|Standard Cyclopedia of Horticulture|
Irrigation. Irrigation in its broadest sense includes all problems of collecting, storing, delivering, and applying water to the land through the construction of dams, reservoirs, canals and laterals, and the application of power when necessary to deliver the water; while in a restricted horticultural sense it is a method of cultivation, having for its object to increase and regulate the water-supply in the soil.
In this latter sense, irrigation is a necessary practice in the arid regions, and is advisable in the humid regions in proportion to the intensity of the cultivation and the value of the crop grown. Thus in Florida, with an average of 60 to 70 inches of annual rainfall—usually well distributed—irrigation has been largely introduced in the past few years for horticultural crops and even for tobacco, as an insurance against loss or damage by the occasional drought. The first cost of a small irrigation plant in Florida, for 20 acres or over, is said to be approximately $100 to $150 an acre; the interest on which, and the necessary repairs, would amount to $5 to $10 an acre each year. This is a small expenditure, to insure a crop against loss or injury where the value to the acre is so great as in many horticultural lines. Irrigation is needed not only to prevent the actual death of the plants, but to promote a uniform, rapid, and continuous growth, which is necessary for the development of the finest texture or flavor of the commercial crop.
King has shown that the value of a crop saved in Wisconsin, such as the strawberry, in a season when the crops generally are injured by drought, may pay all the expenses of the original cost of the irrigation plant.
In the semi-arid regions west of the 100th meridian, with a rainfall of 20 inches or less, crops are liable to be entire failures three or four years out of five; while with an irrigation plant there should not be a failure one year in five. In the arid regions with less than 15 inches of rain, irrigation is a necessity on most soils. Here the work has been highly organized and systematized, so that the cost of water delivered at the field amounts to $2 to $5 an acre each year. Under skilful management, the most abundant yields are secured. The most careful management is required in the application of water to prevent serious injury to the land and to avoid actual injury to the crop in rendering the plants tender and liable to disease, and in maintaining the quality and flavor, both of which are liable to depreciate unless good judgment is displayed in supplying water.
Sources of water-supply.
The principal sources of water-supply are streams, surface wells, artesian wells, and the storage of storm waters. For small irrigated tracts near cities, the city water-supply may often be used to advantage. In other localities the nature of the conditions will determine the most economical source from which to secure the water. Perpetually flowing streams, if situated in such a way that water can be carried to the land by gravity, have the advantage of cheapness of construction and maintenance. On the other hand, if the stream supplies others in the community, there is liable to be trouble and expense in establishing and maintaining water-right claims and in securing water when needed for the crop. Questions arising out of the water-rights on streams and rivers in the western states, with the various state laws, the multiplicity of court decisions on the most intricate legal questions— both in different states and different countries along the line of the stream—the absence in most states of adequate police or judicial powers vested in the irrigation commissioner, have led to the most perplexing and bewildering state of affairs, and have involved the states and individuals in enormous costs for lawsuits, resulting in many cases in the apportionment of many times the volume of the stream to the settlers along its bank.
The large planter must seek some perennial and abundant supply of water, as is furnished by streams, but it is safe to say that all streams of any size in the western part of the United States are already appropriated to their fullest extent, although the water so appropriated is not all in present use. Smaller planters are much more independent with some of the other sources of supply mentioned above. Wells from 10 to 20 feet deep, with pumps operated by windmills, or wells of a maximum depth of 50 feet operated by many forms of gasolene, hot-air or portable engines, attached to direct- acting pumps or centrifugal pumps, form in general a very satisfactory means of irrigating small areas.
Over limited areas artesian wells have been very successfully used. If they are flowing wells delivering a considerable stream, they can be used over small areas without storage reservoirs, or over much larger areas with reservoirs. They should be capped in all cases, where possible, so that the flow can be stopped when not actually needed.
In many places it is possible, at a comparatively small expense, to construct a dam to collect the storm waters. The magnitude and expense of such work will depend entirely on the configuration of the surface, the area of the watershed, the volume of the water to be handled as well as the nature of the soil, and the material out of which the dam is to be constructed.
