THE DEVELOPMENT OF ENGINEERING METHODS FOR THE TREATMENT OF LOOSE SMUT IN WHEAT Thesis fer Ike Degree of M. S. MICHIGAN STATE (301.2153? Rob-art ‘v‘v’iIIiam K5955 1951-. ' nut-1519 \4 -—_-— - n This is to certify that the , thesis entitled ..._ Ti—O o "The Deve10pment of Engineering Methods for the Control of Loose Smut in Wheat" presented by I , Robert W. Kleie ' \ _. has been accepted towards fulfillment L ' of the requirements for n.3, degree in Agricultural I . Engineering I ' ._ :3 Major prof ssor I; : mgcégust 1'7. 195; fi. " I I- 0-169 " n I -l - *. C Q l THE DEVELOPMENT OF ENGINEERING METHODS FOR THE TREATMENT OF LOOSE SMUT IN'WHEAT by Robert William Kle s A Thesis Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science In partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering 1951 THFQ;Q ACKNOWLEDGMENTS The author wishes to express sincere appreciation and gratitude to the following: \ Doctor E. H. Lucas for his sincere advice and help- fulness in carrying out this work. Doctor W. M. Carleton for his guidance and many helpful suggestions. I Professor D. E. Wiant for his aid and advice during the early stages of the project. Professor H. M. Brown for his aid and helpfulness in providing materials and plots for field tests. Doctor D. J. de Zeeuw for his aid in the determina- tion and analysis of field tests results. Professor I. B. Baccus for making equipment and facilities of the Electrical Engineering Department available for use in this work. 258353 ii TABLE OF CONTENTS Page INTRODUCTION --------------------------------------- 1 REVIEW OF LITERATURE ------------------------------- 3 Loose Smut ------------------------------------ 3 Present Methods for Treatment of Wheat for Loose Smut ................................ 5 Other Methods of Controlling Loose Smut ------- ll Treatment by Infrared Radiation --------------- 12 Dielectric Beating as a Method of Treatment --- 2O TESTS OF TREATMENT WITH INFRARED RADIATION --------- 31 Objectives .................................... 31 Apparatus and Equipment ....................... 32 Test Procedure -------------------------------- 34 Tests Conducted ------------------------------- 55 TESTS OF TREATMENT BY'DIELECTRIC HEATING ----------- 56 Objectives ------------------------------------ 55 Determination of Electrical Preperties of Wheat 57 Calculation of Power Requirements ------------- 65 Apparatus and Equipment ----------------------- 57 Test Procedure ................................ 72 Tests Conducted - .............................. 75 SUMMARY AND CONCLUSIONS ............................ 86 LIST OF REFERENCES --------------------------------- 89 Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 10 11 12 13 14 iii LIST OF FIGURES Wheat heads showing appearance and development of loose smut ................ The major components of a wheat kernel --- Electromagnetic Spectrum showing the infrared region -------------------------- Wave length distribution of 250 watt heat lamp ................................ Radiant energy distribution of one and two 250 watt lamps ....................... Simple schematic diagram showing principles of dielectric heating .................... Equivalent parallel circuit of a capacitor and its vector relations Apparatus used for radiant heating tests - A kernel of wheat was placed over a butt- welded thermocouple. Extra kernels were strung on the wire to shield it from . direct light. ---------------------------- Radiant heating apparatus and measuring instruments ------------------------------ Time-temperature curves as affected by color of wheat and height of lamp -------- Effect of temperature on germination of Yorkwin wheat ............................ Effect of moisture content on germination after heating ............................ Effect of temperature on germination, emergence and smut control of American Banner wheat -—-‘-------‘-----‘---‘--~---- Page 14 18 18 21 26 33 35 37 39 4O 44 49 Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 15 16 17 18 19 2O 21 22 23 24 25 26 27 28 iv Effect of temperature on germination, emergence and smut control of Goens wheat Test capacitor used for determining dielectric characteristics of wheat ------ Boonton type 160-A Q-meter used for determining dielectric characteristics of wheat Diagram of the Q-meter circuit ----------- Effect of moisture content on the dielec- tric prOperties of Vigo wheat as determined by Q-meter .................... Wheat was placed in and contained by a cardboard ring ........................... Close-up view of plates with sample in place .................................... Dielectric heating apparatus and measuring instruments - .......... -- ....... Sample of wheat being prepared for treatment Schematic diagram of grounded grid Hartley oscillator circuit for dielectric heating ---------------------------------- Effect of treatment temperature on germination of Yorkwin wheat ............. Cooling rate curves of two samples after potentiometer indicated 86 degrees at time of cut-off Relationship between heating time and SO-second temperature for Illinois number 1-128 wheat Effect of temperature on Illinois number 1-128 spring wheat with dielectric heating --- ............................... .--‘--------‘----“-‘-‘-----““- Page 52 58 60 62 65 68 68 70 7O 71 75 76 78 83 Table Table Table Table Table Table Table II III IV VI VII LIST OF TABLES Effect of Temperature on Germination ..... Field Test Data of American Banner Wheat Treated with Radiant Heat ---------------- Field Test Data of Goens Winter Wheat Treated with Radiant Heat ------ f --------- Summary of Field Test Data (American Banner) .................................. Summary of Field Test Data (Goens) ------- Relationship Between Moisture Content and Dielectric Constant .................. Field Test Data on Treatment of Illinois Number 1-128 Spring Wheat by Dielectric Heating ---------------------------------- Page 42 47 50 55 53 64 80 INTRODUCTION Loose smut, while not as serious as many other diseases of wheat, does cause the loss of a considerable amount of wheat each year. Even with limited infections the aggregate loss in the entire wheat crop is enormous. It is estimated that the average annual loss of wheat due to loose smut is ten million bushels. The significance of loose smut as a factor affecting the economy of wheat production should not be minimized. The damage done by loose smut is not nearly as obvious as that done by many other diseases. While the infected wheat is growing in the field it appears very normal and the smut fungus can not be detected. Likewise, after wheat is harvested, there is no method of distinguishing infected seed from.normal seed. It is only for a short period, during the flowering stage of the wheat, that the presence of loose smut can be observed. During this brief period the infected heads appear as black masses of smut spores, instead of normal wheat heads. Such infected heads have been known to constitute as much as 40 percent of the total number of heads, and although this is an extreme example, it is obvious that even a con- siderably lesser degree of infection could have a very significant effect on yield. The treatment of seed wheat for loose smut is not being practiced extensively, and there are several apparent reasons why this is true. One reason is that there are other diseases which are more serious in some areas, and it is natural to be concerned with the greatest menace. Secondly, the harmful effect of loose smut is less obvious and more difficult to appreciate than many other diseases. The third, and probably the most important reason, is that the only proven method of treating wheat for loose smut is extremely tedious, laborsome, nmssy, and difficult to perform. This water bath method is effective, but the temperature involved is extremely critical and difficult to control. Failure to control this treatment closely enough can result in more damage than smut infection. Because of the need for some effective, practical, and convenient treatment for loose smut, the research work reported in this thesis was conducted. The sole purpose of this project was to develop an improved method for treating seed wheat for loose smut. REVIEW OF LITERATURE Loose Smut (Ustilago Tritici) Loose smut of wheat, commonly called "smut" or "black- head" is different from stinking smut (bunt) and flag smut, the other smuts of wheat, in that its presence becomes obvious just as soon as the wheat heads out. The diseased heads are usually completely destroyed, but occasionally a head may be only partially destroyed. Dark brown or black masses of smut spores, or "seeds" of the smut fungus (Figure 1), appear along the central stalks of the heads, instead of the normal chaff and blossoms. The smutted heads emerge from.the boot slightly earlier than the normal heads, and the smut spores are enclosed in a fragile membrane which soon ruptures, releasing them. The Spores are easily shaken from the infected head and may be carried a considerable distance by the wind and insects. The diseased heads are most conspicuous during this period of spore distribution as they are erect and usually slightly above the normal heads. The spore mass is spread over the field about the time the wheat is in bloom. Some of the spores lodge between the glumes or chaff of the normal wheat heads, where they germinate and grow within the very young wheat kernel. The smut fungus develops as the kernel develops and becomes dormant as the wheat matures. These kernels are then smut infected, but because the smut fungus lies dormant it is impossible to distinguish between them and healthy kernels. The smut fungus resumes its growth and development when the infected kernels germinate and start to grow. The smut deve10ps as the wheat plant grows and makes its appearance at the time of heading by replacing the blossom with a mass of spores. An appreciable amount of smut infection can be expected in a wheat crOp when the seed is obtained from a field showing smut, unless the seed is properly treated before planting. Each infected seed develops several heads, all of which are usually infected, so there are usually several smutted heads in a group. The losses caused by loose smut are a direct reduction in the yield due to a reduction in the number of normal heads. The number of heads which are smutted is usually less than 5 percent, but may be as much as 40 percent in extreme cases. In addition, it has been found that plants