PRECIPITATION AT HIGH LEVELS-Continued. HOLCOMB CREEK, SAN BERNARDINO COUNTY. [Latitude, 34° 18'; longitude, 116° 58'. Elevation, 5,220 feet.] Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec. Annual. 1893.. 1894. 1895. 1896. 1897. 0.15 1898. 6.37 2.96 4.22 0.70 8.27 0.25 2.44 2.75 14.73 46.43 46.59 2.73 26.43 1.85 0.34 0.74 1.28 0.00 4.10 1.70 10.48 16.88 18.39 0.00 0.40 5.82 1.30 2.25 0.00 0.00 5.00 0.00 0.00 2.85 0.65 0.00 0.25 1.28 1.12 2.01 14.16 1176-Bull. L-03-15 1892. 3.00 1.25 1.25 0.25 0.00 0.00 0.50 0.00 5.00 4.25 24.75 0.50 5.75 0.00 0.00 0.00 1.75 0.00 0.00 0.25 0.00 1893.. 1894. 10.50 10.75 1.25 3.75 2.25 0.00 0.25 1.25 10.00 0.00 0.00 1.00 1.50 1.50 1.00 20.00 6.75 6.75 0.14 0.63 5.00 14.00 1.50 36.50 FROST:" With the possible exception of the loss occasioned by insect pests, there is probably no one cause of loss so seriously affecting crops in California as frost. Notwithstanding statements sometimes published that certain areas are in the so-called frostless belt, there does not appear good reason for believing that any portion of the State may not be visited by frost. The losses to the fruit crop, both citrus and deciduous, through frost have been so large that special attention has been given to methods of protecting orchards, and these methods are discussed in detail in the following pages. With citrus fruits the frosts of December, January, and February are to be guarded against, the fruit being ripe and ready for shipment. With deciduous fruits the late spring frosts do the damage. Almonds, apricots, grapes, peaches, and prunes are hurt while in bud, or while the fruit is just setting, by the frosts of March and April. The damage depends, in all probability, as much upon the condition of the tree as the degree and duration of the cold. For example, a sharp frost during the first or second week of April sometimes does less damage if the trees are fairly past the blossoming period than the same frosts would have caused occurring about the middle of March. Attention is invited to the excellent table prepared by Mr. Samuel H. Gerrish, of Sacramento, giving the dates of first and last light and killing frosts, also the dates of blooming fruit. trees in Sacramento from 1869 to 1901. The protection of gardens, both vegetable and flower, is also important. The particular frosts affecting gardens are the frosts of February, March, and April, and it is pointed out in the succeeding pages that the same general principles used to protect orchards should be followed in the protection of gardens. A clear, still night following thirty-six or forty-eight hours of boisterous north wind is likely to be followed by frost, particularly if the movement of the air in the given locality has been such as to cause a settling of cold, relatively dry air strata in the hollows or depressions of the land. The formation of frost is essentially a problem in air drainage, and if by any means we can prevent streaks, pools, or basins of stagnant, cold, dry air we can largely prevent frost. Frost is the water vapor of the air deposited upon the plant at a temperature below 32° F. The damage to plant life is caused by the falling temperature. The water vapor plays the part of an index only. Indeed, the action of the water vapor is preventive. Dry air at a temperature of 32° F. weighs 563 grains per cubic foot. Vapor of water at 32° F. weighs 2.1 grains per cubic foot at a saturation of 100 per cent. Air at a temperature of 25° F. weighs 572 grains per cubic foot. Given a little time, therefore, on a still, clear night the loss of heat by radiation from the plant surfaces and the ground will bring about a settling of the colder air to the bottom. The ground will be covered with frost, while thermometers 6 feet above the ground will record 34° or 35° F. Vegetables and flowers, therefore, unless grown upon sloping or terraced ground, are at a decided disadvantage compared with tree fruit in the matter of frosts. NATURE OF FROST. It can not be emphasized too clearly that it is the low temperature and not the solidification of the water which does the damage. If there be but little vapor in the air there will be but a light frost apparent, and yet the temperature may be so low as to cause great injury. The so-called hard, dry frost, also called black frost, does, as is well known, even more injury than a Since this article was written a number of orchard-heating devices have been patented by various frost prevention companies in California. Oil fire pots have been tested and it is claimed given very satisfactory results. Gravity oil distillate is used as fuel and about eighty oil pots to the acre will insure protection. heavy frosts. Water vapor at 25° F. completely