In the above summary Dr. Wollny touches upon various phases of evaporation which have an important bearing on Western irrigation. At present there is little data to enable us to compare intelligently the results obtained in Germany with those in this country. However, some of the Agricultural Experiment Stations are taking up this work, and in a few years we may hope to know much more of the behavior of soil moisture and ground waters and their relation to plant life. The main object to be attained in the artificial application of water to soil is to develop plant life, and as this can be accomplished only by creating a moist soil and subsoil, it is necessary that we endeavor to ascertain the greatest possible percentage of the total precipitation that can be used for this purpose. In this State evaporation from both water and land surfaces must be regarded as one of the chief sources of waste, and as such deserving of careful study.

TRANSPIRATION.

In arid America agricultural products are almost entirely dependent upon the water supply. As a rule, the soil is fertile, containing in abundance the elements necessary for the development of plants; but if the water supply be either deficient or applied at the wrong time, a partial growth will result. The portions of a wheat field that are missed at the first irrigation seldom yield one-third of a crop. These dry places may be irrigated subsequently, but the second watering can not restore the shrunken cellular tissues nor the lost vigor. The skilled horticulturist has learned by experience and observation how and when to irrigate his fruit trees. When the trees are young, water is conveyed in two furrows only, one on each side the row of trees and at some little distance beyond the farthest roots. As the tree grows, the roots thrust themselves farther into the soil, but chiefly in the direction of the water supply, and in the following season the two furrows may be increased to four, until finally, in well-matured trees, all the space of 20 feet or more between the rows is thoroughly watered. By such a method water is not only provided for the soil, but is applied in such a way as to lead out the roots in quest of moisture and food.

Much has been written recently on subirrigation, and many agricultural experiment stations have gone so far as to pronounce this method superior to all others. By it water is conveyed through pipes buried in the ground and is discharged through a large number of small holes located opposite each tree. This mode of irrigation has not been successful. In the first place, it is an impossibility to cause water to discharge equally through so many orifices; and in the second place, the water is deposited at particular points in the soil, around which the roots of plants are sooner or later massed. The few advantages to be gained by applying the water beneath the sur

face can not be compared to the disadvantages due to the difficulties in the way of its distribution and to the concentration of the roots at particular places.

The injurious effects upon vegetation caused by either too little water or too much are clearly illustrated by the results of experiments made by Dr. E. Wollny1 on summer rape, as given in the following table. In this, the first column gives the per cent of water in the soil as compared to the total water-holding capacity. The second column gives the number of pods produced, and the following columns give the weight of the various parts:

Effect of excess and deficiency of moisture.

In growing plants in pots it is possible to apply just the right amount of moisture, but on the irrigated field it is somewhat different. At each watering the ground is for a time nearly saturated. Part of this excess water is soon evaporated, either from the ground or indirectly through the foliage. Another part sinks into the subsoil, and the remainder keeps the soil moist. If this soil moisture can be maintained in the right proportion, or, in other words, if the amount drawn from the subsoil by capillarity equals the loss by evaporation until the next watering, the crop will grow under the most favorable conditions as regards moisture. If too little water is applied to the surface and the subsoil water for some cause is inaccessible, the crop will suffer and become more or less dwarfed. On the other hand, too much water may keep the soil near the extreme of complete saturation and produce upon vegetation as harmful effects as too dry a soil. A cubic foot of average soil when thoroughly saturated will contain from 25 to 30 pounds of water. According to Wollny's experiment, the best results were obtained on summer rape when about 40 per cent of the empty space in the soil was filled, which would be equivalent to from 10 to 12 pounds of water in every cubic foot of soil.

We may thus classify productive soils under three heads in relation

1 Experiment Station Record, Vol. IV, p. 532.

to the percentage of moisture which each contains, viz, as dry soils, moist soils, and wet soils. It may also be said that in each of these classes the amount of water drawn up by the roots and transpired by the leaves differs. The magnitude of this transpiration of vapor through the foliage of plants has been investigated by Messrs. King, Wollny, Hellriegel, and others, the results of whose labors are briefly summarized in the following tables:

Amount of water required for a pound of dry matter in Wisconsin.1

Ratio of water evaporated to weight of crop harvested, as shown by experiments

According to Hellriegel, as shown by the above table, 330 tons of water would be absorbed by the roots of clover, drawn up through the stems, and evaporated from the breathing pores of the leaves, for each ton of clover harvested. If the yield be estimated at 3 tons per acre, the quantity of water per acre is 990 tons, or a volume sufficient to cover the surface to a depth of nearly 9 inches. So far as has been ascertained, no tests have been made in the Rocky Mountain region

F. H. King, Agricultural Experiment Station, University of Wisconsin, Ninth Annual Report, 1892, p. 94.

2 Department of Agriculture, Experiment Station Record, Vol. IV, p. 532.

of the amount of water actually consumed by the various agricultural crops between the time of germination and the harvest, but observed facts seem to indicate that this amount varies with the conditions of soil moisture.

In sections of northern Utah, where water can not be readily or cheaply conveyed to irrigate the land, the fields are usually sown in wheat and cultivated "dry," the annual yield being from 12 to 25 bushels per acre. During the period of growth the rainfall is occasionally less than 1 inch, and the soil and subsoil apparently are very dry. If the quantity of water consumed by the wheat was even onethird of that given by Prof. F. H. King for barley and oats, which averaged a depth of nearly 19 inches over the entire surface cultivated, it is difficult to conjecture where the supply could come from. On irrigated lands the case is quite different. The proper amount of moisture is maintained in the soil, the plant is kept in a healthy, vigorous condition, and the normal amount of water passes through its tissues, bearing the necessary mineral food furnished by the soil. It is not unusual to irrigate alfalfa every other week, and to spread an amount of water over the surface during its period of growth sufficient to cover the ground to a depth of 6 feet. A part of the water used in irrigating usually sinks into the subsoil and flows off as seepage water, a second part is evaporated, and the third part, possibly one-third of the whole supply, passes through the tissues of the plant and is mostly transformed into vapor at the leaves.

The sagebrush and grasses indigenous to the uncultivated lands of the Rocky Mountain region require but little moisture to maintain their slow growth. In the vicinity of Corinne, Boxelder County, Utah, the average annual rainfall for the past twenty-five years has been less than 12 (11.73) inches. Little snow remains for any length of time on the ground; the evaporation in summer is excessive on all moist ground and water surfaces; and yet sagebrush flourishes, growing to a height of from 3 to 5 feet. If we deduct from the total yearly precipitation the probable amount of moisture evaporated, very little will remain for the use of the plants. It is possible that the total quantity of water absorbed by the roots of the plants that grow on uncultivated lands and transpired by their foliage does not exceed one-tenth of the annual precipitation, which in this State would be about 1 inches over the surface of unreclaimed arable lands. On the preceding estimates, based on observed facts, we may therefore conclude that in this State the amount of water evaporated from the foliage of plants ranges from a surface depth of 1 inch for buffalo grass and sagebrush to a surface depth of 20 inches for well-irrigated alfalfa.

CACHE VALLEY.

This beautiful valley is nearly surrounded by mountains. A spur of the Wasatch Range forms the elevated divide between it and Bear Lake Valley, in Rich County, to the east, and another spur of the