From the above table it is to be observed that the least amount of water used was by the barley in 1891, and it should be noted that the product for this year was only about half that for 1892, while nearly double the amount of water was used. It is probable, therefore, that if the barley had received or used as much water as the same crop in 1892, the production of dry matter would have been greatly increased. It has been found that there is a great range in the amount of water employed by various plants in the process of building their tissues, and that not only do the different species stand widely apart in this respect, but even individuals of any one species at the successive stages of life or with alternations of climatic conditions transpire water more or less freely. As previously noted, the experiments, when reduced to a common basis, show a wide range in results, depending largely not only upon the conditions under which the tests were carried on but also upon the assumptions necessarily made in reduction to the same form of statement. Thus the water used by a crop of wheat is from 9.3 to 29.8 inches in depth, averaging 17.9 inches; by barley, from 4 to 30 inches; the same experiments in successive years obtaining 13 and 23.5 inches, the difference, however, being in part accounted for by the increase in yield.

In actual crop production, however, it is necessary not only to satisfy the thirst of the plant but also to fill certain demands of the soil necessitated by its composition, structure, and exposure to the air. A certain amount of water must be given to the soil before the plant can obtain any for itself, and, according to the skill of cultivation, more or less of this water will be taken up directly by the air or by weeds. The process of getting the water to the crop, usually in openearth channels, is also more or less wasteful, so that beyond the plant's needs there is always to be added a variable percentage to cover these various losses. Many of these losses may be reduced or prevented by more perfect systems of irrigation and cultivation, but there is always a limit to expenditures in this direction set by the market value of the product. In other words, it will not pay to push water economy in this direction beyond moderate efforts.

To obtain valid conclusions as to the total amount of water required by the plant, together with that portion lost in transit in the irrigating channels and in the soil while waiting for the demands of vegetation, it is necessary to resort to the results of field tests made in various localities under local conditions of soil and climate. There are, unfortunately, comparatively few data as yet sufficiently complete for generalization, and these, as might be expected from an analysis of the matter relating to plant transpiration, offer wide discrepancies.

Experimental data are still lacking as to the exact amount of water required for the proper moistening of plains soils to any depth. It is not unusual with alfalfa to apply 6 inches of water, or over 680 tons

per acre, at a single irrigation, but with the usual field crops it is probable that 3 acre-inches at an application is more usual than a larger quantity. Experience of irrigators generally favors the application of enough water to moisten the soil to a considerable depth, say 14 to 24 feet, and then by cultivation producing a mulch of fine soil on the surface to retard evaporation, thus retaining the water of a single irrigation for the use of the deeper roots of the plants for a considerable period, rather than the more frequent application of small quantities, which, by moistening only that portion of the soil very near to the surface, encourages the growth of roots in that portion of the soil which soon becomes dry. Such irrigation leads to spasmodic and irregular growth and often to serious injury to the plant from drought, even though very frequently watered. For general purposes it is undoubtedly the best plan to have the subsoil well moistened early in the season and to keep up the supply of moisture by such copious subsequent irrigation as will encourage the development of deep roots and maintain the uniform maximum growth of the plants.

A convenient figure in estimating the quantity of water to be applied to orchard and ordinary crops at a single irrigation is 100,000 gallons per acre. This will allow of some loss by seepage in the ditches, and usually moistens the soil to a good depth if judiciously applied, and can by the furrow system generally be so applied as to leave the soil in good condition for growth.

The quantity of land which may be irrigated by a single man in a given time is exceedingly variable, and depends greatly upon the skill with which the land has been graded and the ditches have been laid out and constructed. Twenty acres per day may be as easily irrigated under some conditions as 1 or 2 acres under other conditions. In garden operations, of course, the areas covered are usually much less than in the big fields, and a man may sometimes spend a whole day on very much less than an acre and have no reason to chide himself for inefficiency.

WINTER IRRIGATION.

On the plains the winter and early spring months are usually dry, and the soil is sometimes almost as devoid of moisture at the opening of spring as during subsequent droughts. This powdery soil is easily worked, and some have thought it in favorable condition for the reception of seed, and that copious watering later would be sufficient to insure the full benefit of irrigation. But disappointments have sometimes resulted, scarcely better crops being realized than where no water was applied artificially. On the other hand, where similar soil has been thoroughly moistened by the late winter or early spring rains, or by winter irrigation, the fertility of the soil has been amply demonstrated. Whatever may be the explanation of the fact, it has been

found by nearly all observant irrigators of the plains that winter irrigation, thoroughly done, serves very well the double process of fertilizing and moistening. Mr. Perry states that after his eight years of extensive experience in irrigation, he has had the best average results where he has thoroughly saturated the soil to a depth of 2 or 3 feet during the fall or winter or very early spring, and then has cultivated his crops on this land without subsequent irrigation. Mr. C. B. Huffman, of Enterprise, Kansas, has found that land thoroughly irrigated and well cultivated during the season of 1895, and afterwards sown in wheat, produced suprisingly well in 1896 without any irrigation after the wheat was sown, while similar land that had not been irrigated gave a very poor yield. The general experience of orchardists favors winter irrigation. Not unlikely, future practice in the application of water will consist in thoroughly wetting the soil during the winter and in such subsequent irrigation as may be found desirable to maintain the maximum growth, the larger quantity of water being applied in the winter, when evaporation is at a minimum.