infected with loose smut winter-kill much.more easily than uninfected plants. This situation is, of course, desirable from the standpoint of controlling the smut and decreasing the percentage of diseased heads. On the other hand, the infected seeds which are winter-killed must be considered as a loss of normal yield, unless the amount of seed planted is increased to counteract this loss. Figure 1. Wheat heads showing appearance and development of loose smut. A. B. C. D. E. F. Normal head. Smutted head in the boot. Smutted head as it emerges. Stage of spore distribution. Rachis after spores are gone. Partially normal and partially infected head. When a smut infected field of wheat is harvested, there is no evidence of the smut except the naked stem or rachis. There is nothing remaining to discolor, damage, or lower the wheat quality in any way except for seed wheat. Loose smut has no harmful effect on feeding quality or milling quality of wheat. (5) Loose smut occurs in all parts of the United States where wheat is grown. It is rather rare, however, in the arid western states and more prevalent and destructive in the more humid areas of the Midwest and East. The amount of moisture present during the flowering stage has a very significant effect on the degree of infection of the resulting wheat. In areas where it is extremely dry during this stage, loose smut is no problem. Present Methods for Treatment of Wheat for Loose Smut The use of contact fungicides, such as formaldehyde or copper sulfate, are not effective in controlling loose smut because they act only upon the surface. The smut fungus which is carried inside the wheat kernel can only be killed by a treatment which.will penetrate the wheat kernel without dam- aging it. Heat is known to be effective in killing the smut, but the wheat germ can also be killed by heat at only a slightly higher temperature than the smut. For this reason, any heat treatment must be controlled accurately. In the past, a hot water bath.has been used for applying heat to infected seed wheat. E35; IL :93:- 2 V Figure 2. The main components of a wheat kernel. 1. Bran or outer coat. 2.* Endosperm or starch. 3. Germ or living part. * It is believed that the smut mycelium lies dormant in the endosperm. Modified 15233 bgth method. Following is an outline of a procedure for treating seed wheat for loose smut. (5) This method is known as the modified hot water bath.method. 1. Soak wheat four to six hours in cold to luke- warm water. 2. Dip wheat in water at 49 degrees Centigrade for one minute. 5. Soak wheat for ten minutes in water at 54 degrees Centigrade. 4. Dip for one minute in cold water. 5. Spread wheat on canvas floor, not more than two inches thick, for drying. The equipment and materials needed for this treatment would'be: l. A source of live steam 2. Three barrels or similar containers 5. ‘Water 4. Floating thermometer 55 degrees Centigrade 5. Gunny sacks or screen baskets 6. Canvas covering for floor. Single 3.3.3122 Rajah method. Another hot water treatment Whic111makes use of only one soaking period is performed as follows: 1. Full sacks only half full of wheat and tie tightly at the top. This is to allow for swelling. 2. Soak wheat for one hour and thirty-five minutes in water at 49 degrees Centigrade or one hour and fifty minutes in water at 48 degrees Centigrade. 3. Spread wheat in a two inch layer on a canvas floor, for drying. The equipment for this treatment would be the same as listed for the modified water bath.method. The single bath treatment takes much longer, however, so for a given capacity, larger facilities would be required than for the modified method. Stggm.bggh:method. Experimental work has been performed, using live steam for treating seed wheat. Tapke (21) reports the following procedure used in experimental investigations conducted in the early 1920's. 1. ‘Wheat was soaked for four hours in cold water. 2. Wheat was then placed in a small forced air drier equipped to circulate a saturated atmosphere of ‘ constant temperature. 3. Saturated air with a temperature between 26 de- grees and 48 degrees Centigrade was obtained by using steam and was circulated through the seed wheat for periods of one to five hours. 4. The wheat was then dried by forcing air through it. Although this treatment was very effective and resulted in less injury to germination, the equipment required and 10 the problems of application were such.that it was considered extremely impractical. Limitations 23 known methods 23 treatment. Because of the difficulty of maintaining a constant temperature of a water bath over long periods of time, these methods have not been recommended for use by individual growers. They have never been recommended for treatment of sufficient quantities to plant an entire crop, because of the time and labor involved. Where these methods have been practiced it has usually been on a community basis where an elevator or a creamery has made facilities available. There is normally a loss of germination in seed which has been treated. Cracked, scratched, or broken grain is almost certain to be killed in the treatment process. This factor is considered by some to be desirable in that it destroys those seeds which may be weak and slow to develop. In mechanically harvested grain, however, the percentage of kernels which are scratched or cracked may be quite high and the germination greatly reduced by treatment for loose smut. It is recommended that germination tests be run on treated seed before planting and that allowance be made in the rate of seeding to counteract the loss. Previous experimental work has also indicated that the injurious effects of hot water treatments are not confined to germination but may extend into the later stages of plant growth. United States Department of Agriculture tests, 11 conducted by Tapke (21) in 1925 showed less yield from.treated plants than from an equal number of untreated plants. There was, however, no appreciable difference in the quality of ' wheat from treated and untreated plots. These results nulli- fied the belief that there might be a stimulation of germination and yield caused by the water bath treatment. The handling and drying of the grain after any of the wet treatments is a problem. The wheat must be dry at time of planting to facilitate feeding in conventional drills. Drying is quite easily accomplished for small quantities, but for larger amounts it becomes an engineering problem. Other Methods of Controlling Loose Smut Control _c_>_f_ 13333 _s__m_l_.l_§ by §_r_y 2}}: conditions. Studies by Tapke (23) at the Idaho Experiment Station have shown that loose smut is controlled by nature in arid areas. Because of lack of moisture at the time of blossoming, the smut spores are unable to germinate in the normal heads. As a result the wheat kernels do not become infected. This relationship to moisture in the air accounts for the prevalence of loose smut in the humid regions and for its rare occurrence in the dry areas of the West. In cases where the same varieties are grown in humid and arid regions, disease-free seed can be obtained for use where loose smut is a problem. This situation is not common, however, 12 as the use of different varieties is usually desirable for areas with such different growing conditions. Smgt resistant varieties.v Various studies have been made to determine which varieties of wheat possess a natural resistance to loose smut. Tapke (22) reports that the Virginia and New Yerk Experiment Stations conducted extensive studies of all common varieties of wheat, between 1922 and 1952. The commonly grown varieties which.were found to be highly resistant were Faltz, Fulcaster, and Dawson. None of these varieties are common in Michigan; however, Berkley Rock, which is commonly grown in this state, has also shown rela- tively high resistance to loose smut. There are, as indicated above, resistant varieties which can be used. On the other hand, there are other characteri- stics which often make these varieties undesirable or less adaptable to local growing conditions than less resistant wheat varieties. Treatment by Infrared Radiation Previously used methods of treatment are effective but have many disadvantages, most of which can be attributed to the fact that the seed has to be wetted. Efforts to find a new method of treatment, therefore, are directed toward determining some method of applying heat without moisture. Previous experience has also shown that where heat is applied, 15 it must be controlled very closely and must create a relatively uniform temperature. These factors indicate that radiant heat mdght be effective in killing the dormant smut mycelium. Frequency and wave length. Radiant heat is infrared radiation which is one form of electromagnetic radiation. Infrared radiation is a relatively wide band in the electro- magnetic spectrum (Figure 3), having a wave length range of from 7,600 to 1,000,000 Angstrom units. This range falls between visible radiation and the longer radar, radio, and television waves in the spectrum. The frequency of electro- magnetic waves is inversely proportional to the wave length. The product of frequency and wave length is a constant and is equal to 186,000 miles per second, or the speed of light. Infrared waves of different lengths have widely varied characteristics. The degree of penetration of various materials is especially important in most applications and varies considerably with the length of wave. In general, the shorter waves of the region near visible light have greater penetrating ability. Reflection and absorption by various surfaces are also important and dependent upon wave length. The heat radiated from an incandescent lamp bulb is an example of the shorter wave length of infrared radiation. A Nichrome resistance heating element, on the other hand, 14 acawca ceasawna wanton» asepoedm caposwdaoauooam .n oaswam k \..\..\ 0.\> Lnua .NJQ. n“: \\ N .t \ ~ 4L.x~n.£t_ A. ..\.Num\ N:t..;.\-...\.wlm\nN l5...\.\\\u vl-x. WQ\IX h...\.....:.~.ur\\v U\. .WUU 5 I C / 3 T I--- z-- - .I-...----ILI-i-. ...... - .