Methods of raising water.
Various methods are used for raising water from streams, wells, or storage reservoirs which may lie below the general level of the land to be irrigated. Hydraulic rams are sometimes used for small areas, but these are not economical when a small volume of water is at hand, as only about one-seventh of the water can be collected. Open buckets carried on an endless belt, operated by either windmills, or steam-power or even horse-power, are used with success and offer the advantage of cheap construction. The ordinary cylinder or plunger pumps are usually employed when the water has little or no sediment, and are operated by windmills or by steam or other form of engine. When the water carries considerable sediment such pumps are liable to wear away rapidly, and the centrifugal pump is the most economical form to use. The relative first cost of equipment for pumping with windmills or with gasolene or hot-air engines of approximately equal horse-power is about the same. The windmill, however, is dependent upon a mean velocity of wind of about 8 miles an hour, while the engine may be operated at any time, and is thus more reliable when either form of motive power is taxed to nearly the extreme limit. There are many kinds of windmills on the market, and many forms of home-made construction are in use.
Storing and conducting water.
Storage reservoirs for streams and for storm waters vary in size and in cost mode of construction according to the character of the land, size of area, volume of water, nature of the material of construction, and demand for the water. The construction of such reservoirs sometimes involves engineering problems of the most difficult kind, demanding the expenditure of immense sums of money.
In the use of windmills, it is necessary to have small distributing ponds or tanks, as the direct flow from the pump is usually so small and varies so much with the velocity of the wind that it cannot be depended on to water any considerable area. Where it is stored it can be turned out on the land in large volumes, so that it spreads over the surface and waters the whole area uniformly. For an ordinary windmill the ponds are from 50 to 100 feet square. They can be stocked with fish and thus be a source of some revenue and variety in the family supplies. Unless the pond is situated on a slight elevation, the earth for the embankment must be taken from the outside. The banks are usually made with a slope of 1 1/2 to 1 foot. For a bank 5 feet high and 2 feet across the top, the side would be about 7 ½ feet and the base about 13 feet wide. If the ground is at all pervious to water, the bottom of the pond should be protected from undue seepage and loss of water by puddling. This should be done with clay, if this is obtainable. This puddling is often done by driving horses or cattle in the pond while the surface is wet. A pond of the size indicated above, operated by a windmill where the mean wind velocity is about 8 miles an hour, will irrigate from 3 to 5 acres of land in the semi-arid regions. Such a pond could be counted upon to irrigate from 5 to 10 acres where, as in the East, only one or two irrigations would be required during the season. The size of the reservoirs and the area they will irrigate, when supplied by steam or other kind of engine, will depend upon the available water-supply and upon the size of pump and power used.
Ditches and flumes.
The water is usually carried from the stream or storage reservoir by gravity in open ditches. This involves loss by evaporation from the surface and by seepage through the soil. When the water-supply is limited and its value is consequently great, terra-cotta pipes, iron pipes, cement or wooden pipes may be used. When the surface of the country is uneven and ravines have to be crossed, flumes are used to carry the water on an even grade across the depression. These flumes may be iron pipes, open wooden troughs, or wooden pipes held together with substantial hoops. If the depression is not too great the ditch may be built up on an earth embankment. When the water has to pass through a gravelly soil, or when for other reasons the soil is very pervious, special precautions should be taken to prevent seepage by using pipes, cementing the sides of the open ditch, or puddling the ditch with clay or similar material.
Application of water.
The water is usually applied to the ground by flooding over the whole surface. For this purpose the surface must be perfectly level and the ground carefully prepared, so that the water will flow uniformly and quickly over the entire area and be of uniform depth throughout. When crops are cultivated in rows or on beds, the water is allowed to flow down in the troughs between the rows, and there must be a sufficient head of water to reach the ends of the rows in a reasonably short time, so that the whole width of the field will be properly watered.
