1290 



FROST 



FRUIT-GROWING 



1,500,000 pounds of air 5° F. However, it is seen that 

 1,800,000 B. T. U.'s are just capable of maintaining 

 42,000 pounds of air 5° F. above the surrounding 

 atmosphere when there is no wind-movement. This 

 means that even with large trees having the abiUty of 

 reflecting back a considerable amount of heat, and with 

 the soot and smoke acting more or less as a blanket, the 

 loss by radiation, convection and absorption is enor- 

 mous. As a matter of fact, ft of the heat generated by 

 the orchard-heaters is lost, and the eflSciency is, there- 

 fore, less than 3 per cent. Though effective and well 

 within the financial possibility of application, the 

 orchard-heater is nevertheless a wasteful appUance. 



In the above calculations, the effects of wind-move- 

 ment have not been taken into consideration. Take 

 the case of a pot placed in an outside tree row heating 

 a space 25 feet square and 12 feet high. This space 

 contains in round numbers 600 pounds of air. The 

 standard pot will generate 600 B. T. U.'s a minute, or 

 sufficient heat to raise the temperature of 600 pounds 

 of air about 4° F. This wiU be true if there is no wind- 

 movement and if there is very httle radiation of heat. 

 However, if the air moved only 100 feet a minute, or a 

 little more than 1 mile an hour, the temperature could 

 never rise more than 1° above the temperature of the 

 incoming cold air. At 4 miles an hour it could rise but 

 J|° F. This will be true only in the outside tree rows, 

 on the side from which the air-movement comes. This 

 shows why it is often difficult to protect the outside 

 rows from frost-injurj-. Naturally, with the orchard in 

 the form of a square, all the rows beyond the first, on 

 account of air-movement, would receive a certain 

 amount of heat from the first row. However, with a 

 high wind of 18 to 20 miles an hour and a temperature 

 of 10° F. or more below the danger-point, the problem 

 of frost-prevention becomes a serious one. The num- 

 ber of fuel-pots must be three or four times the number 

 required for ordinary orchard-heating. 



The value of smoke. — The discussion so far has con- 

 sidered mainly the value of fuels from the standpoint 

 of heating. There is some value in the smoke which is 

 generated but very much less than there is in the heat. 

 When it is calm there is httle difficulty in maintaining 

 a heavy smudge with only fifty orchard heaters, or 

 fires, to the acre, but a very hght breeze will quickly 

 drive it away. Experience has shown that the smudge 

 is valuable when the temperature drops somewhat 

 below the danger-point about sunrise. In cases of this 

 kind, the smoke acts as a screen and prevents the too 

 sudden warming up or thawing of the frozen fruit. 

 However, it is unsafe to depend on smudge alone. 



The use of electricity in frost-prevention. — During 

 recent years much thought has been given the matter 

 of frost-prevention by electrical engineers. However, 

 let it be said that some other means than that of direct 

 electrical heating must be employed. If we take the 

 above figures indicating the amount of heat energy 

 which must be expended to the acre to raise the teni- 

 perature 5° F. in an orchard and maintain it above 

 that of the surrounding atmosphere, we find that this 

 is equivalent to appro.ximately 700 H. P. of mechanical 

 energy. In the transmission of electrical energj- from 

 the source of power, there is always a heavy loss, so 

 that fully 1,000 H. P. of mechanical energj' would have 

 to be generated in order to raise the temperature 5° 

 F. in an acre of orchard. From this it will be seen that, 

 although our large electrical power plants are carrying 

 a very hght load during the hours of 1 a.m. to 7 a.m., 

 the amount of reserve power would be so small in 

 comparison with the demands that the largest power 

 plant would cover but a very small area. Of course, 

 this consideration takes into account the conversion 

 of mechanical energy into heat energy. In actual 

 practice, the electrical heater is so inefficient that it is 

 wholly beyond the range of possibihty for orchard- 

 heating. The problem of frost-prevention by electrical 



methods must be attacked from a different side, either 

 by the use of high tension discharges or by the use of 

 large electric fans that will tend to stir the air or pro- 

 duce a chimney effect so as to carry the cold air 

 upward. Even the latter will be useless when very 

 low temperatures are accompanied by high winds. 



