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CROP SAFETY ON MOUNTAIN SLOPES.
By J. CECIL ALTER,
Observer, United States Weather Bureau.
When "Jim" Bridger, the pioneer Indian trader, told Brigham Young and his Mormon immigrants that farming could not be practiced in the Rocky Mountains, and that he would "give one thousand dollars in gold for the first bushel of wheat raised in the Salt Lake Valley," he evidently had in mind the mountain blizzards that lash themselves about the cloud-hemmed peaks and the desert-dry slopes and plains whose very vegetation—the characterless weatherworn sage-betokens extreme summer temperatures in certain districts and severe winter cold in certain other mountain regions.
But Colonel Bridger was not a true prophet, for to-day, while there certainly are numerous superheated deserts and overexposed slopes imprisoned in the Rocky Mountain fastnesses, where even native animals sometimes perish from exposure to the weather, there are many notable agricultural and fruit districts in the neighborhood of three-quarters of a mile above sea level that have climates of rare equability and gentleness, with an ideal progression of the seasons, where floriculture, horticulture, and agriculture are intensively and quite successfully practiced.
MOUNTAINS AS AN AGRICULTURAL ASSET.
These favored regions in many instances are on the lower slopes of mountains whose peaks dwell in almost eternal winter, and yet the fierce climate aloft does not descend upon the fields at the mountain's foot even in winter; and, as we become familiar with the conditions, we begin to comprehend the interesting fact that mountains, having certain favorable configurations, are actual assets to the farmer as weather producers and regulators, and form unique protection against the vicissitudes of climate so often found where elevation above sea level tends to expose the land.
The level farm on a level plain is exposed to conditions of winds, storms, and sunshine that are normal for that general latitude and longitude, but in the mountains the sun's rays glance about on the various slopes, collecting in one place and scattering away from another; and the winds and storms are prevented from sweeping over the agricultural valleys in unbridled frenzy by the protecting mountain barricades. Thus there are mountain lands that are totally unfit for agriculture by reason of severe climatic conditions, while only a few miles away will be found the choicest of lands in the finest of climates, depending for these especial characteristics or peculiarities on the way the sun's rays fall on the surface of the land in the daytime, and the way the surface air flows or drains over it at night.
ESSENTIAL FEATURES OF MOUNTAIN FARMS.
The land must be sloping, but it must slope in the right direction and at the proper angle; it may incline toward the farmer's homestead, or away from it if that seems more desirable; it may slope. evenly and gradually away from the lines of irrigation ditches, or, if it be an arid farm, it may slope gently away from the snow-laden hillsides in a very advantageous manner; and it may even slope downward to market by a good and easy road; yet more important than all these slopes is the inclination in the right direction with relation to the sun's rays and to adjacent canyons and drainways for the higher mountain air.
Primarily these subtle slope influences are entirely good, for it is by virtue of them that the mountain-locked valleys are vigorously ventilated day after day, rendering them wholesome and habitable, but from an agricultural viewpoint the slope may cause a climate totally bad, or partially bad, and the mountain farmer must look carefully beyond superficial appearances, and, it must be stated with regret, beyond much of the exploitation literature, for those favorable slopes down which he may induce the dollars to roll into his bank account.
The maximum amount of heat is received by the land from the sun when the sun's rays fall directly upon it—that is, at a right angle to the soil surface-but in our latitude this can occur only where the land slopes several degrees toward the south or toward the sun. A northerly slope, be it ever so slight, is a slightly cooler slope, and this condition includes a multitude of accompanying influences. Evaporation will be considerably less, and dry farming may be more safely practiced, as the moisture can be more easily conserved; on the other hand, since it receives less heat from the sun, the spring season on such a slope will be slighly delayed, crops
will be less precocious, and plant growth, after having started late, will be appreciably slower throughout the summer. This is often manifested by the fact that an alfalfa field on a north slope will yield but three crops safely, while a field on a southerly slope will yield four.