Where the surface of the ground is so uneven that surface flooding cannot be used, basins arc formed by throwing up slight ridges, with a plow or other implement, and the water turned into these basins in succession and allowed to accumulate to a sufficient extent. This method is particularly applicable to fruit trees, although it is occasionally used in other crops. In very sandy soils the water is occasionally carried through the field in wooden troughs, which admit of sufficient seepage to water the land. This prevents the undue seepage which might occur in such soils if the water was flowed over the surface. Another method is to distribute the water through the field in iron pipes, with openings at frequent intervals, in which nozzles can be attached to deliver a fine spray over a small area. With four or five such nozzles an attendant can water a considerable area of ground in the course of a day. Such an irrigating outfit in Florida was supplied with a power equivalent to about one horse-power an acre. The mains and laterals were of 1-inch or 1 1/2 -inch iron pipes laid near the surface of the ground, the laterals about 100 feet apart, with hydrants every 50 feet. Tanks were originally used, but it was found desirable to pump directly into the mains to insure a sufficient pressure.
Care should be exercised in applying water to the land. Where water is plentiful there is a common practice of using such an excess as to injure the flavor of fruit, increase the liability of disease, and eventually injure the land by the accumulation of seepage waters and of alkali. As a rule, there has been very much more damage from over-irrigation than from the use of too little water. The first two or three years a soil usually requires a considerable amount of water, but after becoming well moistened to a considerable depth it should require comparatively little water thereafter to maintain its fertility. As it is not easy to apply just the proper amount, the excess should be provided for. If there is any reason to fear lack of drainage, the land should be thoroughly underdrained before irrigation is started, or at any subsequent time when the need of it becomes apparent.
Irrigation always should be supplemented by the most thorough cultivation. After going to the expense of watering the soil in this way, it is poor economy to allow the water to escape by evaporation or otherwise; therefore every precaution should be used in thorough, subsequent cultivation and in the exclusion of weeds, to conserve the moisture so applied. The intelligent horticulturist will find that in the use of this expensive method of maintaining a proper water-supply in the soil, it is incumbent upon him, even more than if the method were not used, to give careful attention to all the ordinary methods of preparation and cultivation in order to maintain the advantages he has established by the irrigation plant.
Sub-irrigation in the greenhouse.
The term sub-irrigation is used to describe a method of supplying water to the roots of plants by means of some form of conduit placed below the surface of the soil. In greenhouse operations, the essential features of the plan are a level water-tight bench-bottom, and tile, or pipes, to serve as conduits for the water. The tile, or pipes, are laid directly on the bench-bottom, and over these the soil is spread, usually to the depth of about 6 inches. When water is introduced in sufficient quantities through the tile or pipes, it passes out at the joints, or perforations into the soil.
When applied to greenhouse operations, the term sub-watering has been proposed by E. S. Goff, for the reason that irrigation is used to denote watering on a large scale out-of-doors. It may be said, however, that the words watering and irrigation do not indicate the scale of operations with any degree of accuracy; therefore it seems as well to use an old word as to coin one, especially when the familiar word expresses the meaning intended.
Experiments in watering plants by this method were begun in the winter of 1890 and 1891, at the Ohio Experiment Station. The suggestion came from the result obtained in an effort to check the lettuce rot. Water was introduced to the soil in boxes by means of a pipe, in a manner similar to the method often employed in watering hills of melons and cucumbers. When the plants were watered in this manner, the lettuce showed so much more vigor than that watered in the ordinary way, that operations were begun at once on a larger scale; first in a bed on the ground having a clay bottom, then on a water-tight bench, made of lumber, and finally, on tile benches, covered with cement.
In all of the earlier experiments the water was introduced through pipes, or drain-tile, laid about 2 feet apart on the bottom of the benches. Goff has used brick instead of tile, placing them near enough together to touch. They were set on edge in a galvanized iron pan, made for the purpose. J. C. Arthur clipped off the corners of the bricks, so as to facilitate the flow of water. The Ohio Station has modified this plan by using common drain-tile, laid so as to touch, thus covering the entire bench bottom, instead of lines of tile every 2 feet, as at first.
