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+The Project Gutenberg EBook of Atoms in Agriculture, by Thomas S. Osborne
+
+This eBook is for the use of anyone anywhere in the United States and most
+other parts of the world at no cost and with almost no restrictions
+whatsoever.  You may copy it, give it away or re-use it under the terms of
+the Project Gutenberg License included with this eBook or online at
+www.gutenberg.org.  If you are not located in the United States, you'll have
+to check the laws of the country where you are located before using this ebook.
+
+Title: Atoms in Agriculture
+       (Revised)
+
+Author: Thomas S. Osborne
+
+Release Date: May 23, 2015 [EBook #49036]
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ATOMS IN AGRICULTURE ***
+
+
+
+
+Produced by Stephen Hutcheson, Dave Morgan and the Online
+Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+
+
+                          Atoms in Agriculture
+
+
+
+
+                   The Understanding the Atom Series
+
+
+Nuclear energy is playing a vital role in the life of every man, woman,
+and child in the United States today. In the years ahead it will affect
+increasingly all the peoples of the earth. It is essential that all
+Americans gain an understanding of this vital force if they are to
+discharge thoughtfully their responsibilities as citizens and if they
+are to realize fully the myriad benefits that nuclear energy offers
+them.
+
+The United States Atomic Energy Commission provides this booklet to help
+you achieve such understanding.
+
+[Illustration: ]
+
+                                          Edward J. Brunenkant, Director
+                                       Division of Technical Information
+
+  UNITED STATES ATOMIC ENERGY COMMISSION
+
+  Dr. Glenn T. Seaborg, Chairman
+  James T. Ramey
+  Wilfrid E. Johnson
+  Dr. Theos J. Thompson
+  Dr. Clarence E. Larson
+
+
+
+
+                          Atoms in Agriculture
+
+
+by Thomas S. Osborne
+
+
+
+
+                                CONTENTS
+
+
+  RESEARCH IN THE UNITED STATES                                         1
+  HOW ARE RADIOISOTOPES USED IN RESEARCH?                               2
+      They May be Used as “Tracers”                                     2
+      How Effective Are Radioactive Tracers?                            3
+  PLANT NUTRITION AND METABOLISM                                        4
+      What Happens to Fertilizer in the Soil?                           4
+      Do Plants Absorb Through Roots Only?                              4
+      Where Should Fertilizer be Placed?                                5
+      Do Fertilizers Move Fast in Plants?                               5
+      What Else Do Radioisotopes Tell Us?                               5
+  PLANT DISEASES AND WEEDS                                              8
+      How Can We Combat Plant Diseases?                                 8
+      Why Do Chemicals Destroy Some Plants?                            10
+  ANIMAL NUTRITION AND METABOLISM                                      11
+      How Nutritious Are Various Feedstuffs?                           11
+      Can Lean Meat be Estimated “on the Hoof”?                        12
+      Does Thyroid Affect Milk—Egg Production?                         13
+      More Tracers in Animal Nutrition Research                        13
+  INSECTS                                                              15
+      Where and How Fast Do Insects Travel?                            15
+      How Far Do Insects Carry Pollen?                                 15
+      Are Predators Used to Destroy Insects?                           16
+      Can Tracers Measure Spray Residues?                              17
+  RADIOISOTOPES AS RADIATION SOURCES                                   17
+      Can Radiation Produce New Plants?                                18
+      Can Radiation Destroy Germs and Insects?                         19
+      How Does Radiation Affect Farm Animals?                          22
+      What Else Can Radiation Tell Us?                                 22
+  CONCLUSION                                                           23
+  SUGGESTED REFERENCES                                                 24
+
+
+                 United States Atomic Energy Commission
+                   Division of Technical Information
+           Library of Congress Catalog Card Number: 64-60274
+                            1962; 1963(Rev.)
+
+
+ABOUT THE AUTHOR
+
+Thomas S. Osborne is in charge of plant-breeding research being
+conducted by the University of Tennessee’s Agricultural Research
+Laboratory for the Atomic Energy Commission. He has been in this work
+since 1953.
+
+But Dr. Osborne is a teacher at heart. Hence when students wrote
+inquiring about the effects of radiation on seeds, he took great
+interest in replying. From these replies grew mimeographed literature
+suggesting experiments for students; then this and other booklets.
