FHYSICAL FACTORS AFFECTING THE GERMINATION VITALITY OF WEED SEEDS By Donald M* Kinch A THESIS Submitted to the Sohool of Graduate Studies of Michigan State College of Agriculture and Applied Science In partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Agricultural Engineering 1953 ACKNOWLEDGMENTS The author wishes to express his gratitude to Professor Arthur W. Farrall, Head of the Agricultural Engineering Department, Michigan State College, for his helpful suggestions and for his bestowment of the Graduate Research Assistantship which enabled the author to complete this work* A deep sense of gratitude is also acknowledged to Dr. Walter M* Carleton, Professor of Agricultural Engineering, for his inestimable suggestions, constructive criticism, and encouragement during the entire course of the experimental work, and for his reading and helpful criticisms of the manuscript of this thesis* A debt of gratitude is also acknowledged to Dr. George P. Steinbauer, Associate Professor of the Department of Botany and Plant Pathology for his helpful suggestions and guidance, especially during the work on germination char­ acteristics of various weed seeds. Acknowledgment is also made of the unselfish assistance rendered the author by Professor Grant S. Bennett, Assistant Professor of the Department of Physics, during the work on the ultrasonic phases of the problem. The author is also indebted to the Farmers and Manu­ facturers Beet Sugar Association of Saginaw, Michigan for the research grant that helped make this work possible, and especially to Ur. Arthur Schupp and Mr. Perc Reeve of that Association for their encouragement and suggestions. Acknowledgment is also made to the Agricultural Sngineering Committee of the Detroit Board of Commerce for their interest and their research grant that helped make this work possible. PHYSICAL FACTORS AFFECTING THE GERMINATION VITALITY OF WEED SEEDS By Donald M. Klnoh AN ABSTRACT Submittad 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 DOCTOR OF PHILOSOPHY Department of Agricultural Engineering Year 1953 / i Approved * attcA hi. A DONALD M. KINCH ABSTRACT Hand labor is still required for weeding in the sugar beet row. This hand labor could conceivably be eliminated if some method were discovered or developed that would pre­ vent, or at least deter, the germination and initial seedling growth of the weed seeds in the soil in the sugar beet rows. It appears that even a temporary delay in weed seed germi­ nation and initial growth would allow the beet seedlings to get a head start and more adequately hold their own in com­ petition with the weeds for sunlight, soil moisture and plant nutrients. A solution to the problem of hand weeding in the row is proposed. It is proposed that a strip of soil be physically processed so that entrained weed seeds be either killed or retarded in vitality and that this strip be laid down directly over the beet seed row at the time of planting. A detailed study was first made of the physical factors affecting seed germination, so that the requirements and limitations of physical processing would be known. Next, an investigation of three methods of physically affecting germination vitality reduction in weed seeds was made • Ultrasonic Energy — Reduction in vitality was obtained by exposure of mustard seeds in an ultrasonic field. The effect on the seeds was found to be largely thermal heating. DONALD M. KINCH Heat Energy — ABSTRACT The time-temperature relationships for mustard seeds in various stages of germination were obtained. This data determined the temperature and heat requirements for this method of physical processing. Mechanical Energy — Specified impact damage to the seeds entrained in soil samples was affected by a specially con­ structed semocidometer. Data obtained by use of this instrument permits the design requirements of a machine to be formulated utilizing this method of soil processing. Third, a comparison of the three methods was made in terms of energy efficiency and design simplicity. TABLE OP CONTENTS Page INTRODUCTION- --- 1 The Problem- - - - - - - - - - - - - - - - - l The Objective- - - - - - - - - - - - - - - - 2 The Proposed Solution- - - - - - - - - - - - 2 PHYSICAL FACTORS INFLUENCINGGERLIIKATION ----- 4 Seed Structure - - - - - - - - - - - - - - - 4 Germination Techniques - - - - - - - - - - - 9 Germination Factors- - - - - - - - - - - - - 13 Germination Inhibitors - - - - - - - - - - - 16 Viability- - - - - - - - - - - - - - - - - - 18 Dormancy - - - - - - - - - - - - - - - - - - 23 PHYSICAL PROCESSING OF SEED FOR GERMINATION INHIBITION ----- 28 High Frequency Electric Energy - - - - - - - 28 Other Types of Energy- - - - - - - - - - - - 30 A Flan, of Action - - - - - 32 APPLICATION CF HEAT ENERGY- -- ---- - - - ---------------- 35 Investigation Procedures - - - - - - - - - - 37 The Equipment and Its Use- - - - - - - - - - 37 Viability vs. Vitality- - - - - - - - - - - 39 Critical Temperatures- - - - - - - - - - - - 41 Pregerraination vs. Dry Seeds - - - - - - - - 42 Page Germination Vitality Index (GVI)- - - - - - - 42 Time-Temperature Relationship- - - - - - - - -46 Effects of Radicle Projection- - - - - - - - - 5 0 Pre-processing Treatment of Samples- - - - - API LI CATION CF ULTRASONIC ENERGY --- 52 ----60 Investigation Procedures- - - -- - - - - - - 60 The Equipment and Its Use - - - - - - - - - - 61 Effects of Ultrasonic Energy- - - - - - - - - 63 Effects of Radicle Projection - - - - - - - - 64 Problems and Their Solutions- - - - - - - - - 69 APPLICATION OP MECHANICAL ENERGY ---- -73 Nethod of Application- - - - - - - - - - - - - 7 3 The Equipment Used- - - - - - - - - - - - - - 74 The Tests- - - - - - - - - - - - - - - - - - - 8 9 The Results- - - - - - - - - - - - - - - - - - 9 5 cc:.p a r i s c i : op methods- - -- -- -- -- -- -- - 104 APPENDICESI II III IV -108 Assumptions and Calculations of Heat Energy Required for Processing- - - - - - 108 Analysis for Shape of Ejection Head Vane - 110 Comparison Tests -- Unprocessed vs. Processed Plots- - - - - - - - - - - - - 117 Power Used by Semocidometer- - - - - - - - REFERENCES 118 - -119 ILLUSTRATIONS Page Fig. 1- A representative seed in longitudinal section- - - - - - - - - - - - - - - - - - - 5 Fig. 2 - Six common weed seeds - - - - - - - - - - - - 8 Fig. 3- Effect of germination tiir.e upon germination percent- - - - - - - - - - - - - - - - - - - Fig. 4-- Temperature vs. germination for swollen and dry seeds- - - - - - - - - - - - - - - - - - 4C 4 3 Fig. 5 - Photograph of results of water-bath treatment-43 Fig. Fig. - Tine-tenperature relationship for pre­ germinated seeds with non-projecting radicles- - - - - - - - - - - - - - - - - - -47 7- Photograph of the 135 deg. series of treat­ ments plotted in Fig. 6 - - - - - - - - - - - 49 6 Fig. 8 - Effects Fig. 9- Effects of pre-processing treatments upon the GVI--------55 Fig. 10 Fig. 11 of radicle projection upon the GVI- - 51 - Relation between radicle growth and re­ sulting GVI- - - - - - - - - - - - - - - - 57 - Schematic diagram of the ultrasonic test equipment- - - - - - - - - - - - - - - - - 62 Fig. 12 - Cross-section view of the transducer- - - - 62 Fig. 13 - Photograph of the transducer- - - - - - - - 65 Fig. 14 - Application of ultrasonic energy to pregerminated seeds- - - - - - - - - - - - 67 Fig. 15 - Photograph of seeds exposed to an ultrasonic field- - - - - - - - - - - - - - 6 8 Fig. 16 - Soil box used in mechanical energy pro­ cessing experiments- - - - - - - - - - - - 7 5 Page Fig. 17 - Subsurface irrigation equipment used with soil box - - - - - - - - - - - - - - - - - - 77 Fig. 18 - Fine mist sprayer for maintaining surface of soil dust free- - - - - - - - - - - - - - 77 Fig. IS - The Semocidometer used in processing the soil with entrained seeds- - - - - - - - - - 79 Fig. 20 - View of semocidometer showing exit chute and instrument for measuring power input- - 79 Fig. 21 - First design of a percussion head for the semocidometer- - 1 - - - - - - - - - - - - - 81 Fig. 22 - Percussion head especially constructed for experimental modification- - - - - - - - - - 82 Fig. 23 - Ejection head with two vanes- - - - - - - - - 82 Fig. 24 - Percussion head mounted on shaft, with location of soil entrance hole shown in cover- - - - - - - - - - - - - - - - - - - - 84 Fig. 25 - Ejection head mounted on shaft with location of soil entrance hole shown in cover- - - - - 85 Fig. 26 - Method of statically balancing both per­ cussion and ejection heads- - - - - - - - - - 8 7 Fig. 27 - The three vane configurations which were mathematically investigated- - - - - - - - - 90 Fig. 28 - Germination vitality index vs. germination time before processing at 4800 rpm- - - - - 97 Fig. 29 - Germination vitality index vs. germination time before processing at 4000 rpm- - - - - 99 Fig. 30 - Germination vitality index vs. germination time before processing at 3000 rpm- - - - - 100 Fig. 31 - Effect of speed and time upon germination vitality index- - - - - - - - - - - - - - - 102 ■1 INTRODUCTION The Problem Through the years, the growing of sugar beets has always carried a burden that has become synonymous with sugar beet raising, that is, hand labor. Not so many years ago the hand labor extended from the early germination of the beet seed through blocking, thinning, weeding, topping and loading. One by one, agricultural engineering research has shovm methods and equipment suitable for eliminating the hand labor of most of the above mentioned tasks. Mechanical harvesters top and load the beet untouched by human hands. Mechanical blockers in conjunction with precision planting equipment have greatly reduced the need for hand thinning of the beet stand. Seed improvement and processing has also contributed greatly to the precision stand of sugar beets thus reducing the need for blocking and thinning. Improved techniques and cultivating equipment have entirely eliminated any need for weeding between the sugar beet rows. But weed seeds in the row that germinate slightly before or at the time of planting have a head start on the beet seedlings and must be eliminated. expensive hand labor. This still requires 2- Objective The last of the hand labor in sugar beet production could conceivably be eliminated if some method were dis­ covered or developed that would prevent or at least deter the germination and/or initial sprouting of the weed seeds in the soil in the sugar beet rows. It appears that even a temporary delay in weed seed germination and initial growth would allow the beet seedlings to get a head start and more adequately hold their own in competition with the weeds for sunlight, soil moisture and plant nutrients. The Proposed Solution The explicit statement of the objective suggests a plausible solution. It is proposed that a strip of soil, say four inches wide by three quarter inch deep, be lifted up immediately ahead of the sugar beet planter mechanism. This strip of soil would then be processed in some manner so that the germination and/or initial growth of the weed seeds in it were effectively retarded or prevented. The processed layer of soil would then be layed down directly behind the planting mechanism and over the sugar beet seeds. It is generally recognized that few varieties of weed seeds germinate and emerge when germination takes place below three quarters of an inch, so it would be expected that the processed soil strip would be relatively free from weeds for the early growth stage of the sugar beets. -3- There were various .ways in which the soil strip could be processed. In order to determine the possible effective ways of processing the soil strip to prohibit or inhibit weed seed germination, and to have some criteria for evalu­ ating the effectiveness of the processing, it was considered necessary to first investigate the physical factors involved in weed seed germination. It was felt that some property of the seed or some physical factor affecting germination would point the way to the most effective processing technique. In other words, the physical requirements for germination had to be known before realistic steps could be taken to thwart or prevent the germination. PHYSICAL FACTORS INFLUENCING GERMINATION Seed Structure It seems that every seed has at least two basic parts, the embryo and a seed coat* usually does. It may have other parts, and The most inclusive seed is the entire fruit of a plant, Figure 1. This includes the ovary wall (pericarp), placenta which is not always apparent in the matured ovary, and the matured ovule (botanical seed)* Holman and Robbins (26) define a fruit as the matured ovary of a flower. It contains its one or more seeds and such other parts of the flov/er as nay be associated with the matured ovary. In addition to the embryo and the seed coat the matured ovule usually contains an endosperm. This endosperm represents a food reservoir for the embryo to use when germination first starts. Some seeds have an embryo that has developed so far that the endo­ sperm has been used up. In such cases the food reservoir Is in the primary leaves or cotyledons of the embryo. The organs of the embryo are: 1. Shoot - plumule or epicotvle 2. Leaves - cotyledons 3. Grown - hypocotyle 4. Rudimentary root - radicle These organs have a remarkable similarity even between widely differing families and orders. / -5 Endosperm Radicle Plumule Ssedooat Ovary Cavity Cotyledons Pericarp Calyx A representative seed in longitudinal section. This seed, buokeheat, includes the entire Trait. A The first classical study of internal seed morphology seems to have been made by Joseph Gaertner about 1790 De Fruotibus et Semlnibus Plant arum, in two volumes. This work is primarily on fruits, but its excellent presentation of seed morphology appears to have served as the principal source of information on the subject for subsequent botanical publications. Since that time much information has been published about seeds. However many of these sources pro­ vide only fragmentary and, to the writer, unsatisfactory knowledge on seed internals, particuarly weed seeds. Also, the field of embryology seems to be concerned primarily with the early stages of ovule growth rather than the mature ovule, which is an embryo plant. The most comprehensive internal morphological study of weed seeds the writer has discovered is that by Martin (36). He found considerable stability in seed types among slightly related species and genera. "Whereas superficial characteristics of seed such as size, shape, color and surface are myriad and often vary markedly among species or genera in the same family, the significant types of internal arrangement incline to be relatively few and comparatively stable•" He makes a classification of twelve types of seeds according to the size, shape, or position of the embryo. This classi­ fication resulted from a study of 1287 genera of plants, largely from the United States. -7 Some of the weed seeds cataloged and illustrated by Martin were of particular interest to the writer because of their common occurence in sugar beet fields in Michigan. The following six weed seeds were among those illustrated by Martin and drawings were made by the writer after his, Figure 2. Three other pertinent seeds cataloged but not illustrated because no endosperm was discernible in the ovule, are also listed for future reference. Illustrated Seeds 1. Lambsquarter - Chenopodium album 2* Rough Pigweed - Amaranthus retroflexus S. Lady’s Thumb - Polygonum persicaria 4. Barnyard Grass - Echinochloa crus-galli 5. Quack Grass - Agropyron repens 6. Witch Grass - Panicum capillars Not Illustrated (all embryo - no endosperm) 1. Rag Weed - Ambrosia elatior 2. Sow Thistle - Sonchus arvensis 3. Wild Mustard - Brassioa kaber In explanation of Figure 2 it should be said that the drawings consist of combinations of vertical and cross section diagrams of seed contents exclusive of seed coverings. The cross sections represent approximately median cuts. The dark portions represent the embryo and the light the endosperm. ^ I IB Lambs quarter (Chenopodium album) X 20 Rough Pigweed (Amaranthus retroflexus) <3 Lady’s Thumb (Polygenum persioaria) x 2j3 Barnyard