Benches made of lumber have proved unsatisfactory because of the swelling and warping of the boards. Solid beds on the ground have not been successful, except where an impervious clay bottom existed. Galvanized iron adds greatly to the cost of construction, and lasts only a short time. The only suitable bench for greenhouse sub-irrigation is one made of materials which are not acted upon by water.
A well-made tile-and-cement bench seems to be the only form of construction that will meet the requirements. Such a bench does not cost so much as to preclude its use, and will last as long as any other part of the greenhouse. In describing such a bench, it will not be necessary to enter into details, except such as relate to the method of watering under discussion. The bench must be water-tight, and this essential condition is secured by spreading a layer of cement, an inch or more in thickness, over the tile bottom. It is not a matter of any moment whether flat tile or common drain-tile are used, except in the quantity of cement required. The cement must be spread with care, so as to secure a perfectly flat level bottom, otherwise the water will not flow uniformly in all directions. The sides of the benches are made of cement also, but need be only 2 or 3 inches high, or of sufficient height merely to retain the water. Boards or slate are placed outside the cement wall to retain the soil. The tile-bottom may rest on iron or wood cross-pieces. Wood has been in use for this purpose at, the Ohio Station for twenty years and shows no signs of decay, because it is out of reach of the water.
Twenty years' experience shows that a perfectly constructed bench-bottom, with the tile laid 2 feet apart, will serve satisfactorily in distributing the water to all parts of the bed, provided the tile are straight, so as not to impede the flow of water. The tile are laid in the same manner as tile-drains, and lengthwise or crosswise the bed, as preferred. Better results are usually secured if they are laid crosswise than lengthwise, as it is difficult to secure an even flow from long lines of tile. A little cement or mortar is used at each joint simply to hold the tile in place when the soil is put in the bench, but not enough to impede the flow of water from the joints. The first tile where the water is introduced is laid at an angle, one end resting on the edge of the bench side. This leaves a wide opening at the first joint, which is closed with cement. A better plan is to use a curved sewer-pipe for the inlet, but this is not always available. The picture (Fig. 1979) shows how the tile is laid on the bench bottom, being a view of a side bench in a carnation-house.
Following Goff's suggestion in the use of brick, tiles have been used over the entire bench-bottom with good results, and it seems probable that this will be found to be the best form of construction, as it appears more certainly to insure an even distribution of water. The method of construction is the same as above described, for the two plans differ only in the number of tiles employed to distribute the water. When the bench-bottom is covered with tile, placed near enough together so that the soil will not fall between, it will readily be seen that water introduced at any point will flow to all parts of the bed in and around the tile. It needs simply to be brought up to such a level that it will reach the soil, when capillary attraction will complete the distribution. Fig. 1980 shows a bench in a tomato house constructed after this plan. AA are the inlets; B the irrigating tile, from which the soil has been removed; C is the tile bench-bottom, covered with cement. The same size of tile, viz.,2 ½ - or 3-inch, is used both above and below. D is the cement side, which has been broken away to show the method of construction. The outer board has been removed also.
The cost of construction need not be discussed here, except to state that the only items extra, more than are required in any well-constructed greenhouse, are the cement bottom and the tile in which the water is distributed.
A plan has been devised for applying water to small plants in flats which may properly be mentioned under this head. The flats are shallow boxes with slatted bottoms. When the plants require water, the flats are placed in a shallow vat of water and allowed to remain until the surface of the soil appears to be damp, or even wet.