saturated weighs 1.6 grains per cubic foot. In the fall from 32° to 25° nearly half a grain per cubic foot, if the saturation were 100 per cent, would be condensed, appearing in visible form as a frost flake. A certain amount of heat was given off in the transformation of this invisible water vapor into ice, and an exactly equal amount of heat (known as the latent heat of vaporization) will be in turn required to change this frost flake back into vapor. We give special attention to this point because it would appear theoretically that the secret of successful protection of garden truck and delicate flowers will be found in this action of water, both in setting free heat at the time when the temperature is falling, and on the other hand in using up heat and thus acting as a retard or brake when the temperature begins to rise quickly. It is now quite generally believed that as much injury results from the sudden warming up of the dormant and thoroughly chilled flower or vegetable as from the chilling itself. In the work of protecting fruits from frost it has been found very necessary to interpose some screen early in the morning between the sun's rays and the frosted fruit. With flowers and garden truck this can be much more easily accomplished than with fruit. In this respect the gardener has a decided advantage over the orchardist. The following is an excellent statement of how the plant is injured: HOW FROST INJURES PLANTS. Low temperature congeals the watery part of the cell sap and also the intercellular water content of the plant. Within certain limits this is not or may not be injurious, providing the protoplastic contents of the cell are able to absorb the water and do this before the cell structure collapses as a result of insufficient cell turgor. Frequently the frosting of plants is followed by a sudden rising of temperature, in which case much of the water which was part of the cell sap in the normal condition of the plant escapes through the cell wall into intercellular spaces, or even from the plant entirely, and thus, the protoplasm of the cell being unable to assume its normal condition, becomes disorganized and decomposition follows. (Prof. E. R. Lake in the Oregon climate and crop bulletin, July, 1900.) PROTECTION OF ORCHARDS FROM FROST. During the past five years the Weather Bureau office at San Francisco has been called upon to give particular attention to the problem of lessening the injury to fruits by frost. By direction of the Chief of the Weather Bureau, during the year 1900 the forecast official for the southern half of the Pacific slope made an extensive journey through California with the special purpose of studying the methods of protecting deciduous fruits from frost. This journey was the natural outgrowth of the excellent work inaugurated by Mr. W. H. Hammon, formerly professor in the Weather Bureau, while in charge of the San Francisco office. During the years 1897, 1898, and 1899 the unusually dry winter conditions, with frequent and prolonged frosts and lower temperatures than had been previously reported in many of the chief fruit-growing centers of southern California, made it imperative that some steps should be taken to minimize the injury to citrus fruits by frost. The problem as presented to the forecast official was of a twofold nature: First, a study of the conditions preceding frost, so that he might with reasonable certainty give timely warning to the fruit growers; second, a study of the methods, means, and devices for protecting fruit from injury by low temperatures. The first has been solved with a fair measure of success. In the second problem the Weather Bureau had the valuable assistance of certain practical fruit growers, who willingly and readily tested the various devices proposed for smudging and cheerfully gave this office the benefit of the many practical experiments made by them in smudging, irrigating, heating, and covering. A bulletin on frost fighting, by Alexander G. McAdie (Bulletin No. 29), was issued on March 13, 1900, and nearly 3,000 copies distributed to those most interested in fruit growing. A previous bulletin (No. 23) upon frost, when to expect it and how to lessen the injury therefrom, by Prof. W. H. Hammon, had been issued on November 10, 1898, while a Farmers' Bulletin, No. 104, by Prof. E. B. Garriott, Notes on Frost, was issued June 15, 1899, which treated of frost protection in general. It has become evident in California that the fruit grower must possess a degree of intelligence certainly as high as is demanded in any one of the usual vocations of life. The successful orchardist must be a skilled farmer and a good business man and, at the same time, be familiar with