- I I I (x e-i -, McGee \\ recs CCCV LO\ 0.x ‘0. .bukkanT HkxfiCO \COU. radiates a medium wave length, while the waves radiated by a steam radiator are longer. Effect 33 surface characteristics 23 absorption and reflection. When radiant energy falls upon a body, part or all of it may be absorbed, part or all of it may be reflected, and part or all of it may be transmitted through the body. Most solids are Opaque to nearly all thermal radiation, which means that no infrared radiation passes through them. Wheat would be classed as opaque, which means that all thermal radiation falling upon it is either absorbed or reflected. For an opaque body, then, the energy reflected plus the energy absorbed is equal to the total incident radiation. or "’ Q4 : QT 11' r: 2r. - 9.9. or or "d “I 3 01' then f+a=l where a.=absorptivity factor or the fraction of the incident radiation absorbed, and r = reflectivity factor or the fraction of the incident radiation reflected. The factors, a and r, then, are inversely related and their values for an Opaque body depend upon the characteristics of the surface. Such things as color, luster, smoothness, temperature, and chemical composition all affect the amount 16 of radiation absorbed and reflected. In general, polished, light colored, or glossy surfaces have lower absorption factors than similar surfaces which are rough, dark, or dull. The values of a and r also vary with the length of electromagnetic waves. Many materials are transparent to certain wave lengths of thermal radiation and almost entirely opaque to others. For a body of this type the wave length 'which is most readily absorbed is affected by the temperature of the body. As an object is heated by radiant energy, the amount and wave length of energy absorbed.will change as the temperature increases. A body which has a constant absorption factor for all 'wave lengths and temperatures is called a "gray body." Often bodies which are not gray bodies are considered such for purposes of calculation. It is conventional, however, to use the mean absorption factor for the temperature range involved, for other than gray bodies. The theoretical object which-would absorb all incident radiation is called a "black body." While many materials are :nearly black bodies and have an absorption factor of nearly one, there are actually no perfect black bodies. The absorp- tion factor, a, is then, the ratio of the radiation absorbed 'by a body to that which would be absorbed-by a black body. Generators 2; thermal radiation. All materials with a temperature above absolute zero radiate energy in the infrared Iregion. The effectiveness and efficiency of radiating objects 17 is greater at higher temperatures and shorter wave lengths. The wave lengths radiated by filament type lamps are very short and near the visible light band. Such generators are highly efficient and convenient for a variety of applications. Most filament type "heat lamps" are gas filled and have tungsten filaments. Common types Operate on 120 volt alter- nating current and are available in sizes of 125, 250, 375, and 500 watts. They are available with various bases and with plain glass or reflector type bulbs. The Operating temperature of tungsten filament in an infrared lamp is approximately 4,000 degrees Fahrenheit, and the wave length of the greatest amount of energy (Figure 4) is about 12,000 Angstrom units. The application 23 radiant heat for treating wheat. Some preliminary investigations have been conducted by Lucas (9) on the use of radiant heat for the control of loose smut. The results of these tests indicate that such a treatment can be effective, but there is a problem-in the design of an apparatus for its application and control. An R-40, 250 watt industrial type heat lamp was used in these studies and the wheat was spread in a single layer directly beneath the central axis of the lamp. This method is satis- factory only for treating very small amounts of wheat because the intensity of radiant energy decreases quite rapidly as the distance from the central axis is increased (Figure 5). 9 If several lamps are used to treat a larger amount of wheat, 18 /',' " ‘ ///x \- \ ,0 \ \ L P v] \\ \ \ \ , - \ Lu Y I' \R \\ 's. - p \ .- \- I \\ x“ I) \\ I. f b I -. / U. 2» I '1” wk] Inrr lffd 4 z 1 A 4 L A; A. _ 4'. J J 1 C 2 4 6 c: L' A. /J /» I5 ;: 21 my ;e we» a /:n 7; f: A ,, y N flrrzx - The exam? I 1 Figure 4. Wave length distribution of an R-40, 250 watt infrared lamp r * '\ I) ”‘1‘“ “1""‘Y v4.27? 0' r fat/ape [flCO -.=, ' \l‘ (2‘ ‘xenigg____ I -1- -_.__J.._-._- 1..- -_ L _._. L- _ -_--) __. -_..i -_. _ t _-__._.L___---_4I 0 4} 8 I2 /6 .80 4,4 o 3.2 Sc: ’76- JhC/.C.S‘ from flr/j‘ cf Lam’s Figure 5. Radiant energy distribution of one ’ and two 250 watt lamps, 56 inches high 19 they can be arranged so that the energy level is relatively uniform. This is accomplished when the lamps are about the same distance apart as they are above the plane of the surface to be heated. Some of the variable properties of wheat which would probably have an effect on its treatment by radiant heat would be: a. color b. moisture content c. size and uniformity of kernels d. chemical composition e. condition of surface f. shape of kernels. These properties which are constant for any one batch of wheat would not be likely to hinder the effectiveness of a treatment. It would be more difficult, however, to make adjustments for prOperties which vary within a single sample of wheat. Variations in size of kernels within a sample, especially, could conceivably cause nonuniform heating and either ineffective smut control or damage to germination. The seriousness of this effect would be determined by the temperature margin between the critical temperatures of the smut mycelium.and the wheat germ. It is hoped and believed that this margin will be greater in the dry application of heat than with the water bath.methods. If such is the case, the influence of the variables involved may fall within the effective but safe temperature range. 20 Dielectric Heating as a Method of Treatment Another method of applying heat without wetting the wheat, would be dielectric heating. This method makes use of a high frequency electrostatic field which is applied to the dielec- tric material to be heated. It is used extensively in industry for heating plywood, ceramics, plastic, and other similar non- conducting materials. Frequencies of two to thirty megacycles are commonly employed for this type of heating. The material to be heated forms the dielectric between the plates of a capacitor, and the radio frequency voltage is applied across the plates. If the plates are large enough and properly designed, and if the dielectric material is homogeneous, the heating is very uniform throughout the material. Because the heat is generated internally and does not have to flow from the surface to the center, much more rapid heating is possible. Furthermore, it is not necessary to overheat the outer surfaces in order to provide for heat conduction inward. The unit used for dielectric heating consists (Figure 6) essentially of a radio frequency generator and a capacitor containing the material to be heated. 93233.9; heating. Whether a material is a conductor or a dielectric (nonconductor) is a relative matter and is deter- mined by the number of free electrons it possesses. A good conductor has a large number of free electrons, while a good dielectric has very few. All materials may be classed as one f/(Cf/‘C/S /'<'1’7/Lj / c \\ AF. / I y 5 "rarer [ Figure 6. Simple schematic diagram showing the principles of dielectric heating 22 or the other or may fall somewhere in between. A good conductor, then, may also be classed as an extremely poor dielectric. The National Electric Manufacturers Association explains the heating of an insulating material as being "due to its own dielectric losses when it is placed in a varying electro~ static field." The application of an electrostatic field to a dielectric material has at least two, and possibly three, effects. First of all, if the material is not a particularly good insulator, there will be some conduction of current through it from one plate to the other. If this takes place there will be some resistance heating. This heat energy would be equal to 12R. In most dielectric materials, however, this is insignificant compared to the other two effects. A second effect of an electrostatic field applied to a material is a distortion of the molecules. The orbits of the electrons are displaced in the direction of the positive plate with respect to the nucleus of the atoms. The nucleus is displaced to a smaller extent toward the negatively charged plate. This effect is called dielectric polarization. There may also be found some displacement of the atoms within the molecules. When these displacements are reversed several million times a second, there is caused an internal atomic disturbance which requires a certain amount of work energy, which is in turn dissipated in the form of heat. 23 Heat is also generated by the rotation of molecules as they orient themselves with the electrostatic field. Many molecules are dipolar, which indicates that they have different centers of positive and negative charge. Because of this, they possess what is called a dipole moment and, when placed within an electrostatic field, attempt to align themselves with that field. As they rotate to come into alignment these molecules, of course, may collide with other molecules and the resulting interactions impart kinetic energy to the thermal motion of the molecules and cause a temperature rise. Any one or a combination of these three effects can cause heating of a dielectric material. Dielectric properties. The amount of polarization, or distortion and rotation of molecules, which Occurs when a dielectric is placed in an electrostatic field, determines the capacitance of the capacitor thus formed. The greater the polarization, the greater is the capacitance. The ratio of the capacitance of a capacitor, having any substance as a dielectric, to the capacitance of a capacitor with a vacuum as a dielectric, is called the dielectric constant. The dielectric constant for a vacuum.then is one and of air 1.000590. For all practical purposes the dielectric constant of air may be considered as one. The dielectric constants of many materials vary with frequency. At extremely high frequencies the field may alternate so fast that there is not time enough for complete 24 polarization to take place. The electronic, atomic, and molecular types of polarization are the most important and the speed with which they can take place depends upon their mass and certain other factors. In most materials the dielec- tric constant decreases as the frequency is increased and, in general, the total dielectric losses and heating effect increases as frequency is