IRRIGATION.
Introductory Notes.
—The irrigation of the raisin grapes was, for several years, considered as a practice entirely peculiar to California, but as our knowledge extended it was found that, far from being anything at all new, it had been practiced successfully for centuries in some of the Mediterranean countries. We have already mentioned how irrigation is customary both in the Valencia and Denia districts, as well as in Greece. It is evident that irrigation there is only limited by the supply of water, and that there is no question about its usefulness. As regards the methods of irrigation in these foreign countries, we beg to refer to the [chapters] treating of these countries. Here our efforts shall be to consider irrigation in its relation to the following points, which are of more general interest to the Californian growers: Necessity of irrigating the raisin-vines; the health of irrigated vines; the bearing quality of irrigated vines; the quality of the irrigated grape; supposed unhealthiness of irrigated vineyards; irrigation by flooding; irrigation by furrowing; subirrigation; seepage; drainage; irrigation and its influence on the soil.
The Necessity of Irrigating the Raisin-vines.
—When the irrigation of raisin grapes was first attempted in Fresno and Riverside, hardly any one was acquainted with or knew that irrigation had ever been used for such a purpose before, and irrigation was considered as a venture which did not promise well for the future. Later on it was found that the raisin grape really would grow and do well in some localities without irrigation, and the latter practice was accordingly condemned. To-day, however, the practical knowledge of irrigation is greater and more generally distributed, and it is now fully understood that irrigation is not only not injurious, but beneficial and necessary in localities where the raisin-vine will not grow or bear sufficiently without it. The questions then arose, When is irrigation necessary, and how much irrigation is required? The first object in raisin-growing is the profit; a secondary object is how to so treat the vines that they will last as long as possible. To attain the first object, we must raise plenty of grapes, and when a larger quantity of good raisin grapes can be grown with irrigation than without it, irrigation is justifiable and necessary. In Spain, especially in the Denia district, irrigation of the raisin grapes is practiced wherever water can be had, and the same is the case in Greece and Italy.
In California the tendency is now to irrigate wherever water can be had, and wherever it is profitable to procure it. In Fresno, Tulare and Kern counties, raisin grapes could not be grown without irrigation. These same conditions are also found in San Bernardino county, while in Los Angeles and Orange counties all the best vineyards are irrigated, and only occasionally do we find the conditions such that irrigation is not absolutely necessary. In Northern California, raisin-vines may be grown without irrigation, but the latter is considered of such advantage that expensive pumping works have been erected in places where no other means were had for irrigating the vines. In San Diego county, especially in El Cajon and Sweetwater valleys, irrigation is not absolutely necessary, in fact it is not practiced there at all, although water could be had, but as a consequence the crops there are not as large. In Smyrna, in Asia Minor, the largest raisin center in the world, the raisin-vines receive no irrigation, but the unusually heavy rainfall of this section makes the want of irrigation less felt. Of course, outside of the raisin districts proper, Muscatels or other raisin-vines may be grown, and are grown to good advantage without irrigation, but the climate in those places is generally unsuited to the drying of the grapes.
Should we inquire into the reasons why raisin grapes may in some localities be grown and actually prove profitable without irrigation; we find the same to depend not alone upon the rainfall of the locality, but principally upon such other circumstances as dew, fog, the nature of the subsoil, and the moisture of the air. In Smyrna the rainfall of the wet season is from twenty-four to thirty-six inches annually, and greater than in any other raisin district. In El Cajon the rainfall is only half that much, and the moisture in this case must be sought partly in the subsoil, which is especially retentive of moisture, as well as in the dew, and the warm fogs from the ocean. The subsoil has the greatest possible influence, as in other valleys near by, where the fog and the dew are the same, but, where the subsoil is different, no raisin grapes can be grown without irrigation. Malaga is in this respect very similar to El Cajon and Sweetwater valleys, but it enjoys more rainfall than the latter places, while probably the dew and fog is about the same. Still in Malaga irrigation is used in a few isolated localities where it can be obtained, the nature of that country being such, that no general irrigation system is possible, and this is probably, more than anything else, the reason why the vines are not more generally irrigated there. In Chile, in the valley of the Huasco, the Muscat vines are grown both with and without irrigation, the conditions there appearing to be very similar to those of El Cajon valley in San Diego county. From the above we might draw a general conclusion, that wherever the raisin-vines cannot grow without irrigation, and wherever water can be had in sufficient quantities, irrigation is practiced in order to increase the crops and to make the business more profitable.