A watering in this manner is far more efficient than by the ordinary method. Taken in connection with sub-irrigation in the benches, a crop of lettuce can be brought to marketable size nearly two weeks earlier than when surface-watering is practised. Anything like a full discussion of results of experiments in watering plants in the greenhouse by sub-irrigation would be too voluminous for an article in this connection. A brief review of the results obtained at some of the stations, together with a short discussion of some general principles, will serve the purpose intended. The increase in weight of lettuce from sub-irrigated plats over those watered in the ordinary manner has been reported by Rane, as 25 per cent and by Goff and Cranefield as 26 per cent. At the Ohio Station the range has been from 25 to 100 per cent. In the latter case the result was obtained by commencing with the plants as soon as taken from the seed-bed, and carrying the two lots through to the termination of the experiment, one by watering altogether on the surface of the soil, the other by sub-irrigation. Each of the experimenters speaks of a gain in earliness of several days, by sub-irrigation. Rane secured similar results with long-rooted radishes by this method of watering, but not with the turnip- rooted sorts, while Munson doubled the crop by watering below. Better results have usually been secured at the Ohio Station with the turnip-rooted than with the long varieties, but in all cases there has been a gain in favor of sub-irrigation, varying from 50 to 100 per cent. Rane found that sub-irrigation increased the yield of tomatoes, but the gain was not large. Essentially the same results have been secured in Ohio. The tomato crop has not been greatly influenced by the manner in which the water was applied, and the same is true of beets, while sub-irrigated cucumbers and parsley have shown a decided gain over surface-watered. Carnations, roses, chrysanthemums, sweet peas, violets and smilax have been under experiment by the two methods of watering, and while no such marked results have been secured as with lettuce and radishes, the sub-irrigated plats have shown superiority over those watered in the ordinary manner, in nearly all cases. With carnations the improvement has been mainly in length and stiffness of stem.
Aside from the increase of crop secured by sub-irrigation, there are other considerations which may be urged in its favor, and these are embodied in the following general propositions:
1. Watering by sub-irrigation in the greenhouse saves labor. The amount of labor saved depends mostly upon the completeness of the arrangements for watering, but there is a saving in the number of applications as well. It is possible to reduce the time employed in watering a house, or series of houses, to one-fifth the time usually required.
2. Watering by sub-irrigation assures an abundant and uniform, supply of water to all parts of the bed. Perfect construction of the benches is assumed in this case, but with such construction watering becomes almost automatic, the only care necessary being to look after such portions of the beds as may, by position, be subject to unusual conditions of air or sunlight.
3. Where sub-irrigation is practised in the greenhouse, the surface of the soil does not become compacted, but retains its original loose, friable condition. It is true that where frequent syringing is practised the surface of the soil becomes more or less hardened, but not to the extent that occurs in surface-watering, and the condition is easily remedied, whereas in the other case it is not. It follows that a heavier soil may be used for sub-irrigation than with surface-watering.
Still other considerations might be urged in favor of this method of watering, but many of them would apply to special cases only. Regarding the effect of the method upon insects and diseases, but little can be said. Lettuce rot is less prevalent upon sub-irrigated plats than upon those which are surface-watered, but in extreme cases plants succumb to the disease, whichever method of watering is practised. Munson found that radishes suffered more from the attacks of millipedes upon sub-irrigated plats than upon plats watered in the usual manner. Nematodes work upon the roots of roses, whichever way the plants are watered. The manner of watering has no apparent effect upon the red-spider. Even in houses watered wholly by sub-irrigation this pest is no worse than in houses where the water is applied to the surface of the soil. It may be said, however, that nearly all classes of plants are more easily kept in a healthy growing condition, and are thus better able to resist enemies of all sorts, when sub-irrigated than when supplied with water in the ordinary way.
This method of applying water to plants in greenhouse benches has now been sufficiently tested to determine its value. All that now remains is to devise ways and means to utilize what is known concerning it. The adaptation to suit particular cases must be made by individuals, but this will be far easier in the future than in the past, because better methods of construction prevail than formerly. The success of sub-irrigation in the greenhouse is now simply a question of mechanics. W.J. Green.
In this Cyclopedia, it is not the purpose to discuss the general agricultural practice of irrigation but rather those phases that apply particularly to gardening operations. In arid countries, the garden irrigation practice will naturally follow the general methods of the region. In humid countries or regions, the practices may be very special. In the growing of strawberries and garden vegetables in the eastern United States, special irrigation practices are developing, and these may be briefly considered.