Grass (Echinochloa crus-galli) _ X 0 quaok Grass (Agropyron repens) X 10 Wit oh Grass (Panioum oaplllare) Six common weed seeds showing embryo dark, and endosoerm lieht. Germination Techniques Germination of many seeds is no problem. However on other plant varieties the seeds seem to exhibit the very essence of contrariness when one desires to differentiate those seeds that will not grow from those that will. Various techniques have been developed through experience to force germination. The writer is particularly Interested in the means of germinating the seeds of certain weeds common to Michigan sugar beet fields. The weeds selected for special investigation are: 1. Lambsquarter - Ghenopodium album 2. Rough Pigweed - Amaranthus retroflexus 3. Lady’s Thumb - Polygonum persicaria 4. Barnyard Grass - Echinochloa crus-galli 5. Quack Grass - Agropyron re pens 6. “ Witch G&rass - Panicum capillare 7. Ragweed - Ambrosia elatior 8. Sow Thistle - Sonchus arvensis 9. Wild Mustard - Brassica kaber Lambsquarter In his studies to establish definite laboratory methods for the germination of weed seed, Everson (17) recommends the germination be carried out on blotters or quartz sand In petri dishes and that analter­ nating temperature of 20 deg. C. for 16 hours and 30 deg. C. 10- for eight hours be used* germination* nation* He also found that light aids However he obtained only 79 peroent germi­ The other 21 peroent remained as impermeable seeds* Rough Pigweed Using oopper trays equipped with a wick, Thompson (47) has been able to obtain good germination at a constant temperature of 30 deg* C*, without light* Lady*3 Thumb Neither Cross or Pladeck (14) were able to get satisfactory germination under any of the conditions of the experiments* Justice (26), however, found that by chilling the seeds at 2-4 deg. C* in water for 12 to 15 weeks, with subsequent temperature from 18-25 deg* C*, gave good results. Everson found that a temperature alternation of 10-35 deg* C* in extra moist sand for 14 days, followed by an alternation of 20-30 deg* C* gave over 90 percent germi­ nation* Barnyard Grass No information on the germination of these seeds has been found* Quack Grass Shultz (42) has found that 20-30 deg* C* alternation, on blotters produces satisfactory germination. Witch Grass No information has been found on the germi­ nation of witch grass seed* Ragweed No satisfactory method of germinating this species of weed has been encountered in the literature* Heise (24), (25) has tried various combinations of 20-30 deg. C. cycles, with and without light on blotters and sand. Everson tried the following conditions: 1* Constant temperatures of 10, 15, 20, 35, and 40 deg* C. 2* Alternating temperatures of 15-30, 20-30, and 20—35 dog* C* 3* Alternating temperatures of 10-30, 10-35, 3-30, 3-35, -5-30, and -5-35 deg* C* for 1, 2, 3 and 4 weeks before transfer to either a 15-30 deg* or 20-30 deg* C* alternation* None of the above methods gave satisfactory germination* Sow Thistle No information whatever has been encountered on methods of satisfactory germination* Wild Liustard (Brassica kaber) Everson obtained 85 percent germination with 13 percent hard seeds from this species of mustard. The seeds were pre-chilled for five days at 2 to 10 deg* C* before being placed in an alternating temperature of 15-30 deg. C* Either moist blotters or sand was satis­ factory as a substrata. Light was used during the test* Other techniques have been used to force germination in certain instances of hard seed coats. Mechanical scarifi­ cation, hot water treatment, and soaking in concentrated sulphuric acid have been the most common methods used to make hard coats permeable. Of these, the first one is probably safest since it results in less injury to the soft seed present in the lot and is easier to manipulate. In addition, the time period involved in hot water and sulphuric acid -12- treatments varies and must be determined for each species. Barton and Crocker (4) tell of one seed, Scotch broom (Cytisus scoparlus). that can tolerate up to five hours of soaking in concentrated sulphuric acid. They also report the use of liquid nitrogen as a means of making the seed coat permeable. Impermeable seeds of Lielilotus alba were made to absorb water by plunging them in liquid nitrogen (-320 deg. F. ) before placing in water. Four dips of 30 seconds each with one minute between dips was used. If the seeds were also plunged into water at room temperature before and after each dip, the seeds gave 97 percent germi­ nation. Seeds dipped four times without being plunged into water gave 33 percent germination and untreated seeds gave sero germination. Fifteen minutes soaking in liquid nitrogen had no effect on the germination of some species of Imper­ meable seeds. Soaking in ethyl alcohol up to 72 hours has also been used to make certain impermeable seed imbibe v/ater as the first step in germination. Filing through the coat is a common procedure for preparing morning glory seeds for planting. It is believed that nature's way of processing impermeable seeds is the action of soil bacteria and molds working on the seed coat until moisture finally gets through. Of course this may take 2, 5, 10, or 30 years but nature is in no hurry. Germination Factors TOie physical factbrs influencing germination, as found in the literature are:: i 1* Moisture 2• Temperature 3• Light 4. Gaseous exchange 5 • Time In emergence tests of sugar beet seeds Leach, et al (32), conducted controlled ^oil moisture tests at 50 deg. F. and 70 deg. F. The soil moistures were 8.2$, 9.0?5, 10.2# and 13# (dry weight) with 8.8# the permanent wilting percent and 15.8 as the moisture equivalent percent. i In the 70 deg. tests, no germination took place at 8.2 percent soil moisture, but did fairly well at 9.0 percent and gave good germination both at 10.2 and 13 percentj moisture. At 50 deg. F . , in the same soil, there was practically no germination at 8.2 percent, but equally high germination at 9.0 and 13 percent soil moisture. Many other tests reported in the literature could 1 be cited indicating a fairly uniform moisture requirement but considerable variation in the temperature requirement. Light has been shown to implement germination in a number of cases. Weintraub (50), Shuck (43) and Flint (18) all found light beneficial in tlfe germination of lettuce seed but Weintraub and Leggatt (34) both concluded this effect to be only secondary in that certain light frequencies helped break down some of the light-sensitive chemical in the seed coat. -14- Washing in running water.was more effective* Others have re­ ported the use of light in various germination tests with benefit hut the evidence is very inconclusive as to the reasons for light being effective in these cases* Gaseous exchange through the seed coat and between the embryo cells and the atmosphere seems to be a prerequisite for germination* As a matter of fact, there is considerable evidence that gaseous exchange is essential for the continued life of the embryo even while dormant. Respiration studies (4) were undertakin in an attempt to get a definite measure of one of the life activities of the pigweed seed. in moist storage at 68 deg. F. They were held Oxygen absorbed and carbon dioxide given off were measured at intervals during a 901 day period* Rate of respiration showed at least a 10 fold reduction. The beginning of this reduction became apparent after two days and was definite after eight days in moist storage• The manner in which time is an influencing factor is tied in with the physiological structure of the embryo. Freshly matured seeds upon becoming dried enter into a dormancy period. Once dormant they proceed through an after-ripening period. The duration of this period caries from a few weeks to 6-8 months. It is thought that the embryo is undergoing physio­ logical changes that only time can complete before the seed is again susceptible to the germination environment. This will be discussed in more detail in the section on Dormancy. -15- It is perhaps difficult to say which is the most influ­ ential factor in starting the germination process. However the evidence is conclusive that water absorption by the embryo and endosperm must take place before any of the other factors can exert any influence. Of course it is necessary that the moisture pass the seed coat barrier first. During imbibition of water by the embryo and endosperm, a swelling of these structures occurs. If the other conditions for germination are correct, such as temperature and oxygen supply for respi­ ration, the next step in the germination process takes place. This next step is the secretion of enzymes. Starch, fats, and proteins are the principle foods stored in the seed. Naturefs way of making these foods available to the growing parts of the embryo, the radicle and plumule, is by means of a three step process of digestion, transfer and assimilation. The enzymes break down the starches, fats, and proteins into soluble and diffusible substances in the presence of water and oxygen. Due to the concentration gradient between the food reservoir and the growing points, the food solubles flow by diffusion from one living cell to another. At the growing points of the embryo the soluble foods are transformed into cellulose walls and into protoplasm. release of energy. The digestion requires The rate of energy released is dependent upon the moisture available, the temperature of the seed and upon an adequate supply of oxygen. 16 Germination Inhibitors The presence of substances in the seed or seed ooat of several seeds that either inhibit or stimulate germination has been reported. Jhices from fleshy fruits have been known to retard or inhibit the germination of seeds. It is believed that Heinz Oppenheimer in 1922 first postulated the presence of specific inhibitors in fruit juices in addition to the osmotic effect. Tolinan and Stout (48) found that water soluble substances toxic to germinating seeds exist in the pericarp tissue of sugar-beet seed balls and they demonstrated that these can be removed by proper washing. They also tentatively concluded that much of the so-called "Stimulating effects" from liquid seed treatments with inorganic salts or fungicides is actually brought about by removal of toxic substances. They found that water alone was as effective in increasing germination as solutions of various inorganic salts. Hanley and Woodman (22) reported that treatment of sugarbeet seed balls with sulfuric acid leads to an increase in both rate of germination and total germination. They thought the increase due to a greater permeability of the hard seed balls. Garnor and Saunders reported much the same results and conclusions. However, others, V. Stehlik and 5*. Neuwirth of Czechoslovakia, 1927, obtained results that showed this effect to be no greater than that obtained by soaking in 17- running water* Inasmuch as both washing In water and soaking in sulfuric acid result in the removal of toxic substances from the seed coat it is to be expected that both treatments would result in increased germination* Later research of Stout and Tolman (46) indicated that the removal of water soluble nitrogen fractions from the pericarpel tissue seemed to be the real explanation of the beneficial effects of washing or soaking some seeds — radish, onion, lettuce, tomatoe, cantaloupe, and cucumber — tests* prior to germination The enzymatic action associated with germination hydra- lized certain nitrogenous substances producing ammonia* It was this ammonia that inhibited or in many cases killed the embryo growth• Shuck (43) found that repeated germination on the same moist blotters produced gradual reduction in percent germi­ nation of lettuce seeds* In a like manner germination in a shallow layer of water was completely inhibited after 600 seeds had been in contact with the medium* The inhibiting substance was formed most abundantly by seeds immediately after harvest and in smaller amounts or not at all in old seeds. The writer suspects it is a chemical in the seed coat acting as an inhibitor until by liquid or gaseous diffusion its concentration is lowered enough to permit resumption of embryo growth. Barton and Crocker (4) found that germination could be induced by removing the seed coat. Clytie (11) also stated that so called after-ripening of Amaranthus retroflexus is not a matter of the embryo, since embryos of fresh seed - 18- Viability Viable seeds are those that are capable of germinating when placed in the proper environment. It is recognized that it is difficult and not always conclusive to differ­ entiate between viable and dead seeds by means of germi­ nation tests. It seems that vitality of a seed has a meaning different from viability. Vitality is a term signifying degree. bility is absolute - alive or dead. Via­ Hoi,man and Robbins (26) listed five chief factors that determined the vitality of seeds. 1. Vigor of the parent plant. 2. Environment while maturing. 3. Maturity of the seeds. 4. Storage conditions of the seeds. 5. Age of the seeds. Of course, the factors that determine seed vitality will, in their accumulated totality, also determine whether the seed is viable or not. The phases of seed viability con­ sidered in this section will be confined to factors 4 and 5 listed above. Eirst to be considered are the effects of storage conditions on viability. Gane (19) investigated onion, carrot and parsnip seed storage at various percent moistures, temperatures, and U | atmospheres. His results showed that at 0 deg. C. there was no loss or viability in onion, carrot or parsnip seeds even in atmospheres or 70 percent relative humidity. Also there did not appear to be any advantage in reducing the osqrgen content or the atmosphere at this temperature either by keeping the sample tubes sealed or by sealing in nitrogen. At 10 deg. C. (50 deg. F.) onion and parsnip seed showed some deterioration when the relative humidity was 70 percent, and again the results were not errected by the restriction or absence or oxygen. At 20 deg. C. (68 deg. F. ), however, the reduction in viability was considerable, and again the composition or the atmosphere had little erfect, with humidity being the more important ractor. He concluded that storage or carrot, parsnip and onion seed Tor three years was satisractory ir at 60 deg. F. and 50 percent relative humidity. Barton and Crocker (4) conducted extensive investigations at Boyce Thompson Institute on the errect or temperature and moisture content upon the keeping quality or vegetable seeds. They round that the term "air-dried" when applied to moisture content or seeds in storage is misleading. Every type seed tested showed a two-fold percent moisture change during the year when stored open in the laboratory. In further storage tests they found that 23 deg. F. permitted the maintenance of viability for 14 years in all the vegetable seeds included in the study when seeds were - 80- first dried to 6-8 percent moisture. Some of the varieties dropped rapidly in viability during the eight week period immediately following removal to room conditions from 83 deg. P. storage. The greatest deterioration resulted from removing the onion seed. They dropped from 94 to 80 per­ cent germination in three weeks. But when they were only air dried before storing, the germination dropped from 85 percent when removed to 14-29 percent one week after removal. From these data it appears that low temperature is not sufficient to prevent greatly lowered vitality of stored seed. In another series of experiments, the effect of seed moisture on storage at room temperature was studied for dandelion seed over a three year storage period. were sealed in both glass containers and tin cans. The samples Hie glass tubes were not opened from the time of sealing until the germination tests were made, but the tins were opened at intervals of six months for removing samples. The following table shows the results attained by Barton and Crocker (4). Effect of Sealing Dandelion Seeds on Their Germination After Three Years Storage at Room Temperature Seed Moisture in Percent 7.9 6.2 5.0 3.9 Percent