increased. Temperature also affects the dielectric constant of many materials. In general, an increase of temperature will lower. the dielectric constant. This is true of all materials which are dipolar, according to Atwood (1), because a rise in tempera- ture and its accompanying increase in thermal action greatly decreases the amount of molecular polarization. The dielectric constant of organic materials is also affected by their moisture content. The dielectric constant .of water is near 81. Therefore, for materials which are nominally insulators, the greater their moisture content, the higher is their dielectric constant. The 22325 factor of a dielectric material in a capacitor is also important in dielectric heating calculations. It indicates what part of the input volt-amperes is dissipated in the form of heat. It may also be defined as the cosine of the phase angle between the applied voltage and the current. This may be illustrated (Figure 7) by either an equivalent series circuit or an equivalent parallel circuit and their vector diagrams. (C) {)1 Another factor sometimes used in work with capacitors and coils is the quality factor or 3. This factor is defined as the ratio of the energy stored in a capacitor to the energy dissipated. In most practical applications Q may be considered equal to the reciprocal of the power factor. The product of the dielectric constant and the power factor is used in dielectric heating calculations and is referred to as the loss factor. Basic formulas and principles. The power required for heating a dielectric material may be calculated as follows: P: [flex/0-4146 (fi‘n) (l) where P = Kilowatts M: pounds per minute C specific heat of material (T,-T5) ::temperature rise in degrees Fahrenheit. This formula gives the power required to raise a given amount of a certain material (work) a certain number of degrees per minute. {._.__4__ PO 0) Figure 7a. Equivalent series circuit of a capacitor and its vector relations m . I i___- PU ._.— : C (4/ Co / . ¢ / 1 NW ‘ i -_ _ -_. RP ._.—J. L..— -____- ;- _-_k?_l_-.~_>—— E ‘+ ' To C’s Figure 7b. Equivalent parallel circuit of a capacitor and its vector relations at = 2 at frequency 0-: phase angle 0 = loss angle cos 9 a power factor = sin ¢ The basic dielectric heating formula, according to Westinghouse (25), is: w s 1.4 a 10'” E ‘fe"§. in which '.'= watts required Ezvoltage across work A=area of work in square inches d = thickness of work in inches fzfrequency in cycles per second !I— e -loss factor or power factor x dielectric constant since E : E,d, where Er: voltage gradient in volts per inch then w: 1.4 s 10‘“ a,‘ re" Ad or AL .-_ [.4 : 10"”5,‘ re" Ad w W = —— if I Ad then W, = [.4 1/0'“ Effe” Solved for voltage gradient L" ( = 2) 5’ Mix/0'“ fe” The current through the work may be determined by the following formula: I =M./o"‘£, flag. (a) where e :dielectric constant 28 Application 22 dielectric heating Egpghggt. One of the advantages of dielectric heating is that for most materials there is a wide range of frequencies that can be used. This makes standardization of equipment possible, as well as the use of fixed frequency generators. This would be important if this method were used for wheat treatment, as the number of treating units used would be limited and, therefore, the cost would be high if special equipment were required. The fact that with dielectric heating the material is heated internally and uniformly is also an advantage where temperature must be controlled very closely. It is believed, however, that the heating in wheat may not be uniform because it is not homogeneous and is, of course, granular with air cells between kernels. Werk conducted in 1949 and reported by Splinter (19), indicates considerable variation of dielec- tric constant between the various components of the wheat kernel. Except in cases of extremely rapid heating, however, the conduction of heat between various parts would prevent any great temperature variation within the wheat. Moisture content must be considered and its effect on rate of heating determined. For all practical purposes the range of moisture content which may be encountered at time of treatment can'be considered to be from 10 to 14 percent (wet basis). It is possible that the effect of this variation will not be significant. 29 The variation of chemical composition of various types of wheat may also have an effect on their heating characteri- stics. The seriousness of any of these effects of variables will depend upon how critical the temperature margin is. Kernel size, color, and surface condition will have little, if any, direct effect on the rate of dielectric heating as they do in use of radiant heat. ‘There are various types and sizes of radio frequency generators which are designed for heating. Such a generator must have a high power capacity and.many common RF oscillators are not so designed. The cost of equipment for wheat treat- ment would be quite high, but not so as to make it impractical for use by elevators and seed companies. This review of literature revealed a considerable need for an efficient and effective method of treating seed wheat for loose smut. Former treatments and past investigations indicated that heat is an effective agent, but methods of application and control were difficult and impractical for common use. Infrared and dielectric energy both appear to have possi- bilities for the application of heat. Whether or not the variables involved in these methods are serious handicaps .depends upon the temperature range between the critical temperatures of the wheat and smut. With.these factors in mind, it seemed logical to design and perform tests to determine the following: l. 2. 3. 4. 5. 6. 30 Whether or not dry heating methods would be effective. The critical temperature of the smut mycelium for each method. The critical temperature of the wheat for each method. The effect of moisture content. Methods for measuring and controlling temperature. Whether any other effects were caused on the wheat or its development. In general, then, the purpose was to determine whether these methods satisfied the requirements of being effective and practical and, if so, to deve10p methods and equipment for their application. 31 TESTS OF TREATMENT WITH INFRARED RADIATION Objectives Previous preliminary investigations conducted by Lucas (9) had indicated that infrared treatment of wheat could be effective for the control of loose smut. It had not been determined, however, what temperatures were necessary for effective smut control or what temperatures were critical from the standpoint of decreasing the viabi- lity of the wheat. In view of these facts, it seemed neces- sary to conduct further preliminary tests to determine these critical temperatures. It also seemed desirable to determine the effect of varying the time of exposure to radiation. As in wet treatment, it was possible that lower temperatures would be effective if maintained for longer periods of time. The rate of temperature rise was also considered as a factor which might have an effect on the required temperature. Other factors which were to be investigated to determine their effect on this method of treatment were the variety of wheat, the color of wheat, and the moisture content. It was believed that color and moisture content at least would have a very significant effect on rate of heating and possibly on the critical temperatures. 52 Apparatus and Equipment The reflector type heat lamp was chosen as a generator of radiant energy because it is inexpensive, easy to control, available in various sizes, and would be practical for larger scale Operations as well as small tests. The wave lengths of this lamp fall in the shorter end of the infrared band and this was believed desirable from the standpoint of penetration. Apparatus as illustrated (Figure 8) was constructed so that the lamp was mounted above and directed down toward the ‘wheat sample. Provision was made for adjusting the height of the lamp and for the addition of more lamps, as desired. A switch.was included in the wiring for control of the lamp. The surface upon which the wheat was placed was heavy canvas belting, cut 14 by 18 inches, and placed over number 12 gauge hot rolled steel. The steel was supported one-fourth of an inch above its wood background to provide an air space for insulating purposes, to prevent conduction of heat into the base of the apparatus. The belting over steel combination was used because it was believed that such a combination might well be used in a continuous process machine, if such were ever develOped. Temperature measurement was the problem.which was of primary concern because the accuracy of this measurement could well determine the success or failure of this treatment. name» mzapmon panacea new mom: nauuacaad '!’I'"'||'|" l""'"-"|ll 13$ )5... \ciw \k bk\\c&, -_.MNLW ROSS w. K; \Sv‘b k 3. Lurk wbhd m. hQLDek. .m enemas 3 in 34 It was decided to try to insert a copper-constantan thermo- couple into a kernel of wheat and place this kernel randomly in the test sample. A satisfactory thermocouple was made by butt welding number 30 copper and constantan wires. Kernels of wheat were then drilled longitudinally with a number 80 drill and were strung over the thermocouple wire. The couple was placed in the center of one kernel, and five other kernels of wheat were placed over the wire on each side (Figure 9) to prevent heat from being conducted into the thermocouple by the wire. A Leeds Northrup potentiometer was used to measure the millivolt potential across the couple. This reading was then converted to equivalent degrees Centigrade by means of prepared tables. Test Procedure Before treatment by radiant heat, each sample was tested for moisture content by the Steinlite capacitance-type meter. The wheat was then placed on the canvas in a single layer and arranged roughly in a circular spot, the diameter of which.varied from two to four inches depending upon the size of the sample needed. The kernel in which the thermocouple was placed was located near the center of the sample. In nearly all tests a 250 watt lamp was used for heating at various heights. The height of the lamp was taken to be the distance from the extreme lower end of the bulb to the exposed surface of the wheat. A thermometer was laid on the 35 Figure 9. A kernel of wheat was placed over a butt-welded thermocouple. Extra ker- nels were strung on the wire to shield it from direct radiation. 