two of mixed apples Worcester Pearmain, Jonathan, and Stunner. In the centre of each tree, well down towards the fork, was suspended a . 250-watt radiator lamp. The lamps were- switched on only on those nights when it was' thought probable a frost would occur, and were left on all night. The first frost < experienced during the season followed a very wet day. In the morning it was found that the electrically heated .trees were quite dry on the inner branches, parts of the outside of the tree being frosted. The radius of action of the heat from the lamps was shown to be approximately 1 ft. below the lamp, 4 ft. above, and 3 ft. all round measured in a horizontal plane. Two hard frosts occurred during the season, besides many less severe ones. The heating of the trees had apparently- no effect in the case of the pears, but the crop of apples on the “electrical” trees, in addition to being a heavier one than on the others, was ready for picking fully a fortnight earlier. ' The significance of the results- of this experiment will be realized more fully when it is remembered that the late frosts which so frequently occur are responsible for much damage to the fruit crops, resulting frequently in a . great shortage of marketable fruit and consequent inflated prices. The application of electricity for frost-prevention , in orchards, coupled with stimulation of growth of the fruit, should prove a matter of considerable commercial importance.

METHODS OF ELECTRICAL APPLICATION. —COMMERCIAL RETURNS

Electricity is applicable to the stimulation of plant-growth, by ifour /distinct methods—(i) The influence of heat; (2) the influence of light (3) the stimulation by “ionization” of the atmosphere by means .of , high-pressure electrical discharge ; (4) the stimulation ;of the roots by an electric current at low pressure through the soil.

< These, together with the regulation of the humidity, of the atmosphere by electric spray-pumping, give every possible means of controlling plant-growth and in much more flexible form than is :available under natural conditions. With electric power we have thus the means at command of producing any season at will at any time of the year, and at a very moderate cost both in capital and maintenance. From field agriculture and horticulture, a large increase in return is possible, but it is from intensive greenhouse culture that

the largest increase is available. The capital outlay in buildings alone per acre of glass-enclosed area is very high, probably exceeding £5,000 per acre, and the interest and depreciation charges at, say, 8 per cent, thus cost £4OO per acre per year. In comparison with these figures the cost of a complete electrical installation for reproducing any season at any time of the year will be small— 10 to 20 per cent, of the actual present capital, and interest and depreciation charge on the glasshouse. With such an equipment the glasshouse need not be out of service for a single week in the year. - At least two, probably three, “ springs ” could be reproduced annually at any time of the year, and two or three crops taken off, each much larger than the normal annual crop produced by the natural effects of the sun and stimulated only with 'artificial heat. Moreover, the market price of tomatoes and similar crops produced throughout the winter would (under existing relations of 'supply to demand) be four to six times that of the summer crop. It is thus by no means unreasonable to look to electrical stimulation of glasshouse crops to produce on the same basis ten to twenty times the actual commercial return now obtained from the same houses, after allowing for all the actual costs of such stimulation.

Nor are the electrical methods, very complicated, difficult, or expensive. As far as temperature-regulation is concerned, an automatic thermostat will maintain any temperature required up to roo° F. accurately to within a couple of degrees, throughout, the day and night and throughout the year. Similar thermostats are already in regular service for fire-alarm services, and have been well developed for this purpose. The actual temperature to be maintained can be varied as required by a few turns of a screw.

To reproduce the effects of sunlight either ordinary incandescent lamps, or preferably mercury-vapour' or other special lamps richer in the ultra-violet rays, may be used, the sunlight itself being relied on in the daytime. By this means the action of the chlorophyll of the leaves in fixing the carbon dioxide from the atmosphere can be continued for twenty-four hours per day, practically doubling the summer rate of growth and enabling the same rate to be continued through the winter as well.

The regulation of humidity will be effected by sprays operated from a small electric pump. The automatic control of the humidity is possible, but it would probably be cheaper to regulate it accurately to the degree required (say, twice a day) by hand, and it would thus be maintained fairly close , to the required point throughout the twenty-four hours.

The further stimulation of growth by means of high- pressure discharge or ionization of the atmosphere, and of the roots by galvanic

currents, will probably yield even more prolific results in practice, judging by the experiments carried out in England and America, but these results cannot be so definitely forecast as in the case of stimulation by the correct degrees of heat, light, and humidity.

Cheap electric power is, of course, a sine qua non. The Lake Coleridge scale of charges offers electricity at £1 per kilowatt per month for unrestricted use Lb., |d. per unit if it can be used for the full 720 hours per month j' and 4s. per kilowatt per month if restricted to the hours of 9 p.m. to 8 a.m. —Lb.; yd. per. unit if it can be used for the full 330 hours per month. In practice the supply cannot be used for the full time as assumed above, but even if it can only be used for half time the cost per unit is only |d. to |d., which is still very low. Most of the British and American experiments are worked out on the basis of electricity at 2d. to sd. per unit, and even at these prices the electrical stimulation of crops is found to pay well. ' ’

There is thus a very large field for development hitherto practically untouched, and one which the war conditions render particularly important.