Soils, their formation, properties, composition, and relations to climate and plant growth in the humid and arid regions

by Eugene W. Hilgard

Deciduous Orchard Trees.

Among deciduous orchard trees, strangely enough, the almond stands alongside of the fig in alkali-resistance, as indicated in the table. The peach seems to be much more sensitive, ranking near the apricot and prune, whose tolerance is less than half as high. That the pear and apple, generally counted among the more northern fruits in the humid region, should excel these stone fruits in endurance of alkali, is rather unexpected; and the figures concerning the whole group of these rosaceous fruits admonish us that it is unsafe to predict, without trial, what may be the outcome of culture tests. Thus plum trees, apparently in good condition, sometimes suddenly begin to fail when starting to bear; the fruit appears normal on the outside for a time, but the pit fails to form, being at times flattened out like a piece of pasteboard; and the fruit does not mature. Yet there is no observable injury to the base of the trunk, or to the roots. On the other hand, pears do well even when the outside bark around the root-crown is blackened by the action of the alkali salts. But 38,000 pounds, even of sulfate, proves too much for the pear.

The quince appears to be materially more resistant than the apple or pear. It probably ranges alongside of the fig, the soil-adaptations of which it shares in other respects also.

The English walnut resents even a slight taint of black alkali; but is fairly tolerant of “white” salts, as is shown in the peculiarly suitable light loam soils on the lower Santa Clara river, in Ventura county, as well as in Orange county, California.

Close figures for the limits of alkali tolerance in the case of deciduous orchard trees cannot easily be given or determined, owing to the difficulties inherent in the differences of root penetration in the several soils and localities; as well as the fact already alluded to, that in close-textured soils the tolerance is in general decidedly less than in sandy lands. Hence the figures in the table must be taken as more nearly representing relative tolerances, rather than absolute data to be applied in every case. As regards the stone fruits, it should be remembered that the Myrobalan root, being at home in Asia Minor, where alkali abounds, should when practicable be used wherever alkali conditions exist, in preference to all but the almond, which seems to resist well, even on its own root, but has not as wide a range of adaptations as a grafting stock as the myrobalan. While most of the other stone fruits at the Tulare substation were on myrabalan roots, the stock of those in outside orchards was mostly in doubt. It is also to be kept in mind that different varieties of the same fruit—e. g., pears and apples—show a not inconsiderable variation in their resistance.

Timber and Shade Trees.

Of trees, forest and shade, suitable for alkali lands, some native ones call for mention. One is the California white or valley oak (Quercus lobata), which forms a dense forest of large trees on the (almost throughout somewhat alkaline) delta lands of the Kaweah River in California, and is found scatteringly all over the San Joaquin Valley. Unfortunately this tree does not supply timber valuable for aught but firewood or fence posts, being quite brittle.

The native cottonwoods, while somewhat retarded and dwarfed in their growth in strong alkali, are quite tolerant of the white salts, especially of Glauber’s salt. As they usually grow near to the water, their tolerance for alkali salts is difficult to ascertain.

Of other trees, the oriental plane, or sycamore, and the black locust have proved the most resistant in the alkali lands of the San Joaquin Valley; and the former being a very desirable shade tree, it should be widely used throughout the regions where alkali prevails more or less. The ailantus is about equally resistant, and but for the evil odor of its flowers, deserves strong commendation.

Of the eucalypts, the narrow-leaved Eucalyptus amygdalina (one of the “red gums”) and the closely related viminalis, seem to be least sensitive, and in some cases have grown in alkali lands as rapidly as anywhere. The rostrata, as well as the pink flowered variety of sideroxylon, are now doing about as well as the amygdalina at Tulare, where at first they seemed to suffer. The common blue gum, globulus, is much more sensitive.