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

by Gustavus A. Eisen

—The subsoil in a raisin vineyard is of great importance. Properly irrigated soils, if they are sufficiently rich, need not necessarily be very deep, as the raisin grapes, especially the Muscat, seldom extend deeper than eight feet below the surface. Even from four to five feet of rich soil may be considered as enough in irrigated vineyards, where the water is abundant. In poorer soils, or in districts with less irrigation, the roots of the vines penetrate much deeper, and the importance of the subsoil in such cases is apparent. Any rich subsoil will serve our purpose. It is always best to thoroughly investigate the subsoil before the vineyard is planted, and in doing this the following points must be considered: The subsoil should be as rich as possible, and there should, in no instance, be less than four feet of rich top soil. Very sandy soil or pure sand is not a proper subsoil for raisin grapes. Such soil will cause the top soil to dry too quickly after each irrigation, and will cause the top soil to leach out, while it besides gives no nourishment to the vines. Hardpan is not desirable, not even admissible, except in places that are or will become subirrigated. Alkali or salty subsoils will soon spoil the quality of even the best top soil. This especially is the case in irrigated districts, where the salts of the subsoil are carried to the top by the rising waters or by the continued irrigation. Hardpan which readily dissolves when wet is not injurious.

Hardpan Soils.

—While I have alluded to them already, a few more remarks on these soils are here in place. The hardpan consists of a stratum of hard soil or hard rocky substance below the top soil. The depth at which the hardpan is found varies. In places where it is situated eight or ten feet below the top surface it does but very little harm, and may even prove beneficial in localities where water for irrigation is scarce, as it checks too rapid drainage. If the hardpan is situated closer to the top soil, it may seriously interfere with the vines, and if too close, or say within two or three feet from the top, it makes such soils entirely unfit for raisin grapes. If situated somewhat lower down, say from four to six feet, the hardpan does no great harm in subirrigated districts, while, in places where irrigation is not used, it leaves the top soil too shallow and too dry. But allowance must always be made as to the nature of the hardpan. Some varieties of hardpan are so hard that they can best be compared to regular stratified rocks, impenetrable to the roots of the vines, and impervious to water. Other hardpans again are softer, and allow the vine roots to penetrate more or less readily, while some again are so soft that they dissolve in water and make good soil for the vines. If the hardpan is very shallow, it may pay to blast holes through it, in order to allow the roots of the vines to penetrate to lower soils. But if the hardpan is thick and hard, and if there is no immediate prospect of subirrigation, it is better to use such land for some other purpose than for raisin-vines, which will only pay properly if grown under the most favorable circumstances, and on the best and deepest soils.

As to the nature of the hardpan, a few remarks may prove of interest. The hardpan can best be compared to a stalactite formation similar to those found in various caves. It has been formed very much in the same way as they were. In caves the rainwater, that seeps down from the top surface, dissolves various substances, especially carbonates (and silicates even) which again are deposited on the underside of the cave roof. This precipitation of hard material is caused both by evaporation of the water, as well as by attraction and adhesion. Such redeposition of dissolved minerals is seen for instance if solutions of salt in water are passed through tasteless and clean sand. The water will come through sweet and tasteless, the salt having adhered to the surface of the sand grains. Similarly, if a hole is dug near the seashore in the sand, the salt water will seep through, and form a well of more or less tasteless drinking water. In the formation of hardpan, this is exactly what has taken place. The rainwater has dissolved certain elements, such as carbonates of lime, or carbonates of sodium and various other salts, and in its way through the lower strata of the soil these dissolved elements have again been taken up by the sand and cemented it together. Thus it is explained why hardpan upon examination is so often found to resemble sand or sandstone: the lower sandy strata of the soil have been especially effective in causing the lime in the water to adhere to the numerous surfaces of every individual grain of sand. In hog-wallow districts the hardpan is found principally between the individual hog-wallows, but rarely in or under them. The rainwater has here carried the minerals in the soil to the deeper places between the hog-wallows, in which it has accumulated to a greater extent than anywhere else, and thus formed a heavier hardpan. In flooding the hog-wallows, the top of every hog-wallow is seen to settle and fall in, there being no hardpan below it, if the sides of the hog-wallow are steep. Where the hardpan consists principally of lime compounds, its chemical composition is not detrimental to the vines. But where the hardpan is cemented by alkalies more or less soluble in water, these deleterious substances will dissolve and rise to the surface to the great detriment or even to the total destruction of the vineyard.

Comparative Value of Soils.

—The river bottom soils, or soils formed by the deposit of creeks, are with few exceptions rich and deep, and contain in abundance all the elements necessary to produce a superior Muscat grape. Such soils are, however, often injured by subsoils containing mineral deposits, which will injure the vines, or by hardpans, which will cause the soil to dry out. Poor soils will not prove profitable, and rather than plant vines on such soils it would be better to plant no vines at all. The rich soils are not only the heaviest producers, but the vines grown on them are stronger and healthier and in every way better able to resist the attacks of insects and fungi and the ravages of other inexplicable diseases. But regardless of these advantages the various soils leave their effects on the grapes, some of them producing sweet and very keeping raisins, while others cause large berries and bunches, which bring the highest market price. Thus the lighter and drier soils produce richer flavored and sweeter raisins than the wet and rich soils, which again produce the largest and handsomest grapes. On the latter soils the raisins when cured will be found to be dark and covered with a heavy bloom, while the raisins from the sandier or gravelly soils are lighter in color and with less pronounced bloom. The keeping quality of the raisins from gravelly soils is well known. In California the keeping quality of the raisins is seldom inquired into, as our raisins keep remarkably well and are in this respect superior to those grown in Spain. This may be from the effect of our drier climate more than from any certain quality in our soils.

As a rule it may be said that poor soil causes the raisins to mature earlier than the rich, heavy loams, and on this account the latter are to be greatly preferred, as the earliest raisins in any district are never as good as the bulk of the crop, and are in demand rather as a curiosity, and for the purpose of supplying an early market, than through any superior qualities. In some districts there is such a great difference in the time of ripening upon the various soils that the grapes grown on the earliest soils are used only as table grapes fresh. In planting a raisin vineyard, the future profits depend upon the choice of land, and it is far better to pay a high price for the best land than to take the inferior land as a gift. Few of those who now enter upon raisin culture take the proper care in selecting the land, neither do they sufficiently, if at all, realize the advantages of the rich soil, nor the disadvantages of the poor land.

Alkali Soils.

—While nothing but first-class land is to be recommended for raisin vineyards, and alkali lands are of all soils those least suitable for our purpose, still a consideration of these lands will interest many raisin-grape growers. The best lands for raisin purposes in California are often contiguous to alkali lands, or to land containing more or less traces of alkali. A vineyard on the best soil contains often spots charged with alkali, and it may be inconvenient for the grower to allow these spots to lie idle, and he would prefer to fill them up with vines. The first work must then be to get rid of the alkali or reduce it to such an extent that it will not prove injurious. The general alkali lands are classed in three kinds, according to the quality of the alkali.

1st. Alkali salts, such as carbonates and borates. These are greatly detrimental to the vines, and no vines could be expected to do well in such soils, as even the smallest percentage of this alkali is injurious or even ruinous to the crop. In clayey soils these alkalies cause the clay to harden in such a way that no good tilth can be obtained. The land may be plowed ever so much, it will only turn up in chunks and never become properly pulverized. These true alkali salts consist principally of carbonate of sodium (sal-soda) or of carbonate of potassium (saleratus). Remedies: Gypsum, land-plaster or leaching with water.