It is almost exactly as if the place were removed a much greater distance from the Equator; though a place nearer the North Pole would really be in the sunshine a greater number of hours per day, for the days are longer in summer with increase in latitude. It is for this reason that the Manitoba, Saskatchewan, and Alberta countries are good grain producers. The sun's rays are seriously slanted and their good effects greatly lessened, yet the days are so much longer that grain can be successfully grown there, whereas it might be a failure in middle latitudes on the same angular slope from the sun because of our shorter days.
LONGITUDINAL COMPARISON OF SLOPE.
Considering the surface slope only, a field slanting 1° to the north lies in the same solar climate as a level field located 70 miles farther north, on account of the curvature of the earth's surface. A field sloping 5° to the north in southern Utah (latitude of southern Missouri), which is not an unusual slope for a farm, is equal to a southern Idaho latitude (latitude of central Iowa). Likewise, a 5° slope to the south in southern Idaho is in the same solar climate as is a level field in the latitude of southern Utah, 350 miles nearer the Equator. It is a fact that the Santa Clara Valley in southern Utah, having a good southerly slope, has a climate, with resultant crop conditions, similar to those of Phoenix and Yuma, Ariz., except that summer maximum temperatures are not so high because of a good air drainage over this region.
ABSORPTION AND RADIATION OF HEAT.
An oval or convex surface of a knoll in an orchard or field receives less heat from the sun than a level tract, thus helping to keep the daytime temperatures lower; and at night a greater loss of heat is experienced than from a level tract, so that its night-time temperatures also often are lower. Therefore the climate of the top of a knoll or a hill is colder than the climate on a level field. Also, a narrow valley, or a small round one, receives more heat in the daytime by the collection of the rays and loses less at night by radiation than does a level tract, and its climate, therefore, is appreciably warmer; it is a great deal warmer than the knoll or ridge, though the valley and the ridge under consideration be in the same general altitude. For this reason many very high round or par
tially inclosed valleys are good crop regions. This temperature difference between hill and hollow, due to differences of radiation, is greatly accentuated by winds and by air drainage.
EVAPORATION OF MOISTURE.
A storage reservoir for irrigation water located in a bowl-like depression in the tops of the mountains will not only contain water that is comparatively warm, but it will suffer a great loss by evaporation, whereas a reservoir located in an east-and-west canyon in the shadow of a south ridge or mountain may lose only a fraction as much water by evaporation as the reservoir exposed in the sun between the sloping hills. Narrow agricultural valleys experience the same sort of effect from the sun, and their crops in springtime are very precocious, often dangerously so, when there is a probability of injury from late spring frosts. The wider valleys show the result of this collection of the sun's heat much less than the smaller, narrower valleys.
The northerly slopes of the mountain, from which the snow and rain are much more slowly evaporated, are where we find the mountain forests, while the southerly slopes, which are quickly dried in the sun after a storm, are usually covered with a ragged blanket of sagebrush, and often carry no vegetation at all.
DANGER OF FROST.
The greatest weather enemy in all fruit districts, east and west, is the late vagrant spring frost which throws itself into the lap of spring without ceremony-the frost that goes sneaking across the country under the immense high air-pressure areas that are occasionally seen on the weather maps, and kills the fruit buds after all nature has apparently concluded that spring has safely arrived.
In the mountainous districts the maximum action of these frostproducing high-pressure areas is considerably hindered, but it is unmitigated in the Plains States and in the East. The dangerous sapstarting warm periods of winter occur in the mountains from the same sort of low barometer areas as in the Mississippi Valley and the East, but the progress of these areas is greatly retarded and their effect minimized by the high mountain peaks and the general elevation of the land. A winter warm spell of sufficient length to start the sap practically never occurs in the mountain valleys, where a more equable condition of the storm-carrying atmosphere is enforced by the impeding mountains, and thus the trees are subjected to less rigorous winter weather and are awakened from their winter dormancy in a perfectly natural manner when spring has duly arrived,