Health and Longevity of Irrigated Vines.
—As regards the health of the vines, the old idea in this country that vines would suffer from irrigation is decidedly erroneous. The vines of Denia in Spain have been irrigated for eighty years or more, and are to-day the healthiest vines in Spain. Similarly, the Fresno vines, where the water level, as in Denia, is only from five to ten feet below the surface, show no signs of decay, while many of the raisin-vines in other parts of the State, especially where planted on the hillsides, show diseases which baffle the cultivator. I do not, of course, mean to say that irrigated raisin-vines are entirely free from diseases, but only that, so far, the healthiest and strongest raisin-vines of the world are those which are irrigated, and which have always been irrigated. Of course in this respect the Muscat grapes, as well as the currant vines, differ materially from certain wine grapes, which as a rule have originated on drier soils, and which, if grown with irrigation, deteriorate and yield inferior fruit. The raisin-vines require much moisture, and, if this is not supplied in one way or another, they will suffer and prove unprofitable. The same is observed in soils which rapidly lose their moisture. In such soils the Muscat is not at home, and its health and vigor is seriously impaired.
The Bearing Quality of Irrigated Vines.
—In regard to the bearing quality of the raisin grapes under irrigation, we know with certainty that the irrigated raisin-vines yield by far the most. In Valencia and Denia, the vines yield from five to ten tons to the acre, and so do those of Riverside and Fresno, while the El Cajon unirrigated vines yield only from one to two tons per acre. If the latter place would irrigate judiciously, its Muscat vines would no doubt bear as well as those of any other locality. I am led to this belief from what I have seen of irrigated grapes elsewhere in San Diego county, which were fully as well loaded as the heaviest vines in San Bernardino county or Fresno.
Quality of Irrigated Grapes.
—That the quality of the irrigated raisin grape is increased by judicious irrigation is readily seen in all irrigated districts, where those vines which receive their proper share of water produce the largest bunches and berries. But it is also evident that too much water will cause a deficiency of sugar in the grapes, as well as a lack of flavor, by which the irrigated grapes can always be distinguished from those grown with natural moisture. Grapes too freely irrigated are not alone wanting in sugar, but also in color. Such grapes remain green to the end of the season, and never assume that amber color so valued in grapes, and which always indicates beforehand what raisins they will produce when properly dried. In our interior valleys, where the sun and the wind sometimes produce sunscald of the berries, which again causes them to fall off or dry up long before they are properly ripe, this defect is much more frequent on vines which suffer from want of water than on those which have had enough. When the soil is not subirrigated, it is therefore advisable to irrigate the vines at the end of June, just before the hottest part of the summer arrives. Similarly, irrigation will help to swell out the berries if applied just before they commence to ripen.
In conclusion we might with truth say that the raisin grapes may in many localities be grown without irrigation, but that in California, in Greece and in Spain, the largest and most prosperous districts are those where the raisin-vines are liberally irrigated. The Muscat grape seems especially to love water, and, in the real raisin districts, the healthiest vineyards are those that are best irrigated. The berries and bunches are also increased in size, but not in flavor and aroma, by irrigation. In places where the raisin grapes will not bear without irrigation, the latter, of course, is a necessity. There are always naturally subirrigated parts, in every county or district, where artificial irrigation is not required. But these parts are generally confined to river bottoms or to natural sinks, which, so far, have played no important part in the raisin industry. Considered from a practical standpoint, irrigation of the raisin-vines is necessary in California, and, should it from some reason or other be made impossible, the raisin industry would not prove profitable or even possible, except in a few very limited localities.