36 canvas (Figure 10) with its bulb extending into the edge of the wheat samples. This was to determine the correlation, if any, between a thermometer reading and the thermocouple reading. It was realized that the thermometer would respond to direct radiation and that very probably two different thermometers would read differently after direct exposure to infrared radiation. The following readings were taken for each test: 1. voltage at the lamp 2. room temperature 5. lamp height 4. moisture content of wheat 5. initial temperature of wheat 6. final temperature of wheat 7. time for heating in seconds 8. thermometer reading on canvas surface. Also the variety and age of the wheat samples were recorded. After removal from the treating apparatus the wheat sample was placed in an envelOpe and allowed to cool slowly to room temperature. The samples were then tested for germi- nation by placing one hundred kernels on moist filter paper in petri dishes. Some of the treated samples were then planted in field plots for determination of degree of smut control. Tests Conducted Heatigg rate determination. Preliminary tests were run to determine the rate of heating with the lamp adjusted to 37 Figure 10. Radiant heating apparatus and measuring instruments 58 various heights. The temperature was read each 15 seconds, during the heating period, and these readings plotted as shown (Figure 11). The purpose of these curves was to give an indication of what lamp heights might be necessary. The curves indicated that in order to hold any given temperature for a period of time, it would be necessary to very accurately adjust the height of the lamp. There would, of course, be an equilibrium temperature, for each lamp height and ambient temperature, at which the heat loss would equal the heat gain by radiation. Both Ybrkwin (white) and Fairfield (red) wheats were used and, as is indicated by the curves, the red wheat heated faster in all cases. The wheat was heated only to 55 degrees Centigrade because at that time it was believed that such a temperature would be effective,as in wet treatments. Determination 23 the critical temperature 22,32355. Fifty-two tests were conducted to determine what temperatures were harmful to the viability of wheat. These tests were conducted as explained under "Test Procedure." The first 18 samples were heated to temperatures of between 50 and 60 degrees Centigrade. This temperature range was selected on the basis of previous methods of treat- ment. The germination tests of these samples revealed no significant effect on germination percentages by any of the temperatures used (Figure 12). 59 55 + + ..... ~ 3‘ ATM/CHE: / ”" ./ Leanna: § 50 F / 8 t5 / E 2:44J> t... is (L 40 * YORKW/A/ g __ _ FAIhF/ELD is 35 FE Mu {L 30- )3 K1 ’\ :5 a n . J o 256 400 600 504 Figure 11. TIME (5560/1/05) Time-temperature curves as affected by color of wheat and height of lamp nowadagew co 959939.89 Mo pooumm .NH 0.3m?“ MQVQQRRMG .. MESK xQMszk mm: e: as om om S no me 4 1 14 Gm R. m u azmakoro mtoxwxoz 0‘ 9 3 a s M N V a 5 fl 8 #0 QLQSO U o o . it!!! . cox 41 Eighteen more samples of these same varieties, Yerkwin and Fairfield, were then treated with.higher temperatures, ranging from 60 to 120 degrees Centigrade, in an effort to determine the general range of the critical germination temperature. These tests indicated that this temperature was between 80 and 90 degrees and germination was very greatly reduced by temperatures over 100 degrees Centigrade. These temperatures and germination percentages were also plotted (Figure 12). Additional tests were run to further narrow down the critical germination temperature using American Banner and Goens (red) varieties. Wheat used in these tests was smut infected and of the same supply which was to be later used for field tests on smut control. The moisture content of these samples was modified to 12 percent from about 8 percent. Because it was estimated that the moisture content of fresh seed wheat at planting time would be about 12 percent, all test wheat was adjusted to that percentage. The critical germination temperatures for these varieties at 12 percent moisture content, as tentatively determined by these tests (Table I), were: American Banner - 84 degrees Centigrade Goens - 81 degrees Centigrade The height of the lamp in these tests was eight inches. Effect 23 moisture content 22 critical temperature. Another series of tests was conducted to determine whether 42 TABLE I EFFECT OF‘TEMPERATURE ON GERMINATION Degrees Percent Germination Centigrade American Banner Goens 8O 89 -- 81 96 92 82 92 71 85 9O 65 84 85 67 85 -- 62 86 46 71 87 42 64 88 51 44 89 51 28 9O 28 20 Control 98 94 43 moisture content had any effect on critical germination temperature and, if so, just how much. These tests were run on samples of wheat of various moisture contents of 10, 15, 18, and 25 percent. The original moisture content of the wheat was modified by applying known amounts of water to weighed samples of wheat in closed containers. The samples were then left 24 hours to allow them to come to a uniform equilibrium moisture content. The results of these tests, as illustrated (Figure 15), show significant differences in the effects on germination caused by high temperatures. The critical germination temperature appears to be lower for wheat of a higher moisture content. Eigld'gggtg}g£_gmut_control. After the preliminary tests for determination of heating rate, critical temperature, and effect of moisture content, it was felt that before further work was done along these lines, some field tests should be set up to determine the effectiveness of this treatment for control- ling smut. If radiant heating should prove to be an effective treatment, there would be a need for extensive tests along the lines of all these preliminary tests. The varieties of wheat selected for the field tests were American Banner and Goens, white and red wheats, respectively, and because these varieties had been used for determination of critical germination temperatures, these temperatures were 44 /00 ‘0 Q C!) Q 05 Q / / if PERCENI' GER M/N/V/O/V V o 83 0 6'0 7 40 ~90 If 80 85 70 if 7EMF’ERATU1‘PE' CENT/GRADE Figure 15. Effect of moisture content on germination after heating 45 used as a starting point for the various treatments. The critical temperatures, as discussed previously, were used as one treatment temperature and six other samples were treated at various temperatures, two degrees apart, both above and below this critical temperature. This was done for both varieties and, including the control, there were 16 different treatment samples. For American Banner the treatments were 78, so, 82, e4, 86, as, and 90 degrees Centi- grade. For Goens they were 75, 77, 79, 81, 85, 85, and 87 degrees Centigrade. The lamp used for these tests was a 250 watt industrial heat lamp which was placed 10 inches above the wheat. The wheat used was of the same smut infected supply that was used for preliminary tests and its moisture content was adjusted to 12 percent for all tests. The kernels of wheat on the thermocouple wire were replaced and freshly drilled for each test, and the kernel which.was placed over the couple was selected randomly from the sample to be treated. Four hundred kernels were taken from each treated sample to be used for planting in field plots. Exactly one hundred kernels were planted in each test row and they were spaced about two inches apart, making 16-foot rows. There were four replications of each treatment and the rows within each repli- cation plot were arranged randomly for statistical analysis. Eight treatments of two varieties made 16 rows in each of four 46 replication ranges. Border rows were planted along the sides of the test plots for protection against outside influences. Three weeks after the plots were planted, counts were made of the number of plants which had emerged in each of the 64 rows. In May of the following spring, counts were made of the number of plants which.had survived the winter in each of the test rows. These data are summarized in Tables II and III, and in Figures 14 and 15. As soon as the wheat headed out and reached the necessary state of maturity, counts were made of the total number of heads and the number of smutted heads in each row. From these counts the percent of smutted heads was calculated and plotted against treatment temperature. Discussion 2; results. As is indicated by the curves (Figure 14), the 90-degree treatment was effective in con- trolling smut in American Banner. There was no incidence of smut in any of the replications of this treatment. However, the next lower temperature, 88 degrees, was not completely effective. The percent of smutted heads appears to decrease with temperatures above 82 degrees Centigrade. Both the percent of emergence and winter survival data form relatively smooth curves when plotted against treatment temperature, and there is a considerable decrease in both at the temperature which was effective in the control of smut. 47 mob mm mom mm hm U n. H mmm mm Nb o d.& OH mmn mm me Q ¢.¢ NH How mm #m a 0mm mm m O.N w mom mm mm c 0.0 b 00H mm Hb o H.n b mmm mm mm D N.N m wNm hm mm a man mm o O O bmH mm No 6 o 0 wow mm mm o O O an an on n O O ¢®H Om mm m Hmm om b n.m ma man we mm c m.m an man no am 0 #.® Hm bmn mm mm Q mew mm now mm mm d HOHuGOU w modem modem modem Hepabanm oonow seduce Ampnooemv can» 909852 oeupzam poppdEm Hence henna; usefim Iaaaom mafia Isaemace psofipmoaa useoaom ucooaem pceonom Edam BzmHmdm mBHB QWBH>ASm oonew :oHpmo Ampcoeomv can» 909852 poppSEm copudam Hapoa pepcfia Iaofim IHHmom mafia tumomaoa pnofipmoha unooaem pneoaom pqeoaom Ammszezoov HH mumaa /00-?-—- 'v i [ r i l ‘ A 'l 1 i Y’fi' ’ l 80 r- I’ V I’ ’ ‘ - Su» w'ml 6CH+~ ~ - i a i E i a ' * ; +0L— *"‘ l“ L 0‘ ! £0 __ . I o , 1 1 (I w . i V i 1)» _____ + z. _ Sun/fret) Head: j 0 L._ .. _. ._ l‘ A m cmvmoz.‘ .75 so 8; 84 '83 as we TEMPERATURE ‘- C‘ENf/GfMflE Fi re 14. Effect of temperature on emergence, surviva , and smut control of American Banner wheat. 