Germination Glass Tin 43 60 75 79 0 0 3 61 -21- Thls data seems to Indicate that the harmful effects of opening the seed containers decreased as the moisture present in the seeds at the time of storage was reduoed. The evi­ dence points to the conclusion that low moisture Is more beneficial towards seed vitality in storage than low temper­ ature* Another aspect of seed viability has to do with lon­ gevity in the soil rather than in storage* The seeds of most interest in considering this phase of viability are the numerous varieties of weed seeds which are both a curse and a blessing to agriculture* The longevity of viable seeds in the soil is a matter of considerable interest and wonder to many, including the writer* Darlington’s report on Dr. Beal’s seed vitality experi­ ment (15) stated that 5-6 percent of 1000 seeds germinated after being stored in moist sand 18 inches in the soil 60 years. Toole (49) in his final report on the Duvel buried seed experiment stated that of 107 species buried in 1902, 36 produced some viable plants upon being tested for germi­ nation in 1941 (39 year dormancy). Chepil (9) reported that most weed species contain some seeds that germinate immediately after they are placed under favorable conditions, but that a portion of the remaining seeds lie dormant for various periods. many years. These periods vary from a few months to He further stated that the dormancy period seemed not to be affected by soil texture nor the amount of seasonal rainfall, but is apparently determined at the out-Jj3| set for the great majority of the seeds. The duration of viability appears to be a function of impermeability of the seed coat to some extent. As long as the seed coat is impermeable, there is no chance for imbi­ bition of water and subsequent possible germination. Soil bacteria, molds, fungi, bird,s craws, freezing, and weathering are some of nature’s devices for eroding or changing the seed coat. Thus it may take a few months or many years for a particular seed coat to become permeable. An impermeable seed coat is the best protection possible for maintaining viability. It not only prevents water entering, with the resulting increase in respiration, but also pre­ vents gaseous exchange between the atmosphere and the cells of the endosperm and embryo. One other aspect of viability will be briefly mentioned. Pierpoint (39) reported tests on mechanically injured rye grass seeds (Lollum temulentun)• The seeds were separated according to the type and degree of injury and tested. If less than half the embryo had been destroyed about 30 per­ cent germination resulted while those with more than half the embryo missing showed no germination. Bass (5) also reported that the vitality of a weed seed lowers about in proportion to the percent injury to the embryo. -23 Dormancy The failure of seeds to germinate promptly when pro­ vided with conditions ordinarily suitable for the germination of seed of the species is a phenomenon of rather frequent occurenoe. The reason for this phenomenon is a property of most seeds called dormancy. Barton and Crocker (4) found that most seeds could be forced to bypass the dormancy period if brought directly into the conditions for normal germination from the parent plant upon maturity of the seed. However if the seeds are allowed to even partially dry out they would enter into the dormancy phase and be most difficult to germinate while in that phase. Dormancy of weed seed is a mixed blessing to man. During the years of extreme drought and wind erosion, millions of acres of land were laid completely bare of vegetation during the months of the growing season for several years. Yet the dormant seeds were there and plant growth reappeared quickly after normal moisture conditions returned. With normal growing conditions, the germination and subsequent growth of the dormant seeds of some years past would cover the stricken areas in sufficient amounts to give complete protection again subsequent damaging effects of high winds. This same characteristic of seeds, essential as it is for soil conservation, can bring no end of trouble for the cultivator of the land. Many weeds are serious pests because their seeds exhibit dormancy. Seeds of unknown age keep springing up in cultivated crops despite intensive weed control measures. Seeds exhibiting a high degree of dormancy will be preserved by burial and will germinate only after subsequent cultivation brings them near the surface under the influence of an environment conducive to germination. A number of authorities state that dormant seed will germinate as soon as they reach a physiological state that enables them to germinate, provided that environmental con­ ditions are suitable. To the writer this is circumlocution. The real crux of the problem is what factors operate on the seed to bring it to the said physiologioal state. It is recognized that imbibition of water does not necessarily start the germination process. However impermeable seeds that do not imbibe water readily seem to be especially adapted for long periods of dormancy in moist soils. Atwood (2) found that the respiration rate of dormant imbibed seeds of Avena fatua was very low, suggesting that some factor was at work curtailing cell activity. In the section on germi­ nation inhibitors the writer touched on some possible factors preventing germination, that is, promoting dormancy. Several researchers have come to the conclusion that dormancy is of two distinct types, natural and induced. The writer believes better terms would be internal and environments Internal dormancy would be due to the "drugging" effect of inhibitors in the seed coat, preventing germination until —25 such time as they are leached out, or possibly a physiological unreadiness of the embryo to resume growth* It is worth noting in passing that the writer has found no experimental facts to support the latter possibility — only to the first. all facts point Environmental dormancy would be due to those factors external to the seed, light, heat, oxygen supply, moisture, and so forth, that singularly or In combination v/ould place the seed embryo In an environment unfavorable for resumption of growth. Temperature, moisture and oxygen supply are the all important factors influencing environmental dormancy. Barton and Crocker (4) held pigweed seed (Amaranthus retroflexus) in moist storage for 623 days at 68 deg. 3T. with zero germination. The sample germinated 84 percent within three days after the temperature was raised to 77 degrees. They also found that sealing a moist seed sample in carbon dioxide induced complete dormancy even in ideal temperature ranges and fluctuations. Light has often been mentioned as a factor affecting dormancy. Tfeintraub (50) found the light-sensitivity effect on the germination of lettuce seed to be really caused by action of certain light frequencies in breaking down and in­ activating certain exogenous chemical germination Inhibitors present. These inhibitors may be in the seed coat thus in­ hibiting the initiation of germination, or they may be by­ products of digestion during early stages of germination thus inhibiting the subsequent development of the seedling. Leggatt (33) came to about the same conclusion in his work the effect of blue liprht on the dormancy of lettuce seed. o n vg| JH| 26- An internal factor of some importance is the imperme­ ability of the seed coat* An impermeable seed coat will pre­ vent imbibition of water for months or even years until finally soil bacteria or mold will erode it enough for water to enter* In his work on germination of weed seeds in culti­ vated fields, Chepil (9) found a scattering in time of germi­ nation* This scattering or periodicity of germination was determined for many kinds of seeds and soil types and con­ ditions. There periodicity seemed not to be affected by any of the factors* It appeared inherent in the seed and was largely attributed to variation in seed coat impermeability* Crocker (12) attributes the varying dormancy of seeds in more or less uniform soil conditions to toughness of the seed coat* In the report of the Duvel buried seed experiment, Toole and Brown (49) made a distinction between dormancy in­ duced by a reduction in oxygen supply and that maintained by an impermeable seed coat* Bor example, morning glory (Ipomoea locumora) sprouted within 72 hours after removal from burial for 30 years; while ragweed (Ambrosia trlfida) required six months for the first seedling to show. According to Davis (16) the embryo cycle following ripening is primary or initial dormancy, after-ripening, secondary dormancy, and then germination. Bor the seed Ambrosia trifida, he could force it in and out of dormancy at will by varying the temperature and restricting the oxygen supply* He concluded that the high temperature affected 37- the membrane around the embryo so that it more or less re­ stricted the gaseous exchange in the seed, thus inducing secondary dormancy. The entire problem of the causes of embryo activity and dormancy is complicated by the extreme interaction between the influencing factors. PHYSICAL PROCESSING 07 SEED TOR GERMINATION INHIBITION After having searched the literature for the effect of the determining physical factors upon germination, it next seemed fitting to examine another facet of the problem. The emphasis of the work so far reported was on the vitalizing effect of environmental factors. Seldom if ever were the conditions pushed to the point of preventing germination or of killing the seeds. It is reasonable to suppose that combinations of the physical influencing factors can inhibit as well as promote germination. Search of the literature revealed only a relatively small amount of work directed toward techniques and processes for destroying the viability of weed seed. High Frequency Electric Energy A number of investigators have tested the effect of high frequency waves on seed vitality and viability. HcKinley (35) exposed seeds of Golden Bantam corn to a high frequency current for five minutes. The seeds were killed. At one minute, they were not killed but slightly retarded. And at 30-40 seconds exposure, the early stages of germi­ nation were accelerated. Air-dried seeds were used. Bitten (7) tried various frequencies and exposures on air-dried barley seeds with no significant effects on the germination. ; Siniuk (45) studied seeds tliat were aged and low in germination* With an oscillator tuned to 55 megacycle and a 50 mm plate separation, he found that a two sec* exposure increased the germination of onion, carrot and v/heat seed* Longer exposure resulted in loss of germination as shown: Seed Check Carrot Onion 32 30 Percent Germination 2 sec* 5 sec. 10 sec* 15 sec* 63 82 42 80 36 69 25 52 A number of cereal and weed seed varieties were treated by Lambert, et^ al (31)* They used a 15 megacycle frequency and exposure of 2, 3, 4 and 5 minutes. A two min* exposure reduced the germination of wild mustard from 22 percent to 3 percent, and the germination of quack grass from 88 per­ cent to 9 percent* An effort was made to find experimental results on the effect of high frequency electric currents apart from their heating effect* Apparently internal heating is the major cause of the germination variations reported* In addition, the published reports were meager on the relation of seed moisture content to effectiveness of high frequency electric energy* 30- Other T^rpes of Energy Heat Energy By Conduction It Is well known that seeds have a rather sharp temper­ ature demarcation above which the viability is destroyed, 140-150 deg. P. is considered sufficient for killing most weed seeds as well as insects in the soil. This type of processing was considered to have possibilities and the writer’s investigation of these possibilities is reported in a later section. Ultrasonic Energy Vibrations above the audible are termed ultrasonic. They are mechanical vibrations of the medium and result from a transfer of energy from the transducer to the medium. The effects and limitations of ultrasonic vibration are largely unknown at the present time. Its primary region of appli­ cation has been in liquids because of more efficient transmissibility through that medium. Air makes an excellent insulator for ultrasonic waves, and consequently severely limits its range of application. The meager references on the effect of these waves on seeds were contradictory. The only conclusion the writer made is that there is much still to be determined about the methods and techniques for applying ultrasonic energy. It also was investigated further by the writer, and is reported in a later section. M - 31- Hlgh Current Electric Energy The writer found no evidence that the flow of electric current through seeds has any effect on their germination other than the heating resulting from the electrical reslstanci exhibited by the seed. Light Energy There was no evidence to encourage further investigation of the ability of light to arrest or even delay germination of weed seeds in a time period compatible with a continuous soil processing technique. Ilechanical Energy This seemed to be the most direct method and capable of the most immediate results. It is possible that the soil v/ith its entrained weed seeds could be agitated or beaten severely enough to destroy the seed viability or at least re­ duce the vitality markedly. Weed seeds, and particularly those that have already started to germinate, are susceptible to physical damage. This damage may be in the nature of rupture of the seed coat permitting entrance of fungi and bacteria which reduce the embryo vitality and may lead to early embryo death. Direct damage to the embryo would, of course, speed up the sequence of events leading to lowered vitality or death. The application of mechanical energy has a fundamental advantage over the other methods discussed. In order for the soil processing to be applicable to field equipment it must -32- be a continuous rather than a batoh process. The rate of energy application for effective processing may become very great for some of the methods, particularly the electric and ultrasonic forms. Mechanical energy seemed cheaper per unit of energy, and simpler to apply. It was investigated in some detail and is reported in a later section. A Plan of Action It was the hope of the writer that his search of the literature pertaining to the physical factors influencing germination of weed seeds would point the way, so to speak, to one or several methods of processing the soil in a m a n n er conducive to germination inhibition or total prevention. was only in part true. This Eowever while investigating and plannin the various possible methods of processing the soil and seeds for germination inhibition, the logical basis for a plan of action became apparent. It was as though the pieces of a puzzle had at last begun to fit properly together. The periodicity of dormancy was the key to the puzzle. Two facts reported in the section on dormancy should be re­ called. One — dormant seeds that have wintered over tend to germinate only during a short interval1 of the season. Those not germinating at that time generally remain dormant until that particular season some following year. Two — swelling of the seed is an essential prerequisite to the process of germination but it does not at all assure germi­ -33 nation. In fact, seeds may lay in the ground in a swollen condition for months or years until the temperature cycle and gaseous exchange trigger the growing mechanism. A pertinent question then arose. What, specifically, was the physical condition of the weed seeds that were to be processed? In the writer’s estimation, the answer was arrived at by the process of elimination. Those weed seeds that had not as yet become permeable to moisture and had not swollen would be of no immediate concern because it would be months or years before the impermeable seed coat became erroded away enough for the seed to imbibe moisture and be susceptible to the other factors influencing germination. By this logic, the only pertinent seeds to be processed were those that had already swollen. By