Much has been written in regard to the supposed unhealthiness of the irrigated vineyards. The malaria prevalent in some vineyards is no doubt caused by irrigation; but it has been amply proved in Fresno and elsewhere that if the grower would know from the beginning how to so prepare his land that there would be no stagnant pools, no waste water, and no swampy grounds, the so much talked of malaria would be as rare in the irrigated vineyards as anywhere else. It is not the irrigation that causes malaria, but the waste of the water, the carelessness of the irrigator and the faultiness of the badly constructed irrigation works. After the vineyard has been irrigated a few years, the malaria leaves it entirely. This is the experience in Fresno where the vineyards, after years of irrigation, have become perfectly healthy.
Various Methods of Irrigation.
—There are several methods of irrigation now practiced in the irrigated vineyard districts. We may irrigate by flooding the land or by leading the water in furrows between the vines. Both ways, but especially the former, may, if continued long enough, cause subirrigation, the most desirable state of irrigation. The choice of methods of irrigating does not always lie with ourselves, but depends upon the quantity of water at our command, the lay of the land, etc. Sometimes one method will in course of time give room to another, and again, after the lapse of a few years, continued irrigation may not be necessary or desirable.
Irrigation by Flooding.
—This method consists of flooding the land either by means of checks and banks, which must have been constructed before the vines were planted, or in simply flooding ground which is naturally level. In either case the land must naturally not be too rough, and the water must be abundant, else this method cannot be used. It will always pay to engage the services of an engineer in preparing such ground for vines. The extra cost will be more than paid for in the first few years, when frequent irrigations of the vineyard are as necessary as they are expensive. The ditch supplying the vineyard should always run on the highest ground, and in no instance should it be run through low ground when high ground can be had, as the low ground may in the future have to be used for drainage, about which we will treat further on. From the main canal, branch ditches should run out at right angles if possible, or if the ground is very uneven they may follow the highest parts. The ground between these ditches should be properly leveled into checks. With checks the irrigator simply measures a piece of ground of any size which is surrounded by a levee or bank. This bank must be high enough to allow the water to cover all of the ground as soon as the check is filled with water from the ditch.
To make the ground level enough, it is generally necessary to level it with scrapers. The more level is the surface the better, cheaper and quicker will be the irrigation, and no small amount of trouble will be avoided if this work is properly done before the vines are planted. Too little of this leveling is done in some places, and I have seen thousands of acres planted in Muscat vines which were so improperly leveled that the profits of the vineyard in after years would be seriously interfered with. To understand how this can be possible, we must remember what takes place when we irrigate and after we have irrigated. The gate in the ditch is opened, the water flows out and runs immediately down to the lowest part of the check. When this part is reached, the check begins to fill up. If the ground is very uneven, it may take days to fill the check, and the lower part will require to be covered several feet with water before it will reach the higher parts, which always need irrigation the most. To back it up so high requires also a correspondingly high levee, which again is more apt to break and cause trouble and expense the higher it is. After the water has reached the highest possible point, the flow is shut off, and the water begins to subside. The highest part of the land becomes dry the first, and quickly, while it may take days or even weeks to dry up the lowest part of the check. When at last the check is all dry it may be found that the lowest vines have been injured or entirely drowned out. When summer irrigation is used, it is absolutely necessary to have the ground level, so that when it is flooded the water will not reach up to the grapes, as they spoil when coming in contact with the water.