the chief principles of modern science. He must be chemist, entomologist, and physicist, as well as fruit grower. In the matter of protecting his crops from frost, for example, he must know exactly what method is best suited for his crop, for the locality, and for the season, and be prepared to act promptly, or else the greater portion of the year's profits will vanish in the course of a few hours. In what follows extensive use will be made of Bulletin No. 29, since experience has shown that the principles of frost fighting laid down therein are essentially correct. While this bulletin was written chiefly with a view of protecting the citrus fruit crops of California, particularly of the section south of the Tehachapi, from frost, the principles hold, as a general rule, for the protection of deciduous fruits also. In October and November, 1900, an attempt was made to extend the benefits of the Weather Bureau work in connection with frost to the fruit growers of central and northern California, particularly to the growers of almonds, apricots, peaches, prunes, pears, apples, grapes, and figs. Many fruit ranches were visited, and the details of losses by frost gathered from ranch superintendents and others, together with all data available relative to the exposure of the fruit, the lay of the land, and the lowest temperatures. The following facts stand out prominently from the general mass of statements. First, that in California the greatest injury is done deciduous fruits by the late spring frosts occurring as late as the 23d of May, when fruit is well formed, frequently resulting in the loss of three-fourths of the crop in the case of the more tender fruits, as for example, almonds and apricots. Second, in all the fruit ranches visited rough maps of the localities showed conclusively that the frost occurred chiefly in the low places, basins, and bottoms, or where the cold air had drained down and settled. The principle laid down in Bulletin No. 29, that frost was primarily a problem in air drainage, was conclusively upheld. Wherever the air was stagnant the injury from frost was most marked; and, conversely, wherever the air was in motion there was little damage from frost. Fruit on open benches, hillsides, and terraces escaped. The streakiness of frost and the many apparent irregularities in its formation can be explained easily if we remember that there are currents and stream lines in the air, and that these currents may have rather sharply defined limits. A slow-moving current of air on a still night in an orchard that appears to be nearly level may result in an absence of frost along its path, while close by, where the air is stagnant, frost will be formed. A third particular point resulting from this visit to the ranches was the confirmation of the belief that the damage from frost could be greatly lessened if some means were provided whereby the chilled fruit could be protected from the sudden warming at sunrise. Some rough temperature observations made in ranches at about the time of sunrise on frosty mornings showed a rise of as much as 10° in the air temperature within thirty minutes. It was also noted in several ranches that the areas of greatest loss by frost were those where the sun's heat came suddenly upon the trees. It is believed that much fruit can be saved even when chilled or frozen if some screen is interposed between the fruit and the sun, so that the warming may be gradual. It is even admissible to thoroughly wet the fruit with cold water, and there are numerous instances of fruit escaping serious injury even when it has been covered with a thin coating of ice. It is of the utmost importance that the thaw for an hour or two following sunrise be gradual. The following methods of protecting fruit from frost are taken from Bulletin No. 29: METHODS OF PROTECTING. Every fruit grower should put himself in communication with the nearest center of distribution of weather forecasts. If possible he should be in daily communication with some Weather Bureau office. Whenever frost warnings are issued for his locality he should carefully determine the temperature and dew-point, as elsewhere described, frequently during the late afternoon and night. A good outfit consists of a metallic thermometer so arranged as to automatically close an electric circuit and ring an alarm whenever the temperature of the air reaches 32°. In addition to a reliable sling psychrometer there should be some small device for testing the motion of the gentle air currents in the orchard. Too much attention can not be given to this question of air motion. Many smudging devices have failed to be effective because of a slow movement of the smoke away from the orchard. |