Success in crop-growing depends on many factors. If one of these factors is deficient to such an extent as to limit the crop in yield or quality, no.excess of the other factors will suffice to make up the lack. Thus, if nitrogen is present in the soil in only very minute quantities, no amount of phosphorus or potash will enable the plant to offer the husbandman a worthy harvest. In vegetable-gardening the amounts expended in making the various conditions favorable are relatively large. Accordingly, if one factor is deficient, the loss is very heavy. Perhaps the moisture factor is more often to be charged with the responsibility for poor returns than any other single deficiency.
We are told that 10 inches of rainfall in a year is sufficient for the production of successful crops under the methods of dry-farming. We are told that 20 inches of precipitation is sufficient for the production of successful crops under ordinary farm methods— provided it is well distributed throughout the year. Most places in the eastern states enjoy from 30 to 40 inches of rainfall a year. Nevertheless, there is hardly a season in which crops, and especially vegetable crops, do not suffer for lack of moisture during at least a month. The solution of this seeming paradox lies in the fact that our rainfall is poorly distributed through the growing season. We may have as much as 9 inches in a single month, and occasionally less than 1 inch. The total for three months in succession may be as low as 4 inches. Even such a condition as this does not frequently appear upon the weather records; for a period of drought may be followed by torrential rains sufficient to make up the average rainfall after the harm is done.
In view of these conditions, it is necessary that the vegetable-grower take measures to prevent the loss, through lack of sufficient moisture, of all the time and money that he has invested in land, tillage, fertilizer, seed, planting, cultivation, and care, to say nothing of the loss of the profit which he may reasonably expect. He may accomplish much by so managing his land as to conserve to the utmost the rainfall that is his. He may leave his land rough over winter to prevent runoff, he may harrow frequently till planting time, he may maintain an effective mulch throughout the season; even so through lack of rainfall—through absence of moisture to be conserved—he may lose his whole crop or so much of it that he might better have left the ground unplanted.
Within the past ten years, the possibilities of irrigation have become apparent to many vegetable-producers. They have found that the elimination of the moisture factor as one of the obstacles to successful crop-production has made possible larger yields, better quality and early maturity, with all the advantages in economy of management and in returns that accompany these gains. Irrigation has proved of especial value when sowings ore made in midsummer for autumn maturity, at transplanting time, and as crops approach harvest.
Surface irrigation is practised to a very limited extent in the East. The method consists in conducting water along the end of the plat to be irrigated and allowing it to flow into furrows between the rows of the crop. It is best to permit the water to reach the far end of the row as soon as possible and then allow it to be absorbed evenly throughout the length. If this is not done, the part of the field next the supply-ditch will receive much more water than the remainder. This form of irrigation is useful on level land where there is abundance of water and where the soil is suitable. Light soils drink up the moisture so rapidly that an even distribution of the water is difficult and uniform results may not be secured.
Boston gardeners employ hose in watering their plantations. A system of underground pipes is installed in such a way that 50 feet of hose will reach all parts of the block. The cost of installation for the first acre is reported in a Massachusetts bulletin as being about $65 and successive acres may be piped for approximately $50. An acre may be given 1 inch of water by one man using 1 ¼ -inch hose, in five or six hours. Hose irrigation is objectionable on account of the disturbance of plants, the danger of injury to the physical condition of the soil, the amount of labor, and the frequent replacement of hose.
Sub-irrigation is practised in certain districts of Florida and on some muck land areas in the North. In the Sanford, Florida, district, which is typical, the water-supply is from artesian wells. The land is underlaid with tile which is accessible at both its highest and its lowest points. Thus it serves for both watering and drainage. The impervious bottom which underlies the soil is essential for the successful operation of the plan. On the muck lands of the North, the object is accomplished by closing the drainage outlets and so raising the water-table that the surface soil is moistened. It is not good practice to keep the water-table high, because it inhibits the proper root-development of the plants.