The time when flooding should be used must depend upon circumstances. As a rule, flooding is especially adapted to winter irrigation, as, when the vines are entirely dormant, they may be submerged for months without suffering any harm. Young vineyards may also be flooded in summer time, but, when the grapes begin to appear, flooding can only be done in the winter or when the land is absolutely level, but even under the most favorable circumstances many grapes are always lost. Some have so prepared their vineyards that a check, when flooded, can be drained into a lower check or into a ditch. This is a very good arrangement where the land is not entirely level, as it will cause the low places to dry up as quickly as possible. But a better way is to have the ground so level that the water will sink evenly and leave no sinks nor any high and prematurely dry places. There are, however, soils so composed that the water cannot sink through them in any reasonably short time. Such heavy soils must be surface drained after every flooding, or perhaps had best be given up to some other method of irrigation. But such hard or impervious soils are frequently improved by irrigation, and in course of time lose their impervious nature and become subirrigated. If the land is tolerably level by nature, and there are prospects of subirrigation soon appearing, it may be unnecessary to level the land, and flooding with temporary checks may be used with advantage for the first few seasons. Furrowing will generally assist this mode of irrigation.
Irrigation by Furrowing.
—This method of irrigation is practiced where the land is not sufficiently level to be flooded, or when the water is not sufficient to enable the irrigator in a short time to flood the land. The practice of furrowing simply consists in plowing furrows alongside of the vines, and then to lead the water in the furrows. This system is by far the one that is most practiced in Southern California, as it has some advantages over the flooding; it is, however, not so effective and cannot supply the vineyard with as much water as flooding. To use the furrowing system to advantage, the land must have been previously leveled, but not necessarily graded to an absolute level. It is enough to have the surface smooth and on an even grade, in order that the water may run from a higher point to a lower one without spreading or breaking out. Especially all knolls in the vineyard must be leveled off, and care must be taken to fill all hollows or sinks in which the water would otherwise collect.
After the vines are planted, or when irrigation is necessary, one or more furrows are plowed on each side of the vine, and the water is allowed to run in them for several hours, or even days, until the soil is sufficiently soaked. In many places three furrows are made between the rows of vines, and the water is allowed to run in at one end and out through the other in a stream only sufficiently large to cause all the water to sink. Where particular nicety is required, the waste water which runs out at the farther end may be collected in a trough with perforated holes, through which it is conducted to a ditch or lower check. Similarly, a long trough may be used for conducting the water to the land in the first instance, and allow it to run out through a number of small holes, one of which is situated in front of every furrow. When the ground is well prepared, level and with an even slope, this system of irrigation is very perfect, and causes but little expense and trouble in management. In Riverside the vines are irrigated thus every three or five weeks, while in Redlands less irrigation is used on old vines. As a rule, in Southern California the furrowing system is the accepted one as being best adapted to the nature of the country. The water is conducted both in open ditches and in pipes, and when under pressure saves much labor and expense which would otherwise be required for the continued construction and repair of ditches.
The furrowing system has, however, its disadvantages. It requires a longer time to fill the soil sufficiently, and accordingly it takes many more irrigations to accomplish as much as with flooding. As advantages of this system, we might state that it requires no banks or levees to back up the water, and a vineyard irrigated this way can be kept entirely free from weeds by a few cultivations, while a checked vineyard must besides be cleared with hand labor, as the banks and checks are apt to be destroyed by cultivation.
Subirrigation.
—Subirrigation may be either artificial or natural. The artificial subirrigation has, as far as I know, only been used in a few vineyards in Yolo and Solano counties, the report, shortly after it had been established, being very flattering as regards its success. But of late years we have heard nothing about this kind of irrigation, and it is likely that some practical difficulty was encountered which could not be fully overcome. The artificial subirrigation consists in laying larger and smaller cement pipes between the rows of the vines. These pipes are perforated in various places, and, when filled with water under pressure, the water runs through the perforated holes and keeps the ground outside the pipes constantly moist, without causing the surface of the soil to get wet and weedy, and herein consist the principal advantages of the system, as well as in the fact that rolling ground can be irrigated thus without being previously leveled and without being cut up with open ditches. The difficulty of keeping the holes open and of preventing the roots of the vines from entering the pipes is, I understand, very great and probably impossible to overcome. Both irrigation water and liquid manures could by this system be supplied to the roots of the vines directly without any waste, and, in cases of diseases or attacks by underground pests, medicines or insecticides could be brought to the soil with the least possible cost.