similar reasoning, the seeds that were too deep in the soil for the temperature cycle and gaseous exchange to trigger the germination could also be eliminated from consideration in any soil processing techniques, even though they had imbibed moisture. By elimination from con­ sideration of those weed seeds that would not germinate during the germination and early growth period of the sugar beet, the field of the investigation had been considerably restricted; and more important still, an entirely new attitude towards the physical processing of seed for germi­ nation inhibition had been forced upon the writer. -34 It was a new attitude in that the investigation now was concerned only with weed seeds that had already swollen and possibly started to germinate* References in the literature to this restriction of the subject had not been encountered*, Physically and botanically, the swollen seed is very different from the air-dried dormant seed. It was anticipated that it would be much more susceptible and responsive to its physical environment. In fact, It may be said that this is a hypothesis that, if substantiated by experiment, would greatly Increase the effectiveness and simplicity of the various methods for physically processing the seeds for germination Inhibition or complete destruction. All preliminary investigations into the various methods of processing the seeds were made using common mustard (Brassica alba). This was deemed advisable for several reasons First, because of the scarcity of good weed seed samples In large enough quantities for equipment setups and regulation tests. Second, because of its similarity in size and texture to many common weed seeds. Third, for equipment adjustment and regulation, and for time temperature relationships, an easily and uniformly germinating seed was desirable. mustard has these characteristics. Common Germination trials showed 98 percent in 48 hours on hand selected seed. A cooler with temperature of 33 - 36 deg. F. was used to keep the swollen seed ready for the tests. This temperature range Inhibited germination except for a very slow enlargement of the radicle. APPLICATION OP HEAT ENERGY It is well known that high temperatures destroy seed viability. However, information was not available concerning the relationship between temperature and vitality. Also, temperature alone is not enough; the element of time is of the utmost importance in considerations of heat transfer and its accumulative effects. Therefore this phase of the investi­ gation was concerned with the time-temperature relations in the processing of weed seeds with heat and the resulting de­ crease in viability and vitality. The processing of seeds with heat energy has several applications and consequently techniques have been developed for doing this. A common example is the heating of greenhouse soil to kill weed seeds and soil organisms. In this case heating is done at a high temperature, generally with imbedded steam pipes, for a fairly long time to get 100 percent kill. In the case of weed control in beet fields, the goal is not 100 percent kill but rather an optimum retardation, which might be considered the best combination of two factors: one — cost of processing; and two — effectiveness. degree of processing This so-called process efficiency is a major consideration in large operations (field work) as opposed to small operations such as greenhouse beds. Thus, the problem would not be to find a yes or no answer as to what -36- processing will prevent germination but rather to answer the question of how much will do a reasonably good job. Another technique for heat treating seeds that has some application to the problem at hand was the technique origi­ nated by Kleis (4) for treating loose smut in wheat. This was high frequency dielectric heating in Which the internal temperature of the wheat kernel was raised to the point where the smut mycelium in the endosperm were killed but the Wheat germ was not. This required careful control of the internal seed temperature. Thermocouple junctions were placed inside the kernels Which gave him an accurate means of duplicating internal temperatures. However, the actual in­ ternal temperature of adjacent kernels was not known because drilling the holes through the kernels and inserting wires through the holes changed the heat absorption characteristics of the altered kernels so that they would have a rate of temperature rise different from the unaltered kernels. Preliminary heating trials showed it would not be necessary to attempt the measurement of the internal temper­ ature of the seeds since the effect desired was not critical with respect to temperature but rather depended upon both temperature and exposure time. The probable reasons for this effect will be discussed later. Investigation Procedures As stated previously, all preliminary investigations into the various methods of processing the seeds were made using common mustard (Brassica alba). advisable for several reasons. This was deemed First, because of the scarcity of good weed seed samples in large enough quanti­ ties for use in testing setups and other preliminary tests incidental to the controlled tests. Second, because of its similarity in size and texture to many common weed seeds. Third, for equipment adjustment and regulation, and for time-temperature relationships, an easily and uniformly geminating seed was necessary. Common mustard had these characteristics• The hot water-bath method of processing the mustard seeds was selected as the one admitting the fewest uncontrolled variables. Mustard seeds in various stages of imbibition and germination were placed in the water bath for various time intervals. The plan was that the resulting data would then point the way to a method of optimum processing of weed seeds for the most efficient retardation of their germination. The Equipment And Its Use A thermostatically controlled electric oven was used to maintain the water-bath at a constant temperature. However, it was found that during the actual heating of the samples, much better temperature regulation could be obtained by 38- observing a thermometer in the water bath and manually operating the heating coil switch. As is well known, a thermostat switch has two disadvantages: one — it lags be­ hind the temperature - cannot anticipate temperature changes; two — it always permits a temperature variation between limits — the control range. Adjusted for the least range, it still permitted a 2°F. temperature variation. Manual control of the switch during the actual tests, after some practice in getting the wfeelw of the rhythm of the on-off sequence, permitted temperature control with a maximum range of .6°F. Therefore all water-bath temperatures will have this maximum probable error of ^.3°F. The water was in a glass jar in the oven. The ther­ mometer projected above the oven and the reading was visible at all times. An additional aid in the close temperature control was the oven door. It could be partially opened to prevent a too rapid temperature rise. Each sample of mustard seeds consisted of 50 hand selected seeds (for uniformity) which were placed in a fine mesh cloth square, mesh approxi­ mately .8 mm. The corners were brought in and tied forming a small bag with the ends of the tie as a handle for placing the sample in the bath and removing it. Immediately upon removal, each sample was placed in room temperature water for a few moments to insure that any one seed in the sample v/as not favored one way or another because of its location in the bag. -39- Eaoh sample of 50 seeds was then evenly distributed on blotting paper in a petri dish for germination. Germination took place in darkness at room temperature• A number of preliminary tests showed that mustard seeds germinated with remarkable uniformity in this manner. It should be empha­ sised that a reference to treatment of a sample means that a group of 50 hand selected uniform seeds were exposed to the same processing at the same time with no recognizable vari­ ation in processing between individual seeds. Viability vs. Vitality During the initial sample treatments it became more and more evident that the criteria for judging the effectiveness of the treatments would need to be something other than germination. Germination values gave a yes or no answer while what seemed to be really needed was the answer to "how much?". In other words, a particular treatment might permanently stunt the seedlings so they would be of no con­ sequence as far as sugar beet cultivation was concerned but a standard germination test would record the sample as not affected by the treatment. between viability — This basically is the difference having life, and vitality — the degree of potential vigor. One of these early sequence of treatments is shown in Figure 3. All samples in the sequence were soaked for six hours and allowed to germinate to the point of incipient radicle projection —- the seed coat of none was broken by the radicle however. One sample was germinated directly a Swollen Seeds - No Radiole Projection 100 Proeesa Time - 5 minutes Germ, of Control - 96jt # 71-16 Germination, Peroent 80 ' 60 4 Day Gprmination period 40 3 Day Germination Pe riod SO 122 128 134 140 146 Temperature, Degrees Fahrenheit 152 g Effect of germination time upon germination peroent. - 41- a control while the other five samples were water-bath pro­ cessed for five minutes eaoh at the temperatures shown on the chart. The three-day and four-day germination periods were timed from the water-bath treatments and show consider­ ably different values. This posed the problem of what kind of criteria should be used to evaluate the water-bath treat­ ments. This problem is taken up in some detail later but here even the germination percent figures can give some in­ formation concerning the possibilities of heat energy pro­ cessing of weed seeds. Critical Temperatures The curves of Figure 3 where the maximum slopes occur represent the critical temperature range. It can be seen that at temperatures above this range, some of the seeds died during the fourth day. Observations showed that most of the others decreased in vigor also. On the other hand, at temperatures below this critical range, some of the apparently dead seeds showed signs of life on the fourth day, however, they were badly deformed and soon died. The exact magnitude and position of this critical range on the temperature scale should not be examined too critically since it was sub­ sequently found to vary as the degree of germination previous to the water-bath treatment was increased or decreased. -42- Pregermination vs. Dry Seeds If ordinary air-dry seed samples are treated in the wuter-bath, the germination percent is changed very little by the treatment. Figure 4 exemplifies this situation. Four samples were soaked six hours.and pregerminated slightly. Germination was carried to the point of radicle enlargement but not to the point of breakage of the seed coat. Three of these samples were water-bath processed for five minutes each at 132, 135 and 139°F. The fourth was placed in the petri dish directly for germination as a control. Another sample of air-dry seeds were placed in the water-bath for five minutes at 135°F., then germinated along with the other four samples. The resistance of the unswollen seed to such heat energy processing is very pronounced. Figure 5 is a photo­ graph of the samples after four day germination. The control is not included in the photograph, but its appearance was almost identical to that of the dry seeds. Germination Vitality Index (GVI) liention has already been made of the need for a more accurate criteria for defining the effectiveness of the water bath treatments. some time. This problem was a real stumbling block for The literature revealed nothing appropriate. Through observation of numerous germination tests and measure nents of the physical results of sprouting in terms of rate of growth, an arbitrary index of the resulting vitality was -43- 9*t 96< Swollen Seeds- no radlele projection, prooess Time - 5 minutes. # 71-20 Control it 6* °L 132 133 139 Degrees Fahrenheit *lg- * Temperature vs. germination for swollen and for dry seeds. Photograph of results of 5 min. water bath treatment. The germination data is shown in Fig. 4 above. -44- developed. This index was named the Germination Vitality Index, hereafter referred to as the GPVI. These index figures would be arrived at differently for different kinds of seed and the one developed here applies only to the mustard (Brassica alba). Five growth factors are involved in the index. These are the following: 1. The ability of the seedling to free its cotyledons fron the seed coat was found to be a measure of the ability of the seed to recover from the processing shock. A seed of high vitality accomplished this by the splitting of the coat as the cotyledons unfolded. However, others grew out of the seed coat because the hypocotyl was deformed at the crown enough that the coat lodged there while the cotyledons grew away from it as the shoot lengthened. 2. The ability of the cotyledons to unfold was also a requirement for a seed of good vitality. 3. The length of the shoot, that part between the crown and the plumule, was a good measure of the vitality. 4. The length of the root was also a good measure of the vitality. 5. The length of that part of the root containing root hairs indicated its vitality since some treatments produced seedlings without root hairs at all. tested in soil and would not grow. These v/ere -45- The method of arriving at an index value is arbitrary but closely prescribed and subject to very little leeway in judgement. The GfVI criteria may be looked upon as the minimum requirements for a satisfactory level of seed vitality. The procedure used for mustard seeds follows. Calculating the gVI First a germination vitality figure is arrived at for each sample, including the control. Each seed in the sample of 50 seeds is inspected at the end of the third day of germination in petri dishes in terms of the five criteria mentioned previously. These criteria are now stated quant itat ively: 1. Cotyledons must be free of seed coats. 2. Discernible unfolding of the cotyledons. 3. Not less than 10 mm. of shoot. 4. Root hairs extending over not less than 10 mm. of root. Each seed that possessed these four requirements is given a score of one. The total score times two is the germination vitality figure in percent. The GFVI is then obtained by weighing the germination vitality percent numbers of the processed samples on the basis of 100 for the control. As an example, suppose a processed sample had 20 seeds that passed the requirements and the control had 46 that oassed. Then GFVI . 