5O o 0 man on Hm U H.m ma ebn mm mm o H.H w mmn om mm a o 0 man am we a mew nm ma w. H mom no me o o 0 can we om o m. ma nmn we be p m. m Haw Nb mm m ore mm ea 0 0 mon em as e o 0 new as am e o 0 8mm ow or n o 0 wow am as a new rm ma H.m 0 mon mm be p m.m w men we «m o m.m 0H own mm mm o m. n men mo mu m Hoapsoc ma mnecm modem modem Hepabazm cescm soapeo Amesoocmv can» acnaaz mouussm moppsEm Hence nousaa spasm .uaaacm mafia neacasoa escapeoaa useoaem pneumom usevom B¢mm BZdHQ¢m mBHB QMB.H a ban mb mm a mHn mu m N.H w own mm as U m.m m mbn rm mm o o o bmn mm mm 3 o 0 ran mm mm s new bb OH m.m HH mun mm mm m m.m m mmn mm mm o o 0 mon bb mm D o o own ow mp m won or HH H.N m men em up u o o mHn mm or o ¢.m m can rm Hm n o 0 mm» pm me a 00¢ Hm NH upwem modem mpmom He>H>a5m modem defines Ampqoocmv was» honapz vmppSEm menussm Hence aocha macaw IHHaom oEHB umaemfiea pcoEpwoaa paeoaom useerm psooaom A AQHDZHBZOUV HHH mqm¢a /00r---—- T i T i I E 1 5 xi lefyé’f'Ce ! 1 l L. i | l I . | SC: r vivq.’ I N I ' 1 a F “x i i ! 's .I‘ . \ ‘ i a i _ L D » ——«———G> “fwd—«e»- . {J 7 QT . t 11 J 2 f 1 Need ”8 {d5 (x A?) . " \i 0L-l- i n C‘ 0A 77: ii 75 77 7 x’ 6 l ’6]- 3 c 5' 5‘ 7 R5%FERATUR£"CZ%UVGR%DE 1F~ ~ ‘ ‘ Figure 15. Effect of temperature on emer- gence, survival, and smut control of Goens wheat. 55 TABLE IV SUMMARY OF FIELD TEST DATA (AMERICAN BANNER) Treatment Time Percent Temperature (Seconds) Emergence Smutted Heads Control 0 85 7.6 90 481 65 O 88 516 68 2.7 86 450 75 5.8 84 420 77 2.6 82 570 84 5.2 80 290 86 5.5 78 270 84 6.5 TABLE V SUMMARY OF FIELD TEST DATA (GOENS) Treatment Time Percent Temperature (Seconds) Emergence Smutted Heads Control 0 81 1.9 87 475 77 O 85 470 80 ' .4 85 448 82 1.6 81 400 77 1.1 79 565 85 1.5 77 555 84.5 .9 75 515 87 1.1 54 This is undesirable and would have to be either eliminated or compensated for in rate of seeding, if the treatment were to be used on a commercial basis. The Goens results, as plotted (Figure 15), were quite similar to the American Banner in that the highest tempera- ture treatment, 87 degrees in this case, was the only totally effective treatment. There were no smutted heads in the plots which had been treated at that temperature; however, there was a very low percentage of smutted heads even in the control plots, which was undesirable. The previously expressed belief that there might be a wider range between the effective killing temperature of the smut and that of the wheat germ than there was in hot water treatment, was not supported by the test results of American Banner. In the Goens tests, however, there was very little damage to germination by treatments which were effective in killing the smut. It may be, therefore, that slightly higher temperatures could be used without serious damage to germination, with this particular variety. It is felt that in the use of radiant heat there might ‘be considerably higher temperatures at and near the surface than nearer the center of the kernel. Because the germ of the wheat is near the surface, it is subjected to higher temperatures than the smut mycelium which is nearer the center. This would be true in the case of kernels which were lying with the germ side of the kernel exposed to 55 the radiation. If this is true, it could have a serious effect on germination, especially if rapid heating rates were employed. Either heating the wheat slowly or arranging the kernels with the germ down would appear to decrease such damage. It might be possible to arrange the kernels in the desired manner by means of a vibrating screen. Because the height of the lamp remained constant for all of these tests, the temperatures of the various treatments were directly affected by the time of exposure. It seems possible that lower temperatures might be effective in control- ling smut if maintained for longer periods of time. This could be accomplished by increasing the height of the lamp. The tests, however, were not performed in such a way that the effect of time of exposure could be determined. In both.American Banner and Goens the relationships between winter survival and emergence are nearly constant for all treatments. This would indicate that there was no weakening effect on the wheat that germinated which would cause it to winter-kill more easily. 56 TESTS OF TREATMENT BY DIELECTRIC HEATING Objectives Preliminary studies and the review of literature revealed certain facts about dielectric heating which indicated that it might have advantages over other methods of heating for the treatment of seed wheat. One of these characteristics, due to the nature of the heating process, is that the heat is generated within the material to be heated and would, there- fore, tend to create a very uniform temperature. Also it was indicated that physical variables within the wheat, such as size, shape, color, and condition of surface, would have less influence on the rate of heating than with radiant energy. Another apparent advantage of dielectric heating over radiant heating was that the wheat would not have to be in a single layer but could be in larger lots of considerable thickness. If either of these methods were ever to be developed into a continuous process for commercial use, this could be a very important factor from a practical engineering standpoint. The purposes of these experimental investigations were, then, to determine whether or not dielectric heating would be effective in heating wheat and in turn effective in smut control. Also, it was necessary to determine the temperatures involved in the use of this method and the effects of other 57 variables, such as moisture, type of wheat, frequency, and rate of heating. The effect of high frequency itself on the viability of wheat was not known and the review of literature indicated that one of two seemingly Opposite effects might be expected. The germination might either be drastically lowered or it might be stimulated. Another objective was to design experimental apparatus which would be workable for these tests and which could give indications of what might be practical for equipment for larger scale treatments. Determination of Electrical PrOperties of Wheat Before the power, voltage and current requirements for heating a given sample of wheat could be calculated, it was necessary to determine the values of such things as dielectric constant, power factor, loss factor, and specific heat. The loss factor could be calculated as the product of the power factor and dielectric constant, once they were determined. The specific heat of wheat was given by Stahl (20) as ranging from..59 for 9.5 percent moisture content to .51 for 21.2 per- cent moisture content. A Boonton type 160-A Q-meter (Figure 17) was used to measure capacitance and Q, which.were sufficient for the calculation of dielectric constant and power factor. A test capacitor (Figure 16) was designed and built for use with the 58 Figure 16. Test capacitor used for determining dielectric characteristics of wheat Q-meter for these measurements. The capacitor was designed to have a capacitance of approximately 100 micromicrofarads using an estimated dielectric constant of five for wheat. The formula for capacitance, as given by Brown (4), is: r.. 8.4 .__ (4) 7‘ fi4JW/0’d where A1=area of capacitor in square inches e :dielectric constant d.=distance between plates in inches then A: -5545’20‘ 0" If C =100 micromicrofarads d =.555 inches (assumed) e :5 (estimated) then A=£?.6 Squad-I- [flehsd The test capacitor was constructed so that the area of the smaller plate was 50.4 inches and the distance between plates was one-third inch. The smaller plate was 5.5 inches square and the other plate was made 8.5 inches square to decrease the fringing effect. Aluminum foil was used for the plates and was fastened to the plywood backing with vaseline. Terminals were extended through the plywood from the center of each plate and short, heavy wire leads were used between the capacitor and the Q-meter. The capacitive effect of the leads was minimized by making them short and large and by having them in nearly the same position at all times. 60 Figure 17. Boonton Type 160-A Q-meter used for determining dielectric characteristics of wheat. A suitable coil was selected which would give resonance of the circuit both with and without the test capacitor, and this coil was connected to the proper terminals of the Q-meter (Figure 18). The test procedure was to adjust the variable capacitance of the Q-meter to give a maximum reading on the Q-dial at a frequency of ten megacycles per second. Ten mega- cycles was used because it was the fixed frequency of the dielectric heating unit to be used in later tests. The Q—meter was adjusted for maximum readings of Q, both with and without the test capacitor. The following readings were made and recorded: Cl - Capacitance dial reading without the test capacitor C2 - Capacitance dial reading with the test capacitor Q1 - Q reading without test capacitor Q2 - Q reading with test capacitor. These values were sufficient for the calculation of both the dielectric constant and power factor. Using formula (4) the dielectric constant is: e: 4.4:. 10‘. d0 A and since d: .555 inches A.:50.4 square inches C :(Cl-Cg) micromicrofarads then s .0468 (Cl "C‘) (5) )2 (\ I.) -_1..- C R, --l__ I R I l 2 I I . I ‘7 ,.....-...-_.-A --__-J i l V 94" 63:01.; Aft-w Figure 18. Diagram of the Q-meter circuit (‘D CA The formula used for the calculation of power factor is: R F : :-----.._— (6) 53x "/ where Q s : __Q.L_0L .. . Alisha. -' Q: ' at 0' When Qx is greater than ten, the power factor may be. considered to be the reciprocal of Q; with very little error. A series of tests was conducted to determine the dielec- tric constant and power factor of wheat and to determine the effect of moisture content on these electrical prOperties. Vigo wheat was used for these tests because it was available in ample quantities and was considered representative of common varieties. The moisture contents of samples of wheat were modified according to a procedure previously explained. The samples were then placed in the test capacitor and measure- ments and calculations were made to determine the quality factor, dielectric constant, and power factor. Calculation of Power Requirements It was decided to use one-half pound samples for the test treatments with dielectric heating, because by using samples of that size the electrical quantities involved would be easier to control and measure than for smaller samples. Also the significance of such effects as fringing of the electrostatic field at the edges of the sample and heat conduction away from the surfaces would be much less for 64 TABLE VI RELATIONSHIP BETWEEN MOISTURE CONTENT AND DIELECTRIC CONSTANT Moisture Content Dielectric Constant 9.81 4.74 10.20 4.78 12.12 5.12 13.60 5.51 16.69 6.05 19.65 6.69 21.40 6.97 r\ ”a . I + Fag) l ,fi‘ / C“ 'W L i/t' I“. ‘ a A IV. .f‘ (1 ) L- If '— " ’ ’RV'“ _"_T—“"'—' W- ”__-‘—T i l / f, /’ I/ l / I/ / a. 