Growers of vegetables in the eastern half of the United States are using various types of overhead irrigation far more than other methods. These systems usually involve the establishment of lines of pipe mounted on posts and carrying either sprinklers or small nozzles. These lines are so spaced that the ground may be evenly covered by the spray. Some types of sprinklers are so constructed as to revolve and cover an area of perhaps 25 feet radius. These are objectionable because they cannot cover the ground as evenly as other types.
More commonly employed are small nozzles which consist merely of a threaded plug of brass through which a straight hole is accurately drilled. These are set in holes in the pipe-line. Recently various modifications and improvements in these nozzles have been made. The nozzle line is screwed together and mounted on the posts, and a special machine equipped with a small level is used for tapping and threading the holes. The nozzle line is mounted with a union m which is set a handle for turning to cast water far to each side or to cover the near ground by throwing vertically. The nozzles are usually spaced about 3 feet apart and throw a fine solid stream which breaks at some distance from the opening. When the water reaches the ground, it is a fine mist similar to a light rain. Twenty-five to forty pounds of pressure is sufficient to cover a belt ranging from 20 to 30 feet on either side of the line.
A long line, of say 300 feet, would consist of 100 feet of 1 ź-inch pipe, 100 feet of 1-inch pipe, and 100 feet of 3/4 -inch pipe.
Nozzle lines are supported in many different ways. The consensus of opinion at present is that they should be about 7 feet above the ground to avoid interference with work that is being done. These posts must be set 15 feet apart to carry 3/4-inch pipe and a little farther apart for larger sizes. Posts of pipe or wood are most commonly used, but suspension from a cable supported by posts 100 feet or so apart is gaining in favor with vegetable-gardeners.
Occasionally, for temporary purposes, as for a single watering of young strawberry plants, the pipes are simply laid on the ground and turned by the handles in the usual way. Other growers have small horses which may be placed on the ground to carry the line temporarily. Mechanism has been devised by which a large number of lines may be automatically controlled from a single point, turning the spray constantly from one side to the other.
The main at the end of a field may be buried and the lines supplied through risers, or it may be carried on the first post of each of the rows which support the nozzle lines.
Comparatively few gardens are so located that a suitable supply of water is not available at reasonable cost. There are several possible sources. Some gardeners pump directly from streams or ponds, ordinarily using a gasolene engine and the triplex type of pump. In other sections, where the water-table is relatively near the surface, and where the ground-water is abundant, wells are sunk. Some employ a number of driven wells and gather water simultaneously from all of them. At Rochester, New York, many wells of large diameter with concrete walls are to be found. The method of sinking them is ingenious. A circular ditch of the desired diameter, say 15 to 25 feet; and about 2 feet wide and 4 feet deep is dug. In this is built by means of wooden forms a concrete ring. The lower edge of this ring is beveled outward at an angle of perhaps 30°. The ring is strongly reinforced and short bits of pipe are inserted radially. After the concrete in this ring has set and the forms have been removed, the work of digging is begun within. The earth is removed, one man seeing that it is taken evenly from the sides of the well under the sharpened edge. As the work progresses the ring sinks into the ground and radial concrete blocks are built upon it to serve as a wall. The well may be sunk to a depth of 20 or even 25 feet. The large diameter offers great gathering surface, and an abundance of water may be secured from a stratum that would not yield a sufficient amount by means of small wells.
Many gardeners in the neighborhood of cities are able to utilize the municipal water-supply, taking advantage of the low rates which are granted to large users. Some are able to procure water at a cost as low as 6 cents a thousand gallons. This is about as cheap as pumping.