20 X 2 X 100 46 x 2 - 43 ■46“ The significance of this GVI number becomes apparent. If processing the sample has no effect upon the vitality, the GVI of the sample would be 100 plus or minus a small deviation due to the fact that the hand selection of the sample and control was not perfect. If the treatment adversely affected the resulting vitality, ie., lower vitality than the control which was treated just the same except for the water-bath, the GVI would be some value less than 100 and this reduction would be a fair measure of the effective­ ness of the treatment. It can now be seen that a GVI value about 100 would mean that the treatment in effect improved the vigor of the resulting seedlings. This actually occured a number of times as subsequent data will show. A most important result from the use of the GVI values is that it is now possible to compare different groups of samples not handled alike previous and subsequent to the heat treatment. Since it is based upon a relation of the treated sample to the control, it is to a large measure independent of all the random factors affecting germination. Time-Temperature Relationship Information that is more precise can now be obtained with the aid of the GVI rating, for the various water-bath treatments. The results of six series of water-bath treat­ ments showing this relationship are plotted in Figure 6. The seeds used in these series of treatments were soaked and partially pregerminated but with non-protruding radicles. H — o ISO* #61-31 — o 14if #81-17 — « 138* #•1-13 - - - •130" #91-13 --- x 185* #61-27 — A 120* #81-31 i i 1 2 Processing Tins/ Minutes Time-tenperature relationship for pregerminated seeds with non-protruding radicles* a -48" Figure 7 shows the 135°F* series of samples as they appeared Just prior to the GFVX determination* A few words should be said about the stunting of the seeds. There are very large differences in the abilities of seeds within the same sample to recover from the processing shock. For example, the 1.5 min. sample in Figure 7 shows some seeds that germinated as vigorously as any in the control (upper left sample)* Others had extremely long radicle projections, without root hairs, however, but could not free themselves from their seed coats. Still others had good cotyledon development but the radicle stopped grov;ing after merely breaking through the seed coat. Higher temperatures and shorter treatment times tended to produce cotyledon development with no shoot length and very short, less than 1 mm*, radicle projection; while lower temper­ atures and longer treatment times tended towards long thread like radicle projections, with very few root hairs, and cotyledons still encased in their seed coats* The curves of Figure 6 can be used as the basis for determining the time required at a given temperature to pro duce any given percent reduction in vitality of the seeds. However, it should be realized that these data apply only to seeds In which the enzymatic activity preliminary to germination has already begun, and in which a radicle en­ largement has already occured but without as yet breaking the seed coat. -49 Fig. 7 — Photograph of the 135°F. series of treatments which are plotted in Fig. 6* 50- Effect of Radicle Projection Ike question now arises whether the GVI picture will be altered if the radicle has actually broken through the seed coat at the time of processing in the water-bath. Data was obtained that proves that the picture is greatly altered* First, the manner in which the picture is altered will be explained; then some of the reasons for the change will be presented and checked against the experimental facts. Figure 8 gives the results of the first phase of this investigation into the problem of radicle projection vs. GVI for a specified water-bath treatment. Four series of samples v/ere prepared by soaking six hours and then placed in petri dishes for the starter germination. Two series were water- bath treated Just prior to the projection of the radicles through the seed coats. One series was treated at 180°F. v/hile the other was treated at 150°F. The samples of these two series were treated for various lengths of time as shown in Figure 8. The last two series were continued in the gerninator until the radicles protruded 1 to 4 mm. beyond the seed coat opening; then they were treated for time lengths the same as the samples of the seeds with non­ protruding radicles. The reduction in GVI with increase in radicle pro­ jection was large enough to have a great deal of influence on the subsequent thinking and planning of this project. To Dry Seeds at 125°F.F. n ;A 120 Index (GVI) Dry Seeds at 120*F. -Q 150° 0- -0 150° # 01-31 X- -X 120° d- 120° 100 f § 81-31 81-31 81-31 80 ■120°F. - No Radicle Projection \ Vitality / 0- V \ 60 \ i U! H I V Germination \ \ 40 v \ /-1D0 F. - Ho radicle Projection 20 ^jldu a 150°F. \ 0 6s. 6s. - 1-4 mm. X\ Rac Radicle Projection - 15s. ^ \ 120° F. - 1-4 mm. Rtidiole Projection x~~ s. 30s. lm. 2m. 5m. Processing Time, Seconds and Minutes 10m. n&.8 Effects of radicle projection upon the germination vitality index. 20m. - 52- still further acoentuate the importance of th.ese results two other treated samples are shown on the same graph* These are the two points representing samples of air-dry seed water-bath treated directly without previous soaking or initial germination* Note that in both cases the water-bath treatments actually improved the germinating quality of the sample seeds* The difference in GVI between the two dry seed samples was too small to have any significance, but the spread between the three GVI values at 120° for five min* was of great significance and proved to be of great potential value in working out the latter phases of this project. Pre-processing Treatment of Samples As a result of the large differences just noted, it was deemed necessary to investigate in greater detail the vari­ ables that were determining these results* The variables are the following; 1* Imbibition of water prior to processing — this factor was discussed at some length in a previous section* Suffice to say how that a seed is highly impervious to its physical environment while it is in an unswollen state* How quickly this physiological unresponsiveness deteriorates after imbibition takes place is not exactly known. 2. Start of enzymatic activity — with an increase the water content of the seed, the cell hydration increases, thus activating the enzymes• additional enzymes* -t-vick +->10 Zymogens are converted to As the cell hydration progresses througl||||| ftnorvmia«=; HTft t-ransDorted into the tissue - 53- where the stored plant food is located, converting the starches, oils, and proteins into the new tissue walls of the radicle and the stem* The starting of this process occurs within hours after the initial hydration of the embryo cells# Meyer and Anderson (37) state that the rate at which the enzymatic reaction will proceed is influenced not only by the temper­ ature, but also by the length of time which the reacting mixture of enzymes and substrates have already been at that temperature. They also state that enzymes are inactivated or destroyed at temperatures considerably below the boiling point of water. They further state that attemperatures around 50°C# (122°F#), most enzymes in a liquid medium are inactivated; while most enzymes in a liquid medium are completely des­ troyed at temperatures between 60 and 70°C# (140 and 158°3P. ), and that this destruction is in all probability a heat coagulation phenomenon. 3. New cell structure — a non-projecting radicle is, in general, just an enlargement of the embryo radicle with much the same cell structure, but as it projects from the seed coat it has a growing tip with meristematic tissue which is very thin in the cell walls and consequently highly sus­ ceptible to heat injury but no information has been found in the literature concerning this point. 4. Dilution of inhibitors — this point was also investigated at some length in a previous section. In summary, there are certain substances in the seed coat that act as inhibitors of the germination process. Some authorities believe they inhibit enzyme activity; while others believe they increase the impermeability of the seed coat, thus pre­ venting gaseous exchange between the atmosphere and the embryo* Numerous tests on mustard seeds by the writer have given convincing proof that a six hour soaking period previous to other treatments and processes increases its over­ all GVI but especially reduces the spread in GVI between seeds in a sample of common run seeds (not hand picked). As ex­ plained in a previous section, this is due to an extreme variation in permeability of seeds which can be largely equalized by reducing the concentration of the inhibitor. These four factors constitute the difference between the seeds in their air-dry condition and condition as pro­ cessed when having a slight radicle projection. The effect upon GVI of these factors is further illustrated in Figure 9. It does not give a very clear picture of the effect of each factor since it has been so far impossible to isolate these factors and study their effects one at a time. Another example of the interrelationship between these factors is that betv/een enzymatic activity and radicle growth. They cannot occur except at the same tine. If new cell formation ceases, the concentration of soluble food materials builds up thus temporarily inactivating the enzymes. Meyer and Anderson (37) state that a build up in concentration of -55- termination Vitality Index (OTI) 100 100 95 94 D B 65 60 60 40 SO A B C A - 1, Soaked 6 hrs. at room temp. 2, Stored at 34TF. for 8 days. 3, Radlole projection 1-2 mm. B - 1, Soaked 6 hr8. at room temp. 2, Stored at 34°F. for 8 days. 3, Ho radlole projection. 0 • If Soaked 6 hr8. at room temp. 2, Prooeased Immediately. D - 1 9 Soaked 1/2 hrs. at room temp. 2, Processed immediately. B - 1, Air-dried sample. 2, Processed immediately. All fire samples processed one minute at 130*F. Fig. 9 Effoots of pre-processing treatments upon the germination vitality index. the end products of enzymatic activity is a powerful inhibitor to that activity* Also it is obvious that new cell formation can not continue without a constant replenishment of soluble plant food materials which can come, in the seed, only from enzyme activity* In Figure 10, there is another demonstration of the re­ lation between these factors and the resulting GVI drop for processing at 140°F* for one-half min* Here, however, length of radicle projection was taken as a measure, or index, of the combined effect of these factors* The seeds for the two series of treatments v/ere hand selected, then divided into two equal parts* Series one was soaked for six hours, then each individual sample of 50 seeds was placed in a petri dish for the initial germination. The second series was placed in petri dishes for initial germination without the six hour soaking, and as near as possible at the same time as the samples of series one. Zero time on the chart corresponds to the time at which all the samples were placed in petri dishes for the initial germination. At zero time a sample of each series was processed in the water-bath, then returned to the petri dishes for completion of the GVI determination. At each succeeding three hour interval for a total of 18 hours, another sample of each series was processed. The average length of radicle figures were found just prior to processing in the water bath. Relation Between Radlole Orowtli and GVI Prooestlng Time 1/2 llln« Prooeealng Temperature 140°P. # 91-17 I o> I % 7 N * 6 9 12 15 Germination Time Before Prooesslng, Houre fi&* 10 - Relation between radlole growth and resulting GVI drop a fof* n m « « a * 4 i i a a^ 1 AfP « . . . L.i a _ a ____a . - Several Interesting and pertinent facts show up on these curves. The most obvious fact is that pre-soaking made the seeds very susceptible to heat injury, even when the processing v/as done long before the radicle broke through the seed coat. This increase in susceptibility was of about the same magni­ tude throughout the entire range of time studied. The next fact worth noting is that the average radicle projection was always greater on the pre-soaked samples• At this time only conjectures can be made as to the reasons for these results; however, as a matter of fact, knowledge of the reasons is not necessary for the use of these facts in the processing of the soil and the beet seeds for better weed control. The longer radicle projections of the pre-soaked samples are undoubtedly due to the elimination of the inhibitors, thus starting respiration sooner in the embryo, followed by new cell growth in the radicle. The reasons are not so clear for the reduction in GJVI of the presoaked samples compared to the unsoaked ones. The writer partly attributes it to the fact that more zymogens have been converted to enzymes, thus causing a greater susceptibility to permanent enzyme inactivation in the pre-soaked seeds. If the right half of the curve only were considered, it would be very logical to assume that the reduction in GfVI of the pre-soaked compared to the unsoaked was due to the longer radicle projection and its greater susceptibility to heat injury, but the left half of the curves prove that some other 59- factor is involved* Lastly, the writer has no explanation for the increase in GVI of both series of samples during the first three hours of germination* Apparently some other factor or factors as yet unknown and unsuspected are also in­ volved* In summary, these heat energy data and results are the basis upon which estimations could reasonably be made as to the amount of heating required for a soil strip to reduce the germination vitality of the entrained seeds by a given amount. The important factor in such a method of physical processing would be the amount of heat required. Appendix I gives the assumptions on which these calculations were based, as vrell as the complete calculations • The answer obtained was approximately 55 BTU per foot of row when processing a strip four inches wide by three-quarters of an inch deep. This heat requirement when translated in terms of gallons of fuel oil per hour for a four-row planter operating at two miles per hour would be roughly 15 gallons per hour. APPLICATION OF ULTRASONIC ENERGY Mechanical vibrations above the pitch of the human ear are termed ultrasonic vibrations. They, like sound waves, result from a transfer of energy from a transducer to a medium. Air is an even poorer medium (less efficient) for ultrasonic energy than for audible sound energy. This efficiency drops off as the frequency increases. However, the power efficiency increases as the frequency increases (6). Investigation Procedures With these facts in mind, it was decided that water should be the transfer medium and about five megacycles should be the frequency used. Some method then had to be developed for holding the seed samples in the ultrasonic field for the required exposure time. Also some method of obtaining a known, or at least a constant strength field was necessary. It was planned that, instead of having a time-temperature re­ lationship as was had for the hot water bath process, there would be a time-intensity relationship. It was thought there need be no investigation of the heating effect of the ultrasonic waves since if heating of the seed was all that was accomplished, the heating could be done much easier and less expensively by other means. From the search of the literature, especially Bergmann (6), Carlin (8) and White (51), it was found that the early Investigators suspected that much of the detrimental effect of ultrasonic energy upon living matter was due to coagulation of colloidal material in the cells. Therefore the plan was to hold the medium (water) temperature fairly constant and near the normal room temperature so that whatever effects were evident could not be attributed to the resulting waterbath temperature. They could then be attributed probably to internal insensible heating or to mechanical coagulation of protein colloids in the seed cells. The Equipment and Its Use Figure 11 is a diagram of the equipment as used for this investigation. The oscillator was a 50 watt crystal con­ trolled oscillator similar to amature and commercial trans­ mitters. The inductance coupling was for the purpose of matching the impedance of the oscillator to that of the trans­ ducer. The R.F. ammeter, in conjunction with the plate volt­ meter on the oscillator permitted the adjustment for resonance and maximum current through the transducer. Figure 12 is a cross-section of the transducer showing Its construction. The sound field traveled upward from the one-half inch diameter barium titanate crystal and, according to the makers of the crystals, diverged at about a five de­ gree angle. It was found after considerable experimentation that a glass tube with 13 mm. l.D. located over the hole with a piloted flange did a fair job of constraining the seed samnle in the ultrasonic energy field. *** It was further found .jy 62- Inductance coup! ing ter tank £ High frequency oscillator R.F. ammeter 7 Fig. 11—— Schematic diagram of the ultrasonic test equipment used in the processing of the mustard seed. Air vent r.luas tube Locating collar \ Water insulated lead-in wire V * * *m '* x Sealing material ////////////// Fig. 12 — Cross—section view of the transducer. A that the field intensity created an upward pressure which caused the