'I / / b / / .4 l / . ‘ A / Dxezeéfr/C on: // ; G, / i . l v -« f n ' Fl C T/‘f } O x ; \ 4 1.-.--- _-. 1.-- -.-_._--. .-1-...-.._.. 3 .5 /; /[ .s' 7J/57é/FfE C(SNTENT (wzr baa/5) Figure 19. Effect of moisture content on dielectric properties of Vigo wheat i 3 R: Q larger samples. Larger samples than one-half pound were not used because of the very limited supply of wheat, which was uknown to be highly infected with smut, and because only a few grams of seed were needed for testing germination and smut control. All the following calculations are for a one-half pound sample one inch thick. The power required for such a sample would be, according to equation (1): P = 1.75 z 10”" #100743) By assuming a heating period of three minutes for a one-half pound sample of wheat at 12 percent moisture content and a temperature rise of 75 degrees Centigrade, the power requirements were calculated as: P = [.76 uo"‘x.5: 7: L; :./‘2 where C :.41 for 12 percent moisture content. The voltage gradient could then be calculated by using equation (2). The volume of one-half pound of wheat was taken as 18 inches for the purpose of calculating power required per cubic inch. kg 5' ‘2 l4: Io"'fe" t where ”3% = $0 watts/cubic inch f 2 frequency 8 10 megacycles 3”: loss factor: . 4£ then 5, = he J 5' I volts/inch 67 By using equation (5) the current through the dielectric was calculated. I: 1.4 now £. fa f— where e : dielectric constant = 5.12 A.:area :18 square inches d.=thickness :1 inch then I: I. 6 0 amperes Apparatus and Equipment The calculated values of voltage and current were very reasonable and moderate, so the eXperimental heating apparatus was designed according to the assumed conditions. The circular plates were made of galvanized iron and were nine inches in diameter. They were mounted on one-half inch thermal insula- tion board which was backed with one-half inch plywood. The lead terminals were extended through the insulation and plywood in porcelain insulators. The bottom plate assembly was fastened rigidly in the framework (Figures 20 and 21), while the upper plate assembly was hinged for convenience in placing and re- moving samples. The distance between plates was exactly one inch and the plates were in direct contact with the sample when in Operating position (Figure 21). Very light cardboard was used for the sample retaining ring because it had a low heat capacity, was rigid enough to hold up, and was a dielectric material with a dielectric constant (5.5) similar to wheat. The diameter Figure 20. Wheat was placed in and contained by a cardboard ring Figure 21. Close-up view of plates with sample in place 69 of this ring was 4.78 inches, giving it an area of 18 square inches and a volume of 18 cubic inches or one-half pound. The source of power used was a Westinghouse industrial radio-frequency generator (Figure 22) with a rated capacity of one kilowatt. It was adjusted to oscillate at 10 mega- cycles, which was its design frequency for dielectric heating. The plate assembly was connected to the generator through an external radio-frequency ammeter for direct reading of current. A simplified schematic diagram of the generator circuit with the load is shown in Figure 24. Temperature measurement with this method of heating was a serious problem. Thermometers could not be used because they were a dielectric material with different dielectric «constant than wheat and would, therefore, read the temperature 10f the glass and not that of the wheat. Calculation of tempera- ‘ture from electrical measurements and the properties of the wheat would be subject to many sources of error and was, there- :tore, considered unreliable and impractical. A thermocouple seemed the most desirable device, although it also would be influenced by factors other than wheat temperature which might affect its reading. The fact that the thermocouple wire was 'both a good thermal and electrical conductor introduced a source of error when used in a high frequency field. It was decided that this was the best available method, however, and a copper constantan thermocouple was used. The leads were of number 50 ‘Wire and were twisted to minimize the effect of the field. 70 Figure 22. Dielectric heating apparatus and measuring instruments Figure 25. Sample of wheat being prepared for treatment _.7’../£R 5.9)" .’.r 0, 7L" . .571. fiME V7' VOLT/1 [v5 Figure 24. Schematic diagram of grounded grid Hartley oscillator circuit for dielectric heating. 72 The potential was measured with a Leeds Northrup potentio- meter and converted to temperature readings with standard tables. A zero degree reference Junction temperature was maintained with ice water in a thermos bottle. Test Procedure Each supply of test wheat was tested for moisture content before treatment. As in radiant heating tests, a Steinlite moisture tester was used and the average of several readings was taken. Moisture content is significant in dielectric heating because of its effect on dielectric constant, power factor, and specific heat, as illustrated in Figure 19. Exactly one-half pound (227 grams) of wheat was used in each treatment. It was poured slowly into the retainer ring and leveled off with a straight edge (Figure 25) in an effort to obtain a uniform density throughout the sample. The thermocouple was entered through a small hole in one side of the ring and was placed in the center of the sample, midway between the plates. After the power was turned on, the power control knob was adjusted to create a constant current of two amperes t"hiccugh the wheat. Attempts to use three amperes resulted in ElI'czing between the grounded plate and the thermocouple. When the potentiometer indicated a predetermined, desired reading the power was cut off and after a period of 60 seconds the temperature was read again. This second temperature reading 73 was taken because erratic results in preliminary tests indicated that the reading at the time of cut-off was influenced by the electrostatic field. A sample consisting of approximately 50 grams was then removed from the center of the larger sample. It was placed in an envelope and allowed to cool slowly. Data taken and recorded during the treating process were: 1. initial temperature 2. cut-off temperature 3. temperature one minute after cut-off 4. moisture content 5. heating time in seconds 6. current through wheat 7. room.temperature 8. age and variety of wheat. The small treated samples were used for germination tests and in some cases for field tests of smut control. As with radiant heated samples, the germination tests were conducted with 100 kernels placed on moist filter paper in petri dishes. The counts then automatically represented percentages. Tests Conducted Determination 2; critical temperature gg'wheat. A series of 56 preliminary tests was performed over a wide temperature 74 range to determine the temperatures at which germination was decreased. Yerkwin wheat was heated to various tempera- tures such that the temperatures 60 seconds after the power was cut off ranged from 56 to 100 degrees Centigrade. The current was kept constant at two amperes throughout this series of tests and the moisture content of the wheat was 9.8 percent. Germination tests revealed a wide range of germination percentages for temperatures in this temperature range. As is indicated by the curve (Figure 25), the germination dropped sharply with temperatures over 90 degrees. This critical temperature is several degrees higher than for the same variety of wheat treated with radiant heat. The fact that the temperatures indicated were taken 60 seconds after the heating stopped must be considered, as it is very probable that the maximum.temperatures reached were somewhat higher. Determination 23 actual EEETEEE temperature. The lack of any consistent relationship between heating time and cut- off reading on the potentiometer indicated that this reading was not the true temperature of the wheat. This indication was substantiated by the fact that there was a reasonably consistent relationship between heating time and 60-second temperature (Figure 27). In an effort to determine the approximate difference between the actual cut-off temperature and the 60-second M/A/A T/Cx/J Aff' (257? r L.- ‘— 95/10 I“! M K c.____ (I ’4 u )r‘ ,2! x CON 7301. 60 7c: 80 9o "/35: 7EMPERATUHE - CENT/GRADE (so asco/vos Af‘fE/i’ Cur-OFF) Figure 25. Effect of treatment temperature on germination of Yorkwin wheat fi/TATURE ‘ C if." TIGHADE —‘ I 7f77f' Ch 0 Q? (b N m if 70 L 1 L 1 1 v i L i 1 l 0 ll“ 2r 3:7 40 5.." 60 70 an 7a we no we SECCNDJ‘ AFfE/C? 60735»??? Figure 26. Cooling curves of two samples after potentiometer indicated 86 degrees at time of cut-off. 77 temperature, a series of tests was conducted in which the rate of cooling was checked for two minutes after the heating period. The wheat sample was left in the closed heating unit and temperature readings were taken each ten seconds through- out this period. Nine different tests were run on three different cut-off potentiometer readings. There was no con- sistency in the drOps of potentiometer readings in the first ten seconds, but for the remainder of the 2-minute interval all cooling rate curves (Figure 26) were nearly identical. By projecting a smooth curve back through the first lO-second interval, the approximate initial temperature and the tempera- ture drOp during the first 60 seconds were estimated. The temperature drop was very close to six degrees in all tests. Even though a very close approximation of the actual cut-off was obtained by this method, a given cut-off temperature could not be reproduced, except by trial and error. EEElQHEEEE§H2£.EEEE control. Thirty-two samples of smut infected Illinois number 1-128 spring wheat were treated to various temperatures for field tests to determine the degrees of smut control. The results of previous tests (Figure 25) indicated that the critical germination temperature for dielectric heating was about 89 degrees Centigrade and, although the wheat used for field tests was of a different variety, the critical temperature was assumed to be the same. The 60-second treatment temperatures for the field tests, therefore, ranged from 77 to 99 degrees. ERA TUNE ‘ CENT/GRADE rm 7[/~// /€( 75... *A / 75 A I L I l J I L i A; a 354 we 500 60c“ 65: HEAT/N5 T/NE / 5550/1/05) Figure 27. Relationship between heating time and 60-second temperature for Illinois number 1-128 wheat, with a current of two amperes. 