Many questions arise as to the handling of irrigation- water. The practices have not been worked out nearly so fully in the East as in the West. Almost no well- planned experimental work has been conducted, and opinions among users vary greatly. Although a few prefer to apply water in small amounts and frequently, most seem to think that through irrigation is preferable. Most men water at night or when it is cloudy, but some do not hesitate to apply even in midday, thinking that the plants are benefited by the cooling. It is well so to plan the work that the ground will not be muddy at harvesting-time. With tomatoes, precautions must be taken against cracking. This is usually occasioned by heavy watering after the plants have been kept quite dry. Lettuce requires special care to avoid the development of rots of various sorts.
The use of irrigation-water does not relieve the grower of the necessity for good drainage or careful conservation of moisture. The former guards against overwatering or heavy rains which may come just after a thorough irrigation. The latter saves water, which is costly and keeps the soil in better physical condition.
Overhead irrigation systems are used to some extent for spraying, for the application of fertilizers, and for frost protection. In some cases the water is heated before it passes to the nozzle lines.
It makes little difference how perfect a system of irrigation equipment one may have installed, or how smoothly the pump works, or what a beautiful spray the nozzles throw on the crop if the returns are not sufficient to justify the outlay. This suggestion raises the questions of cost and of gain in market value of the crop. The first cost for equipping an acre is stated by manufacturers to be in the neighborhood of $125 to $150, making use of new pipe. Some men have economized in various ways and have achieved the desired result at lower cost, although many figures that are given are misleading because the very important labor of the owner in installing the system has been neglected.
It requires 27,152 gallons of water to cover an acre 1inch deep. This amount of water is applied through 1/12-inch nozzles at the usual spacings in eight and one- half hours. Water may be pumped ordinarily at 2 to 6 cents a thousand gallons.
Many growers can give very inspiring figures as to the results that they have secured by means of irrigation equipment. One well-known New Jersey grower is reported on first-rate authority to have secured twenty-five tons of beets to the acre and 620 bushels of potatoes from the same area. A crop of onions worth $1,500 has been taken off a 5-acre piece early enough to permit a later crop of Golden Self-blanching celery to be matured. Another grower reports that an outlay of $300 to $400 saved several thousand dollars worth of celery, whereas an unwatered acre and a half was a complete failure.
The Ontario Agricultural College reports experiments as follows: Non
Leaf June 22 July 4
Head July 10 July 20
Weight of crop—
Leaf 20 lbs., 5 oss. 11 lbs., 3 oss.
Head 25 lbs., 15 oss. 9 lbs., 1 01.
Quality Fine Bitter
At the outset it was pointed out that the heavy cost involved in making conditions favorable for crop-production renders it almost essential that vigorous measures be taken to prevent loss by drought. Now that the possibilities and advantages of irrigation have been indicated, it is well to emphasize the importance of making every other condition favorable. If every factor is favorable except the moisture factor and one other, and money is invested in irrigation, and the other factor prevents the maturing of a profitable crop, the situation of the grower is worse than before by the amount of his new investment.
An application of water equal to an inch of rain over an acre requires 27,152 gallons, as has been said.
To deliver this water, No. 1 Skinner nozzles with pressure of forty pounds should be placed 4 feet apart in the line and the lines should be 56 feet apart; nine hours and twenty-three minutes at forty pounds pressure is the time required. The discharge for each nozzle is 24.1 gallons a minute.
Ninety-four and two-tenths feet of elevation gives forty pounds pressure.
A four horse-power gasolene engine and duplex pump will deliver approximately 100 gallons a minute at thirty pounds pressure, at a cost of roughly 10 cents an hour.
A 2 ½ -inch pipe will deliver 100 gallons a minute at a distance of 100 feet, and a 3 ½ -inch pipe is required for distances between 500 and 700 feet.
With No. 1 outdoor nozzles, a nozzle line 150 feet long may be composed entirely of 3/4-inch pipe.
A line 250 feet long needs 100 feet of ¾ inch and 150 feet of 1-inch pipe.
A line 700 feet long needs 90 feet of ¾ -inch, 160 feet of 1-inch, 175 feet of 1 ¼ -inch, 175 feet of I ½ -inch and 100 feet of 2-inch pipe. Paul Work.