seeds to circulate up in the center, down along the tube surface, and then in to the center and up again* Under the usual operating conditions, to be listed later, this circulation cycle took about three and one—third seconds* Effects of Ultrasonic Energy The first of these tests were made before the conception and development of the Germination Vitality Index; so that the data was obtained in terms of ordinary germination figures The first tests were at 4,500 Kc with 2*8 amperes through the transducer* The seeds had been soaked for six hours just previous to the processing without initial germi­ nation* The 30 minute exposure to the sound energy pro­ duced zero germination with only 1 out of 100 seeds showing any sign of germination subsequent to the processing. Both the 10 minute and the control, which had no processing, germinated 98 percent. These first tests were made without placing the transducer in a water bath, so that the only water used was that in the glass tube. Consequently the temperature rose during the tests to an ambient temperature of 114°r. In order to eliminate the sensible heat factor, the control was also placed in a 114°F* water—bath for 30 minutes. So the lethal effect of the 30 minute exposure to an ultrasonic field could not be charged only to the rise in temperature. However, it is possible that the Internal heating due to the field was enough that in conjunction with -64- the sensible heat it caused permanent enzyme destruction, Figure 13 is a photograph of the transducer as used for these first tests. The glass tube was sealed to the brass shell with liquid solder and a rubber gromnet. The water temperature rise was undesirable so that sub­ sequent tests were made with the transducer in a metal tank, I'etal was necessary so that the water could be grounded. Other­ wise hand capacitance while working around the transducer caused large current variation due to detuning. The air vent for the transducer was found desirable not only to empty any leakage water but also to eliminate a lowered pressure in the shell which often broke the bond between the crystal and the shell top. Seemingly alike crystals varied greatly in the intensity of the field produced. This was true to such an e::tent that the amperes through the transducer gave no real indication of the intensity. The simplest indicator was the height of the fountain when the glass tube was removed. Host of the tests were carried out with an intensity that would produce a 1/4 to 3/8 inch fountain in water four inches deep. Effects of Radicle Projection A great deal of trouble was had with leakage from the water tank into the shell of the transducer. This water would change the resistance and capacitance to such an extent that it was impossible to keep the correct impedance match. Changing to a different type of glue and installing an air Pig. 13 — Photograph of the transducer as used in the first tests. The glass tube was sealed to the shell and water placed in the tube. -66• vent eliminated this problem. Further trouble was had in main taining a low resistance contact between the under surface of the shell top and the upper silver plated surface of the crystal. The glue did hot maintain a constant pressure of the crystal against the shell. After this difficulty was tracked down, the solution was simple. A fine spring-brass length of wire slightly longer than the diameter of the hole in the shell was sprung into the hole so that a constant pressure electrical contact was formed between the crystal surface and the shell. After these, and a number of other minor problems, were solved so that the field intensity could be kept constant for hours at a time and could be quantitatively reproduced at will, then some controlled tests on the effects of radicle rrojection upon the ultrasonic processing were made. Figures 14 and 15 show the effect of varying the processing time on progerminated seeds in which the radicles were projecting £ to 2 mm. on all seeds used. the water in the tube was 87°F. The ambient temperature of The current was 1.55 amperes, and the free fountain height was 5/16 inch. The actual power leaving the upper side of the crystal was estimated to be seven watts. The frequency was 4.97 me. were in each sample. As usual, 50 seeds The water height in the tank was ad­ justed so that a volume of 10 cc. of water was in the tube at the start of the tests. During the tests the radiation nressure caused the water to rise in the tube about 2 mm. above that in the tank. 67- Radicle Projection *5-2 BUB. Frequency 100 # 10C 4.97 m.c 121-3 96 & 80 H •S a 22 60 4> g 60 I S 80 10 0 10 20 SO Exposure Time, Minutes • Fig. 14 Application of ultrasonic energy to mustard seeds which were pregerminated to a radicle projection of 0.5 to 2 mm. A -68 F ig.-15 — Photograph of seed samples just prior to GVT determination. These seeds were exposed to an ultrasonic field and then germinated for 3 days. The GVI data for these is shown in Fig. 12. 69 The ultrasonic radiation appeared to have considerably more effect on the radicles than on the cotyledons* Most of the seeds, even of the 30 minute exposure sample, had cotyledon development after the processing* The characteristic be­ havior was for the cotyledons to split the seed coat and un­ fold while the radicle having elongated only a fraction of a mm. would produce a very few small root hairs and a flat stumpy tip. The cotyledons, instead of getting green as they unfolded became reddish or mottled lavender mixed with green* Problems and Their Solutions The problems encountered in the application of ultra­ sonic energy to the germinating mustard seeds can be classi­ fied under four headings: The high frequency oscillator used to activate the transducer was a 50 watt 5 megacycle oscillator* Due to the losses in the electrical equipment and the low efficiency of the transducer it was estimated that about seven watts were actually being radiated into the space where the seed samples were. This small power required that the exposure tine be considerably extended. Exposure times of ten to twenty minutes were entirely too long for the acquisition of useful data for the problem at hand. The second major problem was the transient variations in the transducer efficiency* The transducer was a barium titanate crystal glued to the under side of a brass plate with the electrical connections made to the under side of the crystal and to the brass plate. J It was necessary to have a water tight seal between the Jj| 70~ crystal and the brass plate, and also necessary to allow the crystal freedom for vibration* These two requirements were antagonistic and caused considerable delay and experimentation in the application of ultrasonics to the problem at hand. The third major problem was the unknown internal heat in the mustard seed. An investigation of the literature showed that at least two possible effects of ultrasonic energy on living tissue could be expected. One was an internal heating due to molecular acceleration of the tissue and the other was coagulation and precipitation of protoplasm. It was known that heating of the mustard seeds would reduce the germination and vitality but no feasible means was found of separating the internal or insensible heat factor from other causes of vitality reduction. The fourth problem was the unknown ex­ posure time of the seeds. The seeds were circulating in a v:ater bath in the ultrasonic field and consequently would be exposed to the field only occasionally. The first problem could be easily solved, but the ex­ pense of larger equipment did not seem Justified until solutions of the other three problems were obtained. The second problem of variations in transducer efficiency -«ras solved by redesigning the brass cartridge and devising a new method of attaching the crystal to the brass plate so that it would be free, but still be in electrical contact. The problem of the unknown exposure time was solved by re­ 71- straining the seeds to a definite position in the ultrasonic field. This was accomplished by partially imbedding the seeds in some special red wax and this was suspended in the center of the ultrasonic beam. The partial solution of the last problem, the Insensible heat factor, determined the fate of the ultrasonic energy method of processing weed seeds. During numerous experiments with the ultrasonic transducer it was found that a given exposure of the seeds in conjunction with an appreciable sensible heat rise of the water caused drastic germination vitality reduction. It seemed quite logical to suppose that there was considerable insensible heat that could not be directly measured and this was actually what was largely responsible for the positive results of ultrasonic radiation. In the experiment wherein the seeds were partially imbedded in the wax it was subsequently found that the central portion of the wax became quite soft, even when the wax in the ultrasonic field was surrounded by water. This hint formed the basis for a number of subsequent ex­ periments with given sized wax pellets in the ultrasonic field in which the softness of the wax after a given exposure time was compared to the softness acquired as a result of specified heating. The conclusions were unmistakable. On the assumption that the internal parts of the seed would absorb the ultrasonic energy in much the same manner as the wax absorbed the energy, it was concluded that the reduction in germination of the seeds exposed to an ultrasonic field -72- was brought about largely by internal heating of the seeds, rather than by other effects of the field, nevertheless the data seems to show clearly that ultrasonic radiation, even with the very small power used, produced considerable re­ tarding effects other than heating on the pregerminated seeds. It seems improbable that enzyme inactivation was the major result of the radiation since the cotyledons developed quite well. However, practically no new tissue, either in the stem or radicle, was formed which leads the writer to suspect that the radiation adversely affected the transport system by which the products of enzyme activity are transported to the areas of new growth. A more plausible hypothesis is that the radiation changed the nuclei of the cells so that they were no longer capable of division. Suffice it to say here that the sequence of physiological events leading up to the end result described are not known and present a number of challenging problems for further research. Sorting out the effects other than heating from the application of ultrasonic energy to the seeds called for a background of knowledge and experience in plant physiology that the writer lacked and therefore this phase of the problem was left at this point so that time would be available for a more detailed study of the remaining method — cation of mechanical energy. appli­ -73- APPLICATION 07 MECHANICAL ENERGY Method of Application While investigating and planning the various possible methods of processing the soil and seeds for germination in­ hibition two facts became apparent and took on great signifi­ cance in determining the logical method to follow in regard to the application of meohanical energy. (1) These facts are: Dormant seeds that have wintered over tend to germinate only during a short interval of the season. Those not germinating at that time generally remain dormant until that particular season some following year. (2) Swelling of the seed is an essential pre­ requisite to the process of germination but it does not at all assure germination. In fact, seeds may lie in the ground in a swollen condition for months or years until the temperature cycle and the gaseous ex­ change trigger the growing mechanism. It seeraed logical to deduce that those weed seeds which had not as yet become permeable to moisture and had not 37/olien would be of no immediate concern because it would be months or years before the Impermeable seed coat became eroded away enough for the seed to imbibe moisture and to be -74- susceptible to the other factors influencing germination. By further reasoning the conclusion was reached that the only pertinent seeds to be processed would be those that had al­ ready swollen. It was also reasoned that the seeds that are too deep in the soil for the temperature cycle and gaseous exchange to trigger the germination could also be eliminated from consideration in any soil processing technique even though they had imbibed moisture. Thus in the investigations of the application of meohanical energy it was decided that only those weed seeds that had already shown some evidence of germination would be considered in evaluating the results of the mechanical energy processing. The procedure chosen to evaluate the applicability of mechanical energy processing of the soil with entrained seeds is as follows: Soil samples containing weed seeds in various stages of incipient germination would be processed through some sort of an instrument by which the weed seeds would be reduced in vitality. The quantitative measure of this reduction in vitality would be by means of the Germination Vitality Index which was developed and reported in a previous section. The Equipment Used In order to have soil samples of uniform soil type, moisture content, and tilth it was necessary to have a re­ serve. The soil box usedjEigure 15,measured eight feet long, Fig* 16 - Soil box used in mechanical energy processing experiments • three feet wide and one foot high. It was placed in a room that had thermostatic control of the temperature to reduce one of the variables in seed germination. The soil for the box was obtained from a field that had been in sugar beets for the greater part of the past six years. The soil was considered to be fairly typical of much of the sugar beet fields in this part of the state in that it And •.;as rather low in organic matter^puddled quite easily. Due to its inclination to puddle when wetted, the soil proved to be difficult to condition and maintain in uniform condition for the processing and germination experiments. It was early found that watering the soil by a bucket or can would puddle it and consequently crust the soil so that no seeds would come through the crust. Special equipment and techniques were developed for irrigating this soil. The equipment shown in Figure 17 was used for the subsurface Irrigation of this soil. A sharpened probe had a number of small radial holes so that irrigation was effected at various levels from the bottom of the soil box to three inches from the surface. It was then found that some means was necessary to prevent the top surface from drying out. This was accomplished by means of a sprayer as shown in Figure 18. The surface of the soil box was sprayed lightly with this fine mist sprayer twice a day during the time of the experiment. This spraying serves two purposes. One was to keep the surface of the soil moist so that any weed seeds very near the surface would have a chance to germi- Fig. 17 - Subsurface irrigation equipment used with soil box. nate. The other purpose was to keep down the dust while the soil was being processed. Cultivation of the soil box was found to be no problem and, consequently, an ordinary garden rake was the only instrument used* An instrument for the actual meohanioal energy pro­ cessing of the seed next had to be constructed. This instru­ ment, subsequently referred to as a semocidometer (literally an instrument for killing seeds), is shown in Figure 19. It consisted of an electric motor with a built-in variable speed drive, suitable V-belt and pulleys, and a vertical shaft on which was attached a head for transmitting the mechanical energy directly to the soil. TOie soil with entrained seeds entered the hopper on top of the box where it fell down onto the rotating head* After receiving the mechanical energy it dropped on down to a reservoir below the rotating head, where it could be taken out when necessary into a box and taken bad: to the soil box. The motor, variable speed drive, and pulley arrangement was such that the rotating head had a speed adjustment of 1000 to 4600 rpm* Suitable meters were attached