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After this it was necessary only to supply the water transpired by vegetation and lost by evaporation, the loss being very small on account of the fact that no crust was formed on the surface, and the flocculent, open structure of the soil was little interfered with by this method of applying water. It remains to be seen whether the plan of cementing the joints of the hard-burned tile, except an inch on the under side, will prevent the entrance of roots to the extent of stopping the circulation of water through the pipes. This method has been used also by Dr. Hudson, of Osborne, who has expressed satisfaction with the results. Other than tile pipes have been used for this purpose. Small pipes made of galvanized iron and perforated with very small holes, or preferably with an open seam, have been used and satisfactory results reported. The following description has been condensed from a statement given by Mr. Alex. Richter, of Hollyrood, Kansas, who has used the open-seam pipes.

The first precaution is to ascertain whether the structure of the soil and subsoil is such that subirrigation is practicable, as it is a useless expenditure of money to lay pipes where the conditions are such that the water will not spread laterally to the plants. In some localities the subsoil is so porous that the water applied beneath the surface sinks immediately and can not be had by the roots of any of the plants except those in the immediate vicinity of the source of supply. This is especially the case on the bottom lands along streams where the surface soil rests upon gravel or beds of sand. Where, on the contrary, the subsoil is comparatively impervious, and above this the structure is such that the water is transmitted horizontally, systems of subirrigation can be introduced to great advantage. For example, the following experiment was tried: During a dry season a pipe 10 feet long was laid 10 inches deep in the middle of four rows of string beans, these being about 5 feet apart. Into the pipe 12 quarts of water were poured, and the same amount was sprinkled on four other rows of string beans in all respects similar to the first. In the case of the rows watered by the pipe the beans did well, while in the other rows they died. The same amount of water was given to each.

In 1895 many experiments were made by different farmers, some putting pipes in rows 5 feet apart, others 8 or 16 feet, and in one case 27 feet. Different depths also were tried, some being 14 inches, others 18, and still others 2 feet. During the first five months nearly all of these were satisfactory, but after that period difficulty was found by the persons who had laid the pipes from 18 to 24 inches beneath the surface. By digging down it was found that the deeper pipes had been placed so low as to be embedded in the clay subsoil, and that this did not allow the water to spread freely. By raising the pipes about 6 inches, well above the top of the clay, the water percolated freely. For vegetables it was found that pipes give the best success when laid from 8 to 10 feet apart, while for orchards a single row of

pipes was sufficient between alternate rows of trees, these pipes being placed from 10 to 12 inches in depth. It was also found that the moisture was rendered more efficient by using fertilizers.

One of the most common mistakes at first made has been in giving too great a slope or inclination to the pipes. If laid on ground which has a decided fall the water runs to the lower end before it can escape in considerable part through the opening along the side. For this reason the pipes should be laid very nearly level, but if a considerable slope can not be avoided it has been found best to have cut-offs in the pipe every 10 or 20 feet to check the flow. Another way is to run the main pipe on the down grade and connect this with irrigating pipes branching from it with suitable valves or cut-offs, so that the water can be turned into the branches. The preferred length of irrigating pipe is about 200 feet. Sometimes this can be connected at both ends with the main supply pipes to advantage. The main supply pipe is proportioned according to the amount of water to be carried. In general for gardens and orchards it is 14 inches in diameter. The sheet

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iron irrigating pipe leading from this has an
open seam along its length and is usually seven-
eighths of an inch in diameter, although smaller
sizes can be used for flower beds. The cost
varies according to the amount used, but in one
case where 3 acres were provided, 2 of these
being orchard and the remaining acre devoted
to potatoes, watermelons, and other vegetables,
the entire cost was $63. In this case the water-
melons alone paid the cost of the pipe.
man can lay nearly 3,000 feet in a day, covering
it up by means of a plow.

One

There is a notable difference in the distribution of moisture when the subirrigating pipes are laid above the surface of the clay and when they are put down in it. In the first case, when the pipe is buried in the pervious soil slightly above the impervious clayey subsoil, the water spreads laterally upon the surface of the latter, moistening the ground upward while spreading out beneath the surface. In the second case, when the pipe is within the clay, the water can not spread laterally, but rises slowly and moistens only a narrow belt immediately above the pipe, not finding its way as rapidly as in the other case along the surface of the clay.

This difference in behavior is illustrated by an experiment in which two pipes were laid above the subsoil and five pipes below the clay. The two pipes were able to deliver far more water than the five more deeply buried. An examination by a test pit showed that although the surface was dry above the five pipes, there was standing water in the clay. This fairly uniform distribution of water from the pipes when laid above the subsoil is said to obviate the difficulty found with the roots of trees. The great objection to this form of subirriga

tion has been that after one or two years the fine roots of plants seeking out the water inclose the conducting pipe and penetrate every opening or crack, finally completely obstructing the flow of water. Where, however, the moisture is distributed uniformly through the soi!, the roots are not impelled directly toward the pipe. Cases have been reported where pipe has been used for three years successfully at a distance of only about a yard from a row of trees.

AMOUNT OF WATER REQUIRED.