The natural subirrigation is caused either by the whole soil filling up with water from the natural and original water level to the very top or to the roots of the vines, or from an impervious hardpan or clay, as subsoil, up towards the surface. As an example of the former we might cite the country around the irrigated plains of the San Joaquin valley, especially around Fresno and in Mussel Slough. Before irrigation was begun there in 1872, the surface water was from sixty to seventy feet from the top east of the railroad, and from forty to fifty feet west of the railroad, lower down in the valley. After five years of irrigation it began to be noticed that the soil required less water. The water in the wells began to rise, and the following year the water stood in many places near or on the top of the surface. Now the whole irrigated district around Fresno has filled up with water to such an extent that drainage ditches have become necessary in some places in order to lower the water in the wet season some four or five feet from the surface. Many more drainage ditches will be required, as in wet winters the surface water in places is not only very near the top, but actually forms ponds or swamps where formerly the ground was entirely dry.
In the old irrigated districts, water can now be found at from six to ten feet in the driest season, while formerly the wells had to be from fifty to seventy feet deep. In the older vineyards, and even in many of the younger ones, no more surface irrigation is used; all that is now required is to allow the water to run in the main ditches, in which the water sinks sufficiently to keep up the supply of the evaporation of the ground outside. Large tracts of land which have never been surface irrigated are now sufficiently moist to grow vines to the greatest perfection, and many of the best vineyards have never been irrigated at all; in fact, nothing but drainage ditches have ever been made on the land. Whenever such subirrigation exists, the water level will be found higher in the winter than in the summer, and drainage should accompany subirrigation in nearly every instance. A subirrigation like the above exists in Denia and other of the Spanish districts. Subirrigation may be also caused by either impervious subsoils, such as hardpan and clay, or by spongy subsoils, which keep the water like a sponge. Such is the case to a limited extent in parts of San Bernardino county. At Redlands, for instance, much less irrigation is now used than when the vines were first planted, and this fact is attributed to a spongy subsoil peculiarly retentive of water. A similar subirrigation exists in the Mussel Slough country, where the water rapidly fills the land and keeps it moist throughout the summer. The phenomenal moisture of the El Cajon land is probably also produced by some kind of subirrigation, either on impervious or through retentive strata; the waste water from the surrounding hills no doubt supplies much of the water appearing in the lower lands of the valley. Other valleys close by do not show this moisture, the underlying strata probably making subirrigation impossible with the present amount of rainfall.
Seepage.
—Seepage is the quality of the soil to attract moisture and retain it. Seepage soils attract the water from a ditch run through the land, the water spreading all through the soil towards all sides instead of sinking only vertically down. There is a distinct difference between such seepage soils and those that do not seep, although there is a gradation in the degree of the seepage, some soils seeping more than others. Thus the Fresno soil, or the soils on the Fresno plains, especially the red and sandy soils, do not seep or percolate. Vines planted on the sides of the ditches, or a foot or two from their banks, will die and dry up if not specially irrigated by bringing water to their very roots. Other soils, especially the river-bottom soils or the alluvial soils, seep or percolate in a great or less degree. They act like a sponge, attract water and give it away slowly, and the soil will be found wet for long distances from the ditch. This seepage capacity of the soil is partly caused by an abundance of humus or vegetable matter. The seepage capacity of the soil greatly increases by admixtures of green vegetable matters through the plowing under of green crops, such as alfalfa, peas, beans, grain, etc. The value of seepage soils is seen especially where some uneven ground is scraped off and the top soil removed to low places. Such ground often becomes useless for years afterwards, especially if the quantity of humus in the lower soils is small. Frequent irrigations will not serve to keep such soils moist, as the water sinks rapidly down, leaving the poor top soil dry. Vines planted in such places never do well, and even heavy manuring will not suffice to bring on a strong, healthy growth. Such humus-wanting soils must be treated with green crops, as stated above, in order to become fertile and moist. Thus seepage and subirrigation are often confounded. The former is caused by the retentive and communicative quality of the soil, while the latter is caused by the natural or artificial distribution of the underground water.