in the lines feeding the motor so that the power in­ put under various conditions could be recorded. Figure 20 is a view of this semocidometer from the opposite side showing in more detail the exit chute for the processed soil, and also showing the instruments used. m The design of the rotating head presented difficulties which were largely overcome as the results of several false starts, a mathematical analysis of the most efficient vane design, and numerous experiments evaluating the impact actions of the head parts. An obvious first design con­ sisted of the welded-up head shown in Figure 21. It was made to simulate the action of a hammer-mi11 grinder by having the soil drop down on the rotating bars near the outer edge. All partially germinated weed seedlings were not killed by this treatment, even with head speeds of 4800 rpm. Re­ duction of the germination vitality index by 10 to 20 points was often times possible but was not considered satisfactory. After some analysis of the problems involved in imparting mechanical energy to the soil two main types of heads were decided upon for construction and trial. These heads were Urnown as the ejection head and the percussion head. The two heads corresponded to the two possible types of action between the soil and the head. The soil can be dropped down near the outer edge of the rotating bars where the bars will strike the soil pulverizing it and possibly damaging the entrained weed seed. It is also possible to drop the soil at the center of rotating vanes so that the soil is thrown out at a high velocity against a circular plate. The first tyne is known as the percussion method and the second type, the ejection method, hence the names of the two types of heads. These two types of heads are shown in Figure 22 and Figure 23. -82- Fig. <22 - Percussion head especially constructed for experimental modification. Fig. 23 - Ejection head with two vanes. - 83 - The two methods of Imparting mechanical energy to the soil required different locations for the entrance of the soil to the rotating head. Figure 24 shows the percussion head mounted on the vertical shaft and the hopper with the location of the entrance hole. The circular steel plate around the outside had a diameter of 1 inches with about 3/8 of an inch clearance between the plate and the outer edge of the rotating bars. The entrance hole for the soil was two inches from the outside edge of the bars. In Figure 25 the ejection head is shown mounted in the cage with the soil hopper dis­ placed to show its construction and relation to the head. Both of these heads appeared to have merit with the ejection head produoting considerably larger reduction in the GFVI. f As mentioned previously, the first preoussion head con­ structed was that shown in Figure 21. In this head the four bars were welded directly to the quarter-inch circular plate. It v/ill be noted that opposite bars were welded to the same side of the plate. This was necessary to satisfy the con­ ditions for dynamic balance. However, it was soon found that this welded construction did not permit changes and modifi­ cations contemplated to effect improvement in performance. So this head was soon discarded for the one shown In Figure 22. It has eight bars bolted together with four bolts. has a flange between the two square plates. The hub Spacers are placed betv/een the bars of such a thiclaiess that the nuts and bolts will draw the square plates tight against the hub 84 - Fig* 24 - Percussion liead mounted on shaft, with location of soil entrance hole shown in cover* -85- Fig. 25 '- Ejection head mounted on shaft with location of soil entrance hole shown in cover. m -86- flange. This permitted considerable versatility in the place­ ment of the bars and the number of bars used. However, again, it was found to be absolutely essential that the bars be placed directly opposite from each other to satisfy the con­ ditions for dynamic balance. It was realized, of course, that dynamic balance could be obtained by the addition of weights, or by drilling out the bars for any given arrange­ ment. To obtain dynamic balance by this method is most laborious so it was found expeditious to arbitrarily place the bars opposite each other so as to more or less automatically take care of the dynamic balance of the system. Subsequent tests showed that any number of bars less than the eight, gave very poor reduction In GfVI. m m of Static balance of the percussion head was obtained by varying the number of spacers under the four nuts holding the head together. Figure 26 illustrates the system used in obtaining the ma-sMrmim degree of static balance. A shaft without the head on it was slowly rolled back and forth on the two ways while their level was varied. "When the same freedom of movement was observed in either direction the ways were assumed level. The head was then fastened to the shaft and the head and shaft given a very slight torque and then left to seek its equilibrium position. The bottom of this position was marked with a piece of chalk and the same process of the slight torque and an equilibrium position was repeated again and again. The side of the head where the maximum number of chalk marks appeared -87 t£ «r ' Fig._ 26 - Method of statically balancing both percussion and ejection heads. —88 was considered the heavy side and either spacers taken out of that side or spaoers added to the opposite side* TSiis method of statio balancing proved extremely accurate as shown by the fact that a spacer of three grams removed from under one of the nuts would rotate the cluster of chalk marks 180 degrees. In connection with the relation of statio balance to dynamic balance, it was found that even though this head v/as in static balance as accurately as could be obtained by the above mentioned method, if the heads were not placed in pairs directly opposite from each other, extreme vibration due to unbalance appeared at about 3500 rpm. At 4000 rpm the vibration became severe enough to make the whole instrument move across the floor. By satisfying the conditions for dynamic balance and with the same degree of static balance the entire instrument could operate at 3500 rpm* without shaking off a penny laid on the frame of the machine. The ejection head, likewise, had to be statically balanced. How­ ever, its dynamic balance was satisfactory because of the design of the head* Several possibilities in regard to the location of the vanes on the plate became apparent when the design of the ejection head was considered. It was realized that the soil particles coming down on the center of the head would acquire a final velocity that would be some function of the shape of the vane and its relation to the axis of rotation. In order to save the time required to construct and test a variety of -89- heads, a mathematical analysis of the velocity of the soil as a function of the shape and position of the vane was under­ taken* It soon became apparent that a general solution in terms of the vane shape became extremely involved* In lieu of a general solution, it was considered expedient to obtain particular solutions for the three vane configurations that would permit simple solution of the equations involved. The three vane configurations investigated are shown in Figure 27. Appendix II gives the solutions for these three cases, and it was these solutions that were the basis for selecting the non-radial straight vane as the one to be constructed. The Tests The first test was started immediately upon bringing the soil in from the beet field and placing it in the test box in the building. The soil was smoothed and watered down. The south half of the box was divided into two plots. No. 1 was left as isexcept for occasional sub-surface Plot watering, and twice daily spraying to prevent the surface from drying out. Plot No. 2 was processed to a depth of one inch, using the ejector head at 4000 rpm. The processed soil was laid back on the plot and it was also watered and sprayed and received exactly the same care from then on as Plot No. The object of this preliminary test was two-fold. First, to determine if any difference in weed emergence could be noted between the two plots and secondly, to determine how long it ’would take for the weeds to start coming through in each of 1. r -90- Straight Radial Constant Angle Non-radial Straight vane Fig. 27 The three vane configurations which were mathematically investigated. 91 the two plots* Since the soil used in these tests was ob­ tained from a field that had been in sugar beets, more or less, for the past six years it was felt that the weed seeds entrained in the soil would be representatives ones and this preliminary test would give some indication of whether the mechanical application of energy to the soil would have any effect whatsoever* Other preliminary tests were started in the remaining half of the soil box using partially germinated mustard seeds in which the height of the mustard seedling after a certain number of days was measured in an effort to get some evalu­ ation of the effects of physical processing of the soil* The mustard seeds were soaked for four hours and placed on blotters in petri dishes for the initial partial germination. After the radicles started to project through the seed coat, the mustard seeds were divided into two lots. mixed with the same quantity of soil. Each lot was One soil sample with the entrained mustard seeds was processed, while the other sample v/as laid down on the soil bed. Upon processing the other sample was laid down along side it and observations were made on the emergence and rate of growth of the seedlings. Other tests were made to measure the rate of growth of the radicle in the soil. Lot samples of mustard seed were planted in rows and periodically a given sample of the row was carefully dug up to expose the roots and the roots were measured. This data on the rate of root growth proved -92- valuable in the formulation of the criteria for the GVI index for this particular type of processing. It was realized that the criteria upon which the GVI was based in the heat pro­ cessing would not be the same as those for soil conditions; thus, these tests served a useful purpose. Other tests on the two types of heads were performed with one-half inch cubes sawed from pine lumber. These tests furnished further proof that the percussion head was greatly inferior to the injection head in terms of its ability to inpart mechanical energy to 100 percent of the soil. It was found in preliminary tests with soil samples that the per­ cussion head permitted a number of clods to be in the pro­ cessed soil taken from the machine. the ejection head. This was not true with In the ejection head all of the soil is given a high velocity and forced against the circular impact plate surrounding the head, while with the percussion head it seemed that a part of the soil managed to slip down between the rotating bars. The pine block tests gave very good veri­ fication of this hypothesis for the difference in action of the two heads. At 4800 rpm. none of the pine blocks escaped breaking, or at least cracking, while always a small pro­ portion of the blocks escaped unscathed through the percussion head bars. After these preliminary tests were completed, and some indications were already apparent as to the ability of the senocidoneter to reduce the GVI of the entrained seeds, more z* -93- elaborate tests were undertaken for the purpose of deter­ mining the effect of germination time upon the reduction in GVI* These tests were performed as follows: Mustard seeds were soaked for four hours, then the soaked seeds were planted one-quarter inch deep in sixteen rows across the soil box. Immediately upon planting, two of the rows were scooped up with a specially made implement to ob­ tain a strip of soil three-quarters of an inch deep and four inches wide. This strip of soil was then processed, using the ejection head operated at 4800 rpm. more rows were likewise processed. Eight hours later two This eight hour interval was maintained until a total time elapsed of 48 hours for the last two strips between the planting and the processing time. The other two rows were not processed and were used as checks to be used as the base upon which the GVI was calculated. The rows for each time test were picked at random and the GVI calculated for each time in duplicate. These duplicate tests were quite consistent but there was a chance that the con­ sistency was accidental so three more, that is triplicate tests, were run at the same rpm. and using the same head and time intervals between planting and processing. A statistical analysis of variance was run on these five replicated tests and the results proved most satisfactory. The encouraging nature of the results of the 4800 rpm. tests naturally lead into the question of what effect a variation of rpm. would have upon this time— GVI relationship. -94- Consequently, similar tests using triplicated rows were run at 4000 and 3000 rpm* The rpm— GVI-time relationship having been obtained, it now appeared that an analysis of the mechanical energy method would not be complete without some information concerning the power or energy requirements* Thus, power consumption data was obtained for the motor under the following conditions: (1) Motor and variable speed drive operating with V-belt pulley removed, at output rpm corres­ ponding to 4000 and 4800 rpm for the head. (2) Motor and variable speed drive operating the vertical shaft through the V-belt and pulleys but without head attached. (3) The complete system of motor, variable speed drive, V-belt, shaft, and ejection head, but without soil being processed. (4) Same set-up as (3) except percussion head re­ placing ejection head. (5) Total average power input during a measured time for a measured quantity of soil being processed at both 4000 and 4800 rpm* With this data, the mechanical energy per unit of soil could be obtained. Also, estimates as to the efficiency of this type of energy application could also be made. The Results The comparison test of the processed plot and the un­ processed plot showed two encouraging results. data is shown in Appendix III. The original From this data it was evident that almost all of the weed seeds emerging from both plots v/ere from depths less than three-quarters of an inch. totals show this to be 96,3 percent. The It is obvious that some degree of caution must be used in using this figure as proof that seeds normally do not germinate below three-quarters of an inch, since two qualifying factors must be considered. First, the experiment v/as carried for only 12 days, thus some of the deep germinated seeds would not have yet appeared. Also, the experiment was performed indoors under fluorescent lights rather than outdoors with sunlight and the daily temperature fluctuation. Even with these qualifications, the data seems to give some substantiation to the hypothesis that a shallow strip free from weed seeds would give a decided impetus to the growth of sugar beet seedlings. The other obvious conclusion that can be drav/n from the data in Appendix III is that only 4.8 percent of the total seedlings came up in the plot that had the blanket of processed soil on it. The least that can be said for this preliminary data is that it gave encouragement to further investigation into the mechanical treatment of the soil strip. The next of the preliminary tests which was carried on concurrently with the comparison test concerned the height of 96 seedlings from processed and unprocessed conditions. One hundred, pre-selected, soaked seeds were randomly divided into lots of 50 each. Each lot of 50 seeds was thoroughly mixed with one-half pound of moist processed soil. The soil and seeds from Lot 1 were reprocessed at 3000 rpm and then laid back in the soil box. The soil and entrained seeds from Lot 2 were laid directly in the seed box without reprocessing. They were the controls. Seventy-two hours later stand counts were made of the two lots. In Lot 1, the processed seeds, the heights of the seven seedlings above the ground were as fo H o w s : 2, 2, 2, 