There are two ways in which quantities of water used in irrigation are expressed. One is in terms of the rate of flow, as, for example, that of a river; the other is in quantities of water, such as would be held by a reservoir. In the first case we speak of a stream as averaging through the month of August 10 second-feet or 500 miner's inches. In the second case we speak of a reservoir as holding, in round numbers, 6.46 million gallons, or 862,000 cubic feet, or 19.8 acre-feet. Each of these can be converted into the other by simple computations. Where water is spoken of according to the rate of flow, the total volume can be obtained only by assuming a certain length of time during which the flow continues. On the other hand, the volume of water, as, for example, that stored in a reservoir, can be converted into rate of flow by figures based upon the number of days or seconds during which the quantity is to be discharged.

In discussing rates of flow of a natural stream, the cubic foot per second or second-foot has been generally adopted as the standard, and is rapidly displacing the older, indefinite term-miner's inch.

The cubic foot per second, or second-foot, is the rate of delivery of a stream 1 foot wide and 1 foot deep, flowing at the average rate of 1 foot per second. The quantity is, of course, independent of the shape or velocity of the water; a second-foot will be delivered by a pipe 6 inches in diameter in which the average flow is a trifle over 5 feet per second, or by a ditch having a cross section of 4 square feet and a sluggish current of only 3 inches per second.

The miner's inch is a unit adopted for convenience by the hydraulic miners of the West, and, being easily arrived at through rough devices, has been largely employed throughout the arid region in estimating the quantities of flowing water. The chief objection to it is its indefinite character. One miner's inch may be 20 or 25 per cent larger than another, although both are measured according to established rule or customs. In early days, when water was abundant and it had little value, there was no especial demand for accuracy in its measurement, and the crude devices sufficed for all practical purposes; but when the streams came to be used for agriculture and it was appreciated that values resided in the flowing water rather than in the land, it made considerable difference to a farmer whether his miner's inch of water was large or small. To avoid confusion and litigation, the term "miner's inch" has therefore been largely done away with IRR 5-3

and quantities are given in fractions of a second-foot. In California the miner's inch is now given as one-fiftieth of a second-foot, while in Colorado and many other of the Rocky Mountain States it is nearer the fortieth part of a second-foot. In other words, the Colorado

miner's inch is considerably the larger.

The second method of stating the quantity of water-that by actual volumes rather than by rate of flow-is in all respects the more accurate and desirable, and is the only practicable means in localities such as those on the Great Plains, where water must be pumped or stored and is not running continuously to waste when not used, as is the case along the larger streams of the arid region. The units employed may be the gallon, the cubic foot, or the acre-foot. The United States gallon, as defined by statute, contains 231 inches; 7.48 gallons make a cubic foot, or 1 gallon is 0.13368 of a cubic foot. The chief disadvantage of the gallon as a unit is that it is too small and requires large figures to express the amount needed for irrigation. It has also the additional disadvantage that there are other gallons of other sizes in use, so that confusion occasionally arises.

The cubic foot is a definite quantity and is very convenient for use in computations of the amount of water required. By its use the capacity of reservoirs can be readily computed, since their dimensions are usually expressed in feet. It is, however, like the gallon, too small for convenience in many estimates, and in practice it has been largely replaced by the acre-foot. This latter term implies a quantity equivalent to the amount of water covering 1 acre to the depth of 1 foot. In other words, 1 acre-foot equals 43,560 cubic feet. This quantity-an acre-foot-does not imply that the water must be spread out 1 foot in depth, for the 43,560 cubic feet can be placed in a reservoir of any shape and still be an acre-foot. It may be held, for example, in a pond 100 feet square and to a depth of a little over 4.3 feet, or it may be in a tank 20 by 50 feet and 43.56 feet deep. There is a convenient relation between the acre-foot and the cubic foot per second, or second-foot. The latter flowing for one day (twenty-four hours) very nearly equals 2 acre-feet; that is to say, a stream 1 foot wide and 1 foot deep, flowing at an average velocity of 1 foot per second, will in one day, or 86,400 seconds, cover a surface of 1 acre to a depth of very nearly 2 feet.

The term "duty of water" has been employed to express the relation which exists between the quantity of water used and the area of land irrigated. For example, if a stream of water equivalent to 1 cubic foot per second irrigates 100 acres, the water duty at that place is stated as being 100 acres to the second-foot. This water duty may be arrived at from two opposite directions. First, as given above, by taking actual instances of the measured amount of water applied; and second, by starting at the other end and estimating the theoretical amount which the plants require and the quantity which must be wasted in wetting the ground before the water can be available for the

need of the plants. Neither of these is wholly satisfactory, and there has not as yet been obtained a sufficiently large body of facts to enable conclusions of general applicability to be drawn. Taking any one crop through successive years, the amount of water actually used varies so widely that it is doubtful whether any figures yet published can be implicitly relied upon.

A large number of experiments have been carried on, not only in Europe but in this country, to show the amount of water exhaled by plants. The results of these, as above stated, are discordant, but as a rough statement it may be said that the plants have transpired during their growth a weight of water from 300 to 500 times that of the weight of dry matter. In this country various agricultural stations have obtained and still are obtaining data bearing upon this point. Among the best of the published results are the series of experiments conducted by Prof. F. H. King at the Wisconsin agricultural station. These are of particular value in this connection as showing the amount of water required by plants even in a humid climate. The results of the observations for 1892 show the following amounts of water consumed per pound of dry material produced:

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The data given above have been combined with those obtained for 1891 and computed in other units, giving the corresponding depth of water used in the production of the plants. These results are shown in simplest form in the following table:

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