+
+Dr. Osborne received his undergraduate degree from Oklahoma State
+University and his doctorate from Washington State University.
+
+
+
+
+                          Atoms in Agriculture
+
+
+by Thomas S. Osborne,
+Associate Professor of Agronomy, University of Tennessee.
+
+  _To know what questions to put to Nature—that is 95 per cent of
+  scientific research._
+                                                              —Whitehead
+
+If man’s existence on the earth is compared to a calendar year, then he
+began farming in the very early morning of December 30 and began
+applying systematic knowledge to agriculture at 10:15 p.m. on December
+31.
+
+The first traces of man on the earth are dated at about one and
+three-quarter million years ago. Plant life then was very much like
+plant life today, but the animal population was quite different. Man
+became a producer of plants and animals instead of merely a gatherer and
+hunter about 8000 years ago. He has applied systematic study to
+cultivated plants and animals for only 300 years.
+
+
+
+
+                     Research in the United States
+
+
+Estimates of crop losses in the United States each year are
+approximately $5 billion to weeds, $4 billion to insects, and $3 billion
+to diseases. This total loss of $12 billion a year is about $22,500 a
+minute.
+
+In an effort to reduce these losses and to raise the standard of living,
+agricultural research has become more specialized and more complex. Over
+the years it has gradually changed from trial-and-error attempts to
+increase production to the actual study of basic questions. To study
+such intricate systems as the leaf of a plant or the liver of an animal,
+agricultural science has had to draw from every other science. The use
+of radioactive tracers and radiations in research looks especially
+promising to agriculture.
+
+In fact, agriculture has already begun to benefit from the applications
+of such research. Radioactive techniques have been used to study soils,
+plants, microbes, insects, farm animals, and new ways to use and
+preserve foodstuffs. Radioactive atoms are not used directly by farmers
+but are used in research directed by the U. S. Department of Agriculture
+and Atomic Energy Commission, by the agricultural experiment stations of
+the various states, and by numerous public and private research
+institutions. From such research come improved materials and methods
+which are used on the farm.
+
+In more highly developed countries agricultural research has brought a
+shift of emphasis from production to utilization. In the United States
+today, each farmer produces enough food for himself and 25 other people.
+Moreover, for every person who works on a farm, there are two or three
+other people who sell him goods and services or process and distribute
+the things he produces.
+
+In agriculture, as in all areas of research, the number of questions to
+be asked of Nature seems infinite. Future generations seeking to answer
+these questions will probably rely more on techniques using radioactive
+isotopes than on any other methods known today.
+
+
+
+
+                How Are Radioisotopes Used in Research?
+
+
+They May Be Used as “Tracers”
+
+Man’s attempts to describe the universe consist of finding answers to
+the questions he puts to Nature:
+
+  How deep is a well? Toss in a rock.
+  Where is the cat? Hang a bell on him.
+  How far does a wild duck fly? Put a marker on his leg.
+  Where are the fireflies? Just watch at dusk.
+  Is our satellite still up? Listen for the radio signal.
+
+Other questions arise in agricultural research:
+
+  How fast do roots grow? How deep? How soon does water get to them
+              after a rain?
+  When does a mouthful of hay reach a cow’s stomach?
+  How long until nutrients get into her blood? Her milk?
+  How far will pine pollen travel on the wind?
+  How deep does an earthworm burrow?
+
+To answer these questions, scientists need some kind of miniature genie,
+one who will shout at the proper moment, “I’m here!” When the root has
+reached the fertilizer or the water has reached the root; when the hay
+becomes transmuted to milk, or the earthworm arrives at a particular
+spot—then this invisible little servant who has made the trip could
+announce, “I’m here!”
+
+Such a helpful genie exists as the radioactive atom: he is invisibly
+small, obedient, transportable, digestible, immune to fire, flood, or
+famine, able to travel under his invisible cloak to the secret hiding
+places of Nature’s creatures and announce to waiting Geiger tubes, “I’m
+here!”
+
+The physically unstable radioactive atom behaves chemically exactly like
+its stable counterpart until the instant it emits its radiation and
+becomes stable. For example, radioactive phosphorus behaves,
+biologically and chemically, like stable phosphorus until it emits a
+beta particle and becomes stable sulfur. If the beta particle enters a
+gas-filled Geiger tube, it produces a tiny burst of electrical energy
+which is registered by the counter.
