Popular Science Monthly/Volume 67/December 1905/Economy in Irrigation
|ECONOMY IN IRRIGATION.|
DESERT BOTANICAL LABORATORY, TUCSON, ARIZ.
THE annual reports of the Reclamation Service of the United States and current numbers of Forestry and Irrigation embody, as is well known, a large amount of information of great general interest and at the same time of vital concern to that half of the country lying west of the Missouri River. What chiefly impresses the casual reader is the fact that a body of trained engineers, under government employ, in Arizona, California, Colorado, North and South Dakota, Idaho, Kansas, Montana, Nevada, Oklahoma, Oregon, Utah, Washington and Wyoming, are engaged in the great work of opening arid America to cultivation, and that irrigation is the chief agency by which this is being accomplished. Topographic parties are engaged in mapping and in sinking test pits, careful surveys have been made, land and water relations in different states have been thoroughly studied, and methods of raising, storing and distributing water are being worked out, both theoretically and practically, on a scale and in a manner new to the world. With a sympathetic popular interest awakened, the favorable attitude of the general government, and the high character and attainments of the experts who are engaged in solving the problems involved, the Reclamation Service has made noteworthy progress in a work that for scientific interest combined with economic importance is perhaps second to none ever attempted by any government.
As is natural in a region where water is the one great essential, and of which it would seem that there can never be enough, the first thought apparently in all cases has been directed towards securing a sufficient and permanent supply, while economy of use has not, thus far, been embodied in any satisfactory general system. Years ago Professor Hilgard, of the California Agricultural Experiment Station, urged the necessity of more perfect utilization of irrigation water by putting it where it would do the most good, close to the stem of the plant or trunk of the tree, and letting it soak downward so as to form a moist path for the roots to follow to the greatest possible depth. More recently Dr. Elwood Mead, chief of irrigation and drainage investigations, U. S. Department of Agriculture, has given measurements showing the great loss by seepage and evaporation from irrigation canals, and has discussed methods by which the water-supply might be more economically utilized. After giving tables which show in a striking manner the extent of losses by methods still in vogue, the author concludes: "A comparison of the duties secured. . . leads to the belief that it will be possible through improved methods to double the average duty now obtained, so that the quantity now required for one acre will serve to irrigate two. If this can be accomplished it will relieve the scarcity under many canals, put an end to many controversies growing out of such scarcity, lessen the expense per acre for water and immensely increase the productive and taxable resources of the arid states."
In various parts of the old world, where much valuable land has been reclaimed by irrigation, water is distributed in such a way as to secure the best practicable results. At Biskra, Algeria, for example, where the famous Deglet Noor date is grown and the supply of water is limited, an excavation is made around the base of each tree, and this is filled with water, thus greatly lessening the loss that would otherwise result from evaporation, At Bassorah, on the river separating Persia from Arabia, the extensive date plantations are watered by means of a system of canals which are flooded with each high tide, dams of mud being built with the hollow trunks of palms run through them, which permit the water forced into the canals by the rising tide to flow away slowly. Thus, by taking advantage of favorable natural conditions, an ideal system of combined irrigation and drainage is effected at a minimum' of expense.
In close agreement with the estimates of Dr. Mead, observations of Seedlings of Palo Verde. Number 3 had as much water as number 4, but it was not economically applied. the writer have shown that plants supplied with water below the surface of the ground have made a vigorous growth on a little more than one half the quantity of water that would be required if applied at the surface. To report a single rather striking case—the plants shown in the accompanying figure are photographs of seedlings of palo verde (Parkinsonia, two species) which, with some other desert plants, were under investigation. They are here shown as they appeared August 10, after being supplied with measured quantities of water since June 12. During this period numbers 1 and 2 each received 71 ounces of water, while numbers 3 and 4 each received but 39 ounces, or 55 per cent, as much as 1 and 2. Numbers 1 and 3 received at the surface all the water given them, while 2 and 4 were subirrigated by means of a three-fourth-inch glass tube which extended some three inches vertically into the soil.
These plants started all alike, and in every other respect except water-supply had an even chance, so that the difference in their development, as seen two months after the seeds were sown, is highly instructive. The thing which at once strikes the eye is the hopeless condition of the plants numbered 3, which, having had a meager supply of water, applied wholly at surface, had been left behind in the race at an early day and were now drying up. The plants numbered 4 had received exactly the same amount of water, but it was placed, by the simple method of subirrigation already described, where it would be utilized with a minimum loss by evaporation.
A comparison of numbers 1 and 2 indicates that there is no virtue in subirrigation, in itself considered. It is merely a means of preventing waste. Both of these had received a large quantity of water, the former at the surface, and the latter by way of subirrigation. As far as this experiment goes, then, it appears that aside from alkaline or other conditions requiring special treatment, which it is not the purpose of this article to discuss, water may be applied indifferently at or below the surface, if there is only enough of it. It is simply a matter of supplying the roots of the plant with all the water it requires. But if it only needs about half as much when applied in the simple way that has been described, the fact is of sufficient importance to engage the attention of horticulturists from Colorado to California. It is true that reports on the results of subirrigation, thus far, have not been encouraging in all respects, and the application of such methods on a large scale would necessarily involve a rather large initial outlay; but when one considers the great expense involved in preparing for the irrigation of an orange grove, say, in southern California, and the continual outlay of time, labor and money required by the present wasteful methods of applying water, it may well be asked whether some simple method of subirrigation may not be developed which, when once the practical difficulties have been overcome, will prove in the end more economical as regards cash outlay, and at the same time make it possible for the available water to do double duty.
It is to be borne in mind that with very few apparent exceptions, such, for example, as the areas bordering upon the lower Colorado, the arid states and territories are nowhere possessed of an unlimited watersupply; in most cases there is a fixed limit, beyond which no amount of 'development' will produce more water. If, then, by economical methods, a given quantity of water—all that can be depended upon for a certain area—can be made to irrigate satisfactorily twice as many acres as by wasteful methods, he who shows how this can best be done, and inaugurates the doing of it, will deserve well of his country.
- California Expt. Sta. Bul. 121. 1898.
- U. S. Dept. Agr. Office of Expt. Stations, Bul. 86. 1900.
- Swingle, W. T., 'The Date Palm and its Utilization in the Southwestern States,' U. S. Dept. Agr. Bureau of Plant Industry, Bul. 53. 1904.
- Fairchild, D. G., 'Persian Gulf Dates and their Introduction into the United States,' U. S. Dept. Agr. Bureau of Plant Industry, Bul. 54. 1903.