Subirrigation and seepage combined make the most perfect irrigation for a raisin vineyard, with advantages that can in no other way be attained: absence of distribution ditches, which take up valuable land and which cost money to keep clean from weeds; less growth of weeds on the surface of the ground; greater mellowness of the top soil and less work in plowing generally; a greater and more uniform supply of moisture, which, instead of being near the top of the ground, is accumulated deeper down, thus causing the roots to go down instead of spreading near the surface; no expensive irrigation, which will require plowing every time after the water is spread on the surface; a greater coolness of the ground and a lower temperature generally, which shows itself in a more vigorous growth of the vines, a greater supply of grapes and less danger from sunburn. These and many more are the advantages of subirrigation and seepage combined. To attain them in a raisin vineyard, no labor and reasonable cost should be spared.
Raisin-grape Picking at Riverside.
Drainage.
—Drainage is necessary in all vineyards where large quantities of water are used for irrigation, and principally at the very time that subirrigation begins. Thus in Fresno county the best raisin vineyards are those in which the land is both subirrigated and drained. When irrigation commences in any certain district, no one thinks of drainage as a possibility, and great carelessness is shown in locating ditches and other irrigation works. But in a few years, when the soil is full of water which finds no outlet, drainage becomes both necessary and desirable. A very successful and highly necessary drain has been constructed through a part of the Fresno district, which so filled up with water during the rainy winter of 1883-84 that much of the ground could not be plowed until late in the spring. The drain remedied the evil and drained the soil, and the vineyards grown there are now counted among the best and most profitable. The water thus drained off lowered the water level from six to seven feet. In very dry seasons this ditch is filled with water, and serves then to keep the soil moist through seepage or subirrigation.
The Influence of Irrigation on the Soil.
—It is by many considered that irrigation helps to fertilize the soil. The spring and flood water contain great quantities of mud and humus, which when spread over the land will greatly increase its fertility. Even ordinary river water contains salts and other ingredients, which will fertilize the soil to no small degree. Another cause of the increased fertility of subirrigated soils is that the water which constantly evaporates carries with it salts, etc., from the lower strata up towards the surface, and makes them accessible to the roots of the vines. But, on the other hand, if the water or the soils contain alkalies or other destructive substances, these also are deposited on the surface to the great detriment of the vines, and often to such an extent that the vines will die or become sickly. Too abundant flooding may also leach out of the soil its soluble salts, and carry them deeper down in the ground. But if this soil after a while fills up with water and becomes subirrigated, the evaporation of water from the surface will gradually carry these salts back to the surface, when they will increase the fertility of the soil. Where drainage is very perfect, constant irrigation will gradually rob the soil of many of its soluble salts, and carry them to places where they will forever be out of the reach of the vines. To ascertain these facts and conditions, every vineyardist should have the soil analyzed about every five years, and too great care cannot be taken to keep the soil of proper strength.
Another influence of irrigation on the soil may also be mentioned here. Some of the soils in the irrigated districts which were formerly very hard and difficult to work have in course of time changed and become mellow. The water has undoubtedly caused a chemical and mechanical decomposition of the components of the soil, which has caused it to continually improve. Even certain kinds of hardpan have been known to dissolve when irrigated, and to change into useful and mellow soil, in which the vines can find nutriment. Such hardpans are those which are generally found in very dark red soils; those in lighter soils are not so readily dissolved.