+
+Like fireflies which reveal themselves at dusk by flashes of light,
+radioisotopes announce their numbers and locations to sensitive Geiger
+tubes by flashes of invisible “light.”
+
+
+How Effective Are Radioactive Tracers?
+
+One way to see how valuable radioactive tracers are is to compare them
+to standard chemical techniques. A sensitive chemical test can perceive
+molecules as dilute as 10⁻⁷; that is, it can detect a molecule
+surrounded by 10 million molecules of another kind. A good radioactive
+tracer technique, by comparison, can distinguish concentrations of
+10⁻¹¹; that is, it can trace one in 100 _billion_.
+
+In other words by the chemical test you could find a person in
+metropolitan New York with a secret tattoo on the roof of his mouth. By
+the tracer method you could find this same person anywhere in the world,
+even if the world population were multiplied fiftyfold.
+
+In the chemical test you could distinguish the equivalent of one kernel
+of corn in one-tenth of a boxcar load; in the tracer, one kernel in 850
+boxcars.
+
+
+
+
+                     Plant Nutrition and Metabolism
+
+
+Most studies of plant nutrition and metabolism pertain to the following
+questions. What do plants need for their best growth? How do they take
+in the materials they need? What things are absorbed by roots and what
+things by foliage? How does the plant turn water and other simple
+compounds into carbohydrates and proteins?
+
+Specific problems that atomic energy has helped to solve are listed.
+
+
+What Happens to Fertilizer in the Soil?
+
+Early research indicated that only 10 to 12 per cent of phosphorus
+fertilizers was taken up by plants in the first year; the rest was
+“locked into” the soil or washed away. With radioactive phosphorus-32
+scientists found that as much as 50 to 70 per cent of the phosphorus in
+a plant came from the fertilizer during the first two or three weeks of
+growth.
+
+
+Do Plants Absorb Through Roots Only?
+
+Fertilizer applied to soil is largely wasted because it is either bound
+by soil particles or is washed out of the root zone. If chemical
+elements could go directly into leaves and bypass the wastefulness of
+soils, a tremendous saving would result.
+
+Botanists have learned in recent years that the foliage of plants can
+take in some nutrients much as roots can. With tracers they discovered
+that many nutrients are readily taken up by foliage, including bark of
+dormant trees, even at temperatures below freezing. As shown by isotopic
+tracers, elements such as phosphorus, nitrogen, and potassium move both
+up and down from the point of application at rates similar to those
+following root absorption. Urea (a nitrogen compound) is now used as a
+nutrient foliar spray for many fruit and vegetable crops in this
+country.
+
+
+Where Should Fertilizer Be Placed?
+
+Even before the use of tracers, agronomists realized the inefficiency of
+spreading fertilizer uniformly over a seed-bed. They know the fertilizer
+should be placed somewhere near the seed, but where? Above? Below?
+Beside? Below and beside? How far away? They had conducted some
+research, but the methods were slow and tedious.
+
+Using tracers, the researchers confirmed earlier findings that roots
+within two or three days reached fertilizer placed less than two inches
+directly below seeds, but the roots tended to congregate there. When the
+fertilizer was two inches below and two inches to the side, roots
+reached it within a week and a better root system developed. With three
+inches between seeds and fertilizer, the desired seedling “boost” was
+delayed three or four weeks. (See Fig. 1.)
+
+
+Do Fertilizers Move Fast in Plants?
+
+The movement of radioactive phosphorus from root to leaf was found to be
+remarkably fast, sometimes requiring less than twenty minutes. (See Fig.
+2.)
+
+
+What Else Do Radioisotopes Tell Us?
+
+Some plants take in chemicals that the plant probably cannot use: for
+example, the so-called locoweeds accumulate enormous amounts of
+selenium. With tracer techniques, we can see that the root uptake
+process has poor powers of discrimination.
+
+Fig. 1—Soil tests tell _how much_ of each fertilizer element is needed
+but not where to put it to give seedlings the much-needed “push.” With
+tracers it is found that:
+
+[Illustration: (A) Fertilizer mixed throughout the soil gives the least
+benefit to seedlings.]
+
+[Illustration: (B) If placed in a band below and beside the seeds, the
+fertilizer gives high uptake and good root distribution.]
+
+[Illustration: (C) If the fertilizer is placed directly beneath the
+seeds, highest uptake occurs but roots tend to “bunch”—a handicap to
+later growth.]