A simple method of estimating the quantity of fuel 

 necessary to raise the temperature of the air in an acre 

 of orchard any number of degrees Fahrenheit under 

 every condition is as follows: In a full bearing orchard 

 there are appro.ximately 500,000 cubic feet of air to the 

 acre which must be heated continuously, it being con- 

 sidered that the height to which heat must be added 

 is about 12 feet. By experiment, it has been shown that 

 it will require about 0.75 to 1.00 B. T. U. to the cubic 

 foot an hour to maintain the temperature 1° F. above 

 that of the surrounding atmosphere. Therefore, it 

 will require 375,000 to 500,000 B. T. U.'s an hour, under 

 average conditions to maintain the temperature of an 

 acre of orchard 1° F. above that of the surrounding 

 atmosphere. Since one pound of crude-oil or distillate 

 contains appro.ximately 18,000 B. T. U.'s, the number 

 of pounds of fuel-oil required to the acre-hour will be 

 twenty to twenty-eight pounds. Since a pound of oil 

 is approximatelj' one pint, the quantity of oil an acre- 

 hour for 1° F. rise wiU be two and one-half to three and 

 one-half gallons. As shown above, the ratio of wood, 

 coal and oil is about as 1:2:3, wood having 6,000, coal 

 12,000, and oil 18,000 B. T. U.'s to the pound. 



Bibliography. — Some recent publications on frost 

 protection are: "The Protection of Orchards in the 

 Pacific Northwest from Spring Frosts by Means of 

 Fires and Smudges," P. J. O'Gara, Farmer's Bulletin, 

 No. 401, U. S. Dept. Agric. "The Prevention of Frost 

 Injury in the Orchards of the Rogue River Valley, 

 Oregon," P. J. O'Gara, Bulletin No. 5, Office of the 

 Pathologist and Local United States Weather Bureau 

 Station, Medford, Oregon. "A comparative Test of Fuel 

 Oils and AppUances Used in Orchard-Heating to Prevent 

 Frost Injury," P. J. O'Gara, Bulletin No. 6, Office of the 

 Pathologist and Local United States Weather Bureau 

 Station, Medford, Oregon. "Forecasting Frosts in the 

 North Pacific States," E. A. Beals, Bulletin No. 41, U. 

 S. Weather Bureau. p j O'Gara. 



FRUIT-GROWING comprises all the knowledge 

 and practice that are directly concerned in the produ- 

 cing and handhng of fruits. Pomology (hterally, 

 science of fruits) is sjmonjTnous with fruit-growing. 

 There has been an effort to divorce the terms pomology 

 and fruit-growing, making the former to comprise the 

 scientific and classificatory subjects and the latter the 

 practical subjects; but such division is arbitrary and 

 is opposed to usage. The word "growing" can no longer 

 be held, when used in such connection, to designate 

 merely the planting and care of fruit-plants, for all 

 good practice is necessarily associated with scientific 

 knowledge and theory. Fruit-growing is a more famihar 

 and homely term than the Latin-Greek word pomology, 

 and for that reason it has seemed to some persons to 

 be less adaptable to the formal presentation of the 

 knowledge connected with fruits. It is significant, 

 however, that with the exception of Prince's "Pomo- 

 logical Manual," the fruit books that have done much 

 to mold pubUc opinion in America have not been known 

 as pomologies, notwithstanding the fact that the greater 

 number of them have given great attention to formal 

 descriptions of varieties. The term pomology is founded 

 on the Latin pomum, a word that was used generically 

 for "fruit." In later Latin it came to be associated 

 more particularly with the apple-like fruits. The word 

 is preserved to us in the French pomme, meaning 

 "apple," and in other languages of Latin derivation. 

 In English we know it as pome, a botanical term used to 

 designate fruits that have the pecuUar morphological 

 structure of the apple and pear. This use of the term 



