The Raisin Industry / A practical treatise on the raisin grapes, their history, culture and curing

by Gustavus A. Eisen

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.