3, 7, 8 and 20 mm. In Lot 2, the control, 42 seedlings were above ground, with 40 of them over 20 inn. high. Here again, the indications were positive and .gave further encouragement to proceed with a more detailed analysis of the factors involved. The next series of tests were the ones in which the germination time before processing was varied to determine its influence upon the germination vitality index. The results of five replicated tests using the ejection head at 4800 rpm are shown in Figure 28. As a result of previous tests, the criteria for determining the germination vitality index were slightly modified from that used in the heat energy studies. The main modification was in the time requirement. In the heat energy studies a time of four days was allowed before the checks on radicle and cotyledons were made, whereas in the studies of the seeds germinating in soil, the time was , Germination Vitality Index CO 8 O 8 o o 8 TT / Vt/* /I} st '/ / 3 Bv*' s to CD / to rr^r Si f 8? *% o *1 o O I fcr o * / m'+M ? Gfe f fhf CD // V if H /*11 /'// / n is v -A6- y-* 0 to 1 o o c* »-* o p w leiigthened to fivedays. However, all gemination vitality index figures used in this section on mechanical application of energy are based upon the same eriteria for determining the GVI. The results of additional tests replicated three times for speeds of 4000 rpm and 3000 rpm are given in Figure 89 and Figure 30* During the planning of the GVI tests at the three head speeds it was not known how many replications of each test would be neoessary to give assurance that the variations would be due to the germination time before processing, rather them, to random variables* n m at 4800 rpm. Duplicated tests were first The resulting data showed that the germi­ nation time before processing did have considerable effect upon the GVI* However, considerable variation existed be­ tween the individual tests so the tests were repeated three more times and an analysis of variance was run on the five replications. The F value obtained was 84, which indicated that there was considerably less than one chance in a thousand that the relationship shown by the data would be due to chance factors* As the results of this extremely high F value the series of tests for the other two speeds were only triplicated, rather than replicated five times. As a check on this judgment an analysis of variance was run on the data for the 3000 rpm tests. The F value was now reduced to 14, but still far above the value of 4 which corresponds to the probability of one chance in a hundred of the results being due to accident* GERMINATION VITALITY INDEX 78 I 110 GEHMINATION TIME BEFORE PROCESSING \ \ \ 100 EJeotion Head \ \ 4000 rpa \ \ #102-23 \ 60 \ - \ \ N \ ^ \ I \ i «0 e I ' i ► N \\ \\ v\ 40 \ \ \ \ £ \ \ \ £0 ■V \ \ \ 8 16 24 32 Gemination Tine Before Processing, rpa rig. 29 40 40 GERMINATION TITALITT INDEX 78 GERMINATION TIME BEFORE PROCESSING no EJeotion Head 3000 rpm 0* 80 \y 60 s 40 -100 tlon Vitality Index |bs-16 \ \ e O 20 8 16 24 32 Oerainatloa Time Before Processing, hours Fiff. 30 40 48 -101- For comparison purposes, the general trends of the curves in Figures 28, 29 and 30 were combined into one graph so that the interacting effects of speed and time on GrVT could be more easily visualized. Figure 31. This combined graph is shown in From this we see that very little reduction in GVI is obtained during the first 16 hours of germination time. Previous tests on rate of germination gave indications of why this might be so. Pre-soaked seeds, such as were used in all these tests, required between 12 and 20 hours germination time in the soil before the radicle would break the seed coat. So the evidence strongly suggests that the break point where the curve’s slope start increasing more rapidly occurs about the place where the seed coat has been ruptured and the radicle becomes exposed to direct mechanical damage. Another interesting aspect of the curves shown in Figure 31 is the fact that some of the seedlings escaped drastic damage at the lower rpm, even though germination had proceeded to the point where the radicle v/as 5 to 10 mm. long, which occuredat about 40 to 48 hours germination time. This factor would be of considerable importance if it became necessary to require complete kill of the weed seedlings. It has been noted that for the same pre-germination time, processing at 4800 rpm. produces a considerably greater re­ duction in GVI but the power consumption would be more be­ cause of the higher speed. be seen. JXist how much more now remains to The power requirements at 4000 and 4800 rpm for various conditions of the semocidometer are itemized in Appa Effeot of Speed k Time upon Germination Vitality Index 100 Trends from Figs. 28,29 k SO -102 Vitality index 3000 rpm Germination 4000 rpm 0 8 Id 24 32 Germination Time Before prooessing, hoars 40 48 103- Seventy-five percent more power is required to operate the head at the higher speed. OTiis checks closely with the rule of thumb used in mechanical engineering to give the in­ creased power requirement for ah increase in fan speed. This rule states that the power requirement goes up as the cube of the increase in speed. We see that the speed ratio is 1.2 and this cubed would be 1.73 which corresponds very closely with the ratio of 1.33 which is 1.75. This fact calls attention O'.V& to one of the basic characteristics of the ejection head, which is its fan-like action. also some disadvantages. This has some advantages and The fan action helps keep the impact plate from clogging, and also causes some suction at the soil entrance hole, which helps the feeding operation considerably. Among its disadvantages are the above mentioned higher power consumption and the fact that it stirs up a considerably larger amount of dust than the percussion head. In summing up the power requirements, the figure most useful to keep in mind would be the last mentioned one in Appendix IV which is: 1.6 horse power required to emergize the soil at 4000 rpm with soil being processed at the rate of .34 pounds per second; and 1.8 horse power required at 4800 rpm at the same processing rate. -104- COMPARISON OF METHODS Three methods of applying energy to weed seeds in order to reduce their germination vitality and initial rate of growth have been presented. The second of these discussed, ultrasonic energy, did not seem to have characteristics that would lend itself to field application of the energy to seed while in the soil. energy The inherent limitation of ultrasonic application lies in its inability to be transferred any distance through a material other than a liquid. Air is one of the best insulators there is for ultrasonic energy. Also solids of any thickness will absorb the energy and it would seem to be extremely difficult to be able to transfer the energy into the interior of a volume of soil. In addition to the above the deciding disadvantage was that the ultra­ sonic energy, on the basis of preliminary investigations ex­ tending over a period of two months, was found to have little value in treating seeds, other than by thermal heating. The experimental work completed with ultrasonic energy appli­ cation left some degree of uncertainty as to the extent of the debilitating effects upon the seed other than thermal heat. However, it was felt that the problem could not be nursued further, and the application •of ultrasonic energy to " weed seeds was discontinued. 105 Considerable experimental work was undertaken to find the heat energy required to reduce seed germination vitality and initial rate of growth. This experimental work took the form of finding the time-temperature requirement to reduce the germination vitality index by a given amount. This data then served as the foundation upon which calculations could be made as to the amount of heat energy that would have to be applied to the soil with the entrained seeds to obtain a reasonable success in inhibiting weed seed germination in the processed soil strip. The calculations in Appendix I showed this heat energy to be about 55 BTCJ per foot of row. This figure is based upon an almost complete kill of all germi­ nating weed seeds in the soil. Since the longer the weed seed has been germinating at the time of processing, the more re­ sponsive it will be to heat injury, It would be possible to reduce this heat requirement some at the expense of some sac­ rifice in efficiency of weed control. The nature and extent of the drying action of the heat energy on the soil is a problem that would need be investigated along with the efficiency in field application of this method. Sxperiments with two different principles of mechanical energy application to the seeds entrained in soil samples v/ere made. They were the percussion head principle, wherein rotating bars strike the soil as it passes by, and the other principle wherein soil is given kinetic energy and thrown against an impact plate where, presumably, the germinating weed seeds can be debilitated. Both of these ways of applying energy have good possibilities for field use. The main ad­ vantage of the percussion head method is its lower power con­ sumption. Also, the machine is more nearly free from dust and has a higher capacity for its size. Laboratory tests on the particular models of the machines constructed, however, shov/ed that the percussion method had a serious disadvantage, at least for laboratory work. Hiis disadvantage was the in­ ability of this process to completely kill weed seedlings that had germinated and had radicle projections even up to 10 mm. The injection head, because of its characteristic of complete kill of these weed seedlings, was studied in some detail and the results were reported in the previous section. As was pointed out previously, partially germinated seeds should be more sensitive to mechanical injury and the results have substantiated this hypothesis. It was also pointed out that weed seeds that had not started the gemination process vrould be of only minor importance in any situation where it was desired to maintain a strip of soil relatively free of weeds for a period of a week or so. The application of mechanical energy fits into this picture very well and seems to have good possibilities for further development in the field. -107- As to the power requirement for applying this mechanical energy to the soil strip the figures given in Appendix IV apply only to the small laboratory machine that was con­ structed primarily for testing the theory of operation and not for efficient utilization of power. If we were to talte the figures for the 4000 rpm ejection head and extrapolate them into field conditions, we would find that a 4-row planter traveling two miles per hour would require about 75 horse pov-rer to completely process the 4 by 3/4 inch strip. A full sized field machine undoubtedly could be constructed to utilize the power much more efficiently and its horse power figure has a good possibility of being reduced by a consider­ able percent. A further reduction in this figure could be affected by foregoing part of the GVI reduction by means of a slower head rpm. Both the heat energy and the mechanical energy methods appear to have excellent chances of succeeding in field tests. There does not seem to be any intrinsic limitation in either method that would prevent it from operating at any desired germination vitality reduction efficiency. The mechanical energy method appears to have the advantage as far as simplicity of design of equipment to do the job on a field basis and field tests should be instigated to investigate these possibilities. -108- APPKNDrX I Assumptions and Calculations of Heat Energy Required for Soil Processing Assumptions: Soil type - clay loam Soil moisture - 18# (dry basis) Specific Volume - Measured value of 1.056 gm. per cu. cm. for 13.4# soil moisture, dry basis. Soil strip size - 4 inches wide by 3/4 inch deep. Soil temperature before processing 60 deg. P. Soil temperature during processing 150 deg. F. for 6 seconds. GVI of 40 for no radicle projection. GVI of 3 for 1-4 mm radicle projection. (this data from Fig. 8) Specific heat of the soil - value of 0.20 Btu per lb. per deg. F. obtained from Hall (21) and Keen*(29). *niis value is for dry clay loam. Efficiency of heat conversion - 80#. Calculations of Heat Energy Required: 1.056 sp. gr. is .0382 lbs. per cu. in. Water is .036 lbs. per cu un. •03824.036 (18 - 13.4) - .040 lbs. soil per cu. I S 5 ---- In. at 18# moisture. (1.00 - .18) x .20 - .164 Btu per lb. per deg. F. (for soil alone). .18 x 1 = .18 Btu per lb. per deg. F. (for moisture alone). 109- •164 4 *18 s .344 Btu per lb, per deg. F. for 18$ moisture soil. Cubic inches per foot of row * 4 x 3/4 x 12 s 36 cu. in. per foot of row. So then Btu per ft, of row is: 36 x ,040 x .34 x (150 - 60) x l/,8 « 55 Btu per foot of row. -110- APFENDIX II Analysis for Shape of Ejection Hood Vane Lot w w bo curve OC ddoh rototoo about 0 with ootiotont nlocitjr Uf BoUtlon assumed counter clockwise. U » m m moves out on curve OC due to centripetal force. o / /* / / Friction between a and T&ne OC rotordo outward movement. Wo first wish to determine the velocity of a oo a function of r. The Solutions The external forces acting on a may be stated as follows F — The force normal to the curved vane. -vF - The force of friction drag opposite to motion of a, and tangent to vane, whore is the ooeficisnt of friction which is assumed constant. Tbs acceleration of a can be expressed as the resultant of three componentss 1. Relation Acceleration - as though cane OC wore stationary Cg - Outward acceleration along the cane and tangential to it. ▼B2 — Acceleration due to curvature of vane OC, where ve is tangential velocity of m» and Rg is radius of curvature. 2. Entrained Acceleration — acceleration of a as though r remained constant -111- r and -/rF s a-afc, than by eliminating F and ■ after substituting in equations (1) and (2), ue obtain ■+• 2s*f c u V ^ - rcuZ(c*S

and r 3 U radians per second r0 r 1.5 Inches r^ s 6.0 Inches ^4 s *8 The solution of (6) and (7) gives a value of r^ s 906 Inches per second. The tangential velocity of the soil, mass m, at Is 1884 In./sec, so the total velocity equals 2090 in./sec. d -113« Case II - C o M U m t mtli Omrxl y « » l u t tha rotating tha rsdiui tum OC be of sooh ahapa that tha angle bati r and its tangent Tan <* = a be a constant Con r ^ o * z k r - r d£ - C', j r x in r + C . When 0 =0, r -K> , f° C “ = ~ (n T, , Then cet «f •O = In r - (n Ti ■ When 0 -JH , r * r, , fe cot et = A In (JL\ or cat « • 6 z if \n) Equation of constant angle curvet 5 T , or 0 = 2L In r - In r* z In r, - In r* let R_ bo the radius of curvature at angr point along the curved vans « (T*• tIj2) T + Z f ~ TT‘ -114- $y d & f f m n U a g (8) and fnbatitufcljy n l w a of ^ /i.. v ■ow lot r0 - 1.5 1wohM| Rc = 2 4l X - and r* , * - 6.0 inches, - .8 aa before; « - / 3*6 48.5% ds - I.33S d r . Substituting la aquation (3) and alapl1fjriag, r - 5-34 - (r)2 + soz r 4 K 1.306 ■ - *fLnr- .405 1 93,3oor = o (10 Tha eceonrt tarn prevents a alaple aolutlon but for m i n i of r S 6 inches, tha error in neglecting It la about 0.5 percent, eo the following la understood to be only appraxinate. r + soz r - 93,300 r = o m Solving the differential equation and applying the onan boundary oondltlooi aa In Caae I, / mst r~.274\4.40e ■+■ , I44.3T r = /7r(e Proa (12) and (13), - t46.3t\ (jz -646.3t) e ) - e ) (n r ~ 144*3 r, or a 0* 192.6 r. Wbaa r » 6 lnrhee, a - 1155 Incheo per second. Therefore the totel velocity la 1250 inches per > -115- c*— - Mftn-rtdlU Vans - sin <9 = 2L V r,*+ 5* costp ‘Vr,* +3r r = V r,*+s* Substituting In equation (3)» 5 + L e t •**- .8, th en - co* S - * cu* r, * O (14,J co = 5/4 raet/sec.t and /i s 1.5", S t 50Z.4 S - (314)* S = 116,315 (/5> This differential equation has the following solution when the previously stated boundary conditions are placed upon It. ISit -6S3T + •z z s e 5 - 975 e f 15It 6531 - e s = i47.2[e - Now a is solved for In terms of s. S - 151.1 (s + / . z ) When so r,=e"t S s 5.81" , S — 1059 in./sec. and the total velocity equals 1920 inches per second. lz