79 The treating procedure was the same as described for previous tests of dielectric heating. The current through the samples was maintained at two amperes and for comparison purposes the 60-second temperatures were used. For reasons previously stated, it was impossible to exactly reproduce any given temperature, and there were, therefore, very few temperatures with.more than one replication. Germination tests were run on the treated samples in the laboratory prior to planting in the field. The results of these tests were plotted against 60-second temperatures (Figure 28) to illustrate the effect of temperature. One hundred kernel samples were then planted two inches apart in 16-foct rows. These rows were arranged randomly to provide for statistical analysis of results. Two border rows were planted on each side of the test plots as guards. Because of soil conditions at the time of planting and shortly after, the emergence percentages of all plots, includ- ing the controls, were extremely low. The soil was extremely hard, lumpy, and dry in the bottoms of the furrows in which the test samples were planted. These conditions were believed responsible for the wide scattering 0f points on the emergence curve (Figure 28). Because of this scattering, the validity of the emergence curve is extremely questionable. Emergence counts were made 25 days after planting on June 4, 1951- After the wheat was headed out, counts were made or the total number of heads in each of the rows, as well as the number 80 m.® OH ¢mH ow mm Ham H.nm mm o 0 en ma mm wee m.nm Nm m.¢H an mam mm mm nbn o.¢m Ha w.¢ n mo mH mm mmfi o.¢m ON. 0 0 mm on mm Hmv o.ma mm $.m w mw om mm mow- ¢.mm . ma 0 o kw Hm em mum m.wm 0H 0 O «a 0 OH me 0.00 mm 0.0 0H mam rm mm Honpcoo «.ma ma mm mm em Honpsoo m.e a an” en em . 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AQMDZHBZOOV HH> mqmda PE/H‘CEA/7 83 l00 - --' f it 2.. 1 ° i is 1 . ° D o 2 F 60 L .. _1_ .------ - V c 65-» ~ T i a ‘ p l l D a 4m - _.. -. L D 7 { a | s » l ! I ; "r em en- a r ' " i . 41 ‘ IX ' A “"1- 43H 1 i g . I 5"772/f78dHe7d15‘ E l i x x ,u I . ‘ L1 1‘ xxx { K O b ._.: 4‘ J ' ~ J_. x x .1. cavrfifil 80 8 4 88 9.3 we TEMPERATURE "' CENT/GHADE (G‘O‘SICOND ) Figure 28. Effect of temperature on Illinois number 1-128 spring wheat with dielectric heating. 84 of smutted heads. These data, along with the heating times and temperatures, are included in Table VII. The percent of smutted heads of the total number of heads was calculated for each test and was plotted against treatment temperatures (Figure 28). The remainders of the one-half pound treated samples were also planted in the field with a small hand drill. Because there was no accurate control of the number of seeds or the distribution in the rows, total counts of emergence and stand were not made. Counts were made, however, in 2-foot sections of each row. Smut incidence of the entire row was observed. The counts of smutted heads in these plots showed no plot to be entirely free of smut. This fact does not support the results of the space-planted test plots. Discussion 33 results. As is illustrated in the germination curve (Figure 28), the germination drOpped with temperature over 90 degrees. However, the germination did not drop as sharply as in the case of Ybrkwin wheat in pre- vious tests (Figure 25). Even.with the higher temperature of 95 degrees the germination was not too low to be tolerated, if such a treatment were to be used for smut control. The data indicate that treatments of 95 degrees were effective in smut control. The fact that the field plots, which.were planted with the remainder of the one-half pound sample, did not support this indication should be considered, 85 but it is believed that there are logical explanations for it. The loo-kernel, space-planted plots were planted from samples taken from the center of the one-half pound treated samples. The thermocouple was also placed in the center of the sample, so the temperature read was that of the area from which the smaller sample was taken. Because of fringing effects and heat conduction into the plates it is possible, if not probable, that some of the wheat did not reach the measured temperature. The greater smut incidence in the larger plots is believed due to this fact. As was discussed under radiant heating tests, it is possible that lower temperatures might be effective, if longer heating periods were employed. It would, however, be difficult to maintain a constant temperature for a period of time with this dielectric method of heating. The method used for temperature measurement was not at all satisfactory. It is believed that it might be possible to enclose the thermocouple and its leads in a shield to pro- tect it from.the influence of the electrostatic field. Whether or not a method can be developed for using a thermocouple, some method.must be perfected for the direct and accurate measurement of temperature during the heating period, if this treatment is to be practical. 86 SUMMARY AND C ONC LUS IONS There is a need for an improved method of treating wheat for loose smut. Most of the undesirable features of known methods are attributed to the fact that the wheat is soaked in water during the treating process. A method of "dry" application of heat would be much more practical and accept- able than the water bath, if it were as effective. The review 01' literature and previous work indicated that "dry" treat- ments might be effective. The tests conducted on radiant and dielectric heating indicated that either or both of these methods might well be used in an effective treatment. There is, however, a need f°P continued work and investigation of these methods to date:r'mine the optimum temperatures, heating rates, etc. After these things are determined, there will be a need for the deVelopment of suitable equipment for the application of such t1‘eadnuents to commercial scale Operations. If dielectric heating is to be used commercially for tre ating wheat, it will be necessary to deve10p some method or Obtaining accurate instantaneous temperature readings during the heating period. The method used in these tests would not be at all satisfactory for general use, because any 83*an temperature can not be accurately reproduced. The general conclusions which were drawn from the ekilDerimental work of this project are: 87 Treatment with radiant heating. 1. 2. 5. 4. 5. 6. 7. 8. Red or darker colored wheat heats slightly faster than white wheat. The higher the moisture content of wheat, the lower is the critical germination temperature. The rate of heating can be effectively controlled by the size and height of the lamp. Thermocouples, placed inside kernels of wheat, are satisfactory for measuring wheat temperature. Radiant heating is effective in controlling smut at higher temperatures. The effective treatment temperature depends upon the characteristics of the wheat. There is a narrow temperature margin between the critical temperatures of the wheat germ and that of the smut mycelium. There is less drop in germination in red.wheat than in white wheat at temperatures which are effective in smut control. Treatment with dielectric heating. 1. 2. 5. Moisture content has a direct effect on the dielectric constant and power factor of wheat. Moisture content has an indirect effect on rate of heating. Physical factors, such as size and color of kernels, appear to have no effect on heating rate. 4. 5. 6. 7. 88 Thermocouples do not give an accurate indication of temperature during the heating period. Temperatures of 95 degrees Centigrade appear to be effective in smut control. The germination is greater than 80 percent in all treatments below 99 degrees Centigrade. There is no indication that dielectric heating to any temperature stimulates germination or grOWtho 1. 2. 5. 4. 5. 6. 9. 10. 11. 12. 15. 14. 89 LIST OF REFERENCES Attwood, Stephen S. Electric and Ma netic Fields. John Wiley and Sons,_Inc., NewYorE, I939. Boonton Radio Corporation, Boonton, New Jersey. Instructions and Manual of Radio Frequency Measurements. Brown, A. I., and S. M. Marco. Introduction to Heat Transfer. McGraw Hill Book Company, New York: I912. Brown, H. G., C. N. Hayler and R. A. Bierwirth. Radio Fre uenc Heating. D. Van Nostrand Company, New Yer , . Cox, J. F., and L. E. Jackson. Crop Management and Soil Conservation. ed. 2, John Wiley and—SOns, Inc., New York, 1948. Curtis, Frank W. Hi h.Fre uenc Induction Heating. McGraw-Hill Book ompany, New ébrfi, I931. Dickson, James G. Diseases of Field CroEs. McGraw-Hill Book Company, New York, 19477 Farid, J. A. Loose Smut. Yearbook of Agriculture, 395-6, 1952. Lucas, E. H. oral communication, 1949-1951. Lycon. To In. and E. G. Montgomery. Examining and gagging Grains. Ginn and Company, New Ybrk, 19IZ. Martin, J. H., and W. H. Leonard. Principles of Field Crop Production. The Macmillan Company, New York, I949. May, E. Industrial Hi h Fre uenc Electric Power. John Wiley and Sons, nc., flew York, 1955. Muncie, J. B. Common Diseases of Cereals in Michi an. giihigiEZStite CoIIege EiperImEEt Station, East Lansing, u . , 942. Nicholas, John E. Some Preliminary Investigations on the Dehydration of Fruits and Vegetables with Infrared Energy. Journal of the Franklin Institute, 256: 285-91, September 1913. '_""' 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 90 . Radiation Uses and Needs in Agriculture. —Agricu1turaI'Engineering, 29: 145-6, April 1948. Osborn, H. B., P. H. Brace and others. Induction Heatin . American Society for Metals, Cleveland, Ohio, 1946. Rather, Howard C. Field Crops. McGraw-Hill Book Company, New York, 1942. Sherwood, E. M. The Rapid Determination of Hay Moisture Content. Unpublished M. S. thesis, Michigan State College, 1951, 118 numb. leaves. Splinter, W. E. written communication, 1950. Stahl, B. M. En ineerin .Data gE_Grain Stora 6. American Society of Agr cu ura gIneers, Saint Joseph, Michigan, 1948. Tapke, Victor F. Diseases 3; Seed Wheat for Loose Smut. United States Department of Agriculture, Washington, Bull. 1385, 1926. . Wheats Highly Resistant to Loose Smut. YearbOOk 2: Agriculture, 765, 1926. . Wheat Loose Smut Infection Prevented 45y Arid CIimat . Yearbook 22 Agriculture, 397-8, 1932. Weitz, C. E. Lam. Bulletin. General Electric, Lamp Department, NeIa Park, 5510, 1946. ‘ Westinghouse Electric Corporation, Baltimore, Maryland. Induction and Dielectric Heating manual. \‘W. .‘F‘m' \ EIHIHUJIllljlllulllflli|||||||||||H|||l|l |l|||1| WI}! 93 03144 9 5