+
+Fig. 2—Radioactive plant nutrients injected in soil roots
+
+[Illustration: have not reached above ground parts in 5 minutes]
+
+[Illustration: but have, as indicated by Geiger counter, reached these
+parts in 20 minutes.]
+
+[Illustration: ]
+
+Tracer experiments reveal that roots cannot distinguish potassium
+(needed in large amounts) from other elements which are chemically
+similar but quite different in size. Once inside the plant, only
+potassium can be metabolized and similar but heavier elements (rubidium,
+cesium) are useless. This is like an absentminded builder who buys
+brick, boulders, and gravel indiscriminately for his wall and then finds
+he can use only part of his materials.
+
+The process called photosynthesis whereby green plants use energy from
+the sun to convert simple compounds from air and soil into complex,
+energy-rich substances has been termed the most important chemical
+reaction in the world. It is the basis for man’s entire food supply and,
+except for nuclear energy, all significant fuel as well. Tracer
+techniques have multiplied the research efforts on photosynthesis
+tremendously.
+
+When only chemical tests were available, food manufacturing in green
+leaves had to progress for hours before scientists could measure the
+products. But with tracers and other new techniques they have narrowed
+the experimental time to minutes and finally to seconds. Today they know
+that a green leaf has formed sugars more complex than fructose, “fruit
+sugar,” after exposure to light for only _one second_!
+
+When the incredible complexities of photosynthesis are finally
+unraveled, radioactive tracers, especially radioactive carbon-14, will
+have provided the significant clues.
+
+
+
+
+                        Plant Diseases and Weeds
+
+
+How Can We Combat Plant Diseases?
+
+At one time to stop epidemic spread of plant diseases was virtually
+impossible; farmers had to abandon fields and crops. Such catastrophes
+caused by microbes have changed the course of history. For example, the
+Irish famines of the 1840’s resulted from the potato blight and caused
+mass emigrations from Ireland.
+
+In this country today plant diseases result in losses estimated at $3
+billion a year. So far, the most economical means of reducing the
+ravages of plant diseases has been to breed resistant plant varieties.
+Although such a variety may cost $100,000 to develop, its cost is
+usually repaid within a year or two.
+
+But the victory is only temporary. Although plants are bred to resist
+the pathogen (fungus) of the moment, Nature is constantly changing the
+microbial population by mutation and hybridization. Within a few years
+virulent strains of fungi which can attack the “resistant” variety
+increase to such an extent that the new variety must be replaced.
+
+For crops that provide high per-acre income such as some vegetables and
+vine and tree fruits, chemical control of fungous diseases is
+economically possible; in fact, it is a real necessity. But such
+treatment is too costly for most field crops, unless some cheap seed
+treatment or fertilizer additive can be found.
+
+A general breakthrough in control of plant diseases is yet to come.
+Because of thousands of pathogenic species, with hundreds of strains, it
+does not seem possible that the following questions could be answered
+about each one. What is the life cycle of the microbe? What conditions
+of temperature and humidity encourage it to spread? What plant species
+does it attack? How does it enter? What chemical changes within the
+cells of the plant determine whether they resist or succumb to the
+invader? How long can germs remain potent? How far can they travel by
+wind or water? What combination of resistant varieties, cultural
+methods, and chemical treatment will control the disease?
+
+With tracers it is possible for the first time to measure chemical
+uptake in single spores and to follow chemicals through the plant.
+Perhaps the most enlightening information from such studies is that some
+fungicides are 10,000 times less effective per unit of “body weight”
+than are other chemicals used to destroy weeds and insects. Obviously
+the breakthrough in chemical control of plant diseases is yet to come.
+
+
+Why Do Chemicals Destroy Some Plants?
+
+Weeds cost this country an estimated $5 billion annually, which is more
+than the loss to either plant diseases or insects. Selective chemical
+weed killers such as “2, 4-D” have become so widely used that more than
+$135 million worth was sold in the United States in 1959. In proper
+concentration these compounds will destroy many unwanted plants without
+harming lawn grasses or crop plants.
+
+[Illustration: Fig. 3—Tagged weed-killing chemicals (A) are taken in and
+transported alike in grassy (B) and broad-leaved (C) plants, but only in
+the latter are killed.]
+
+As in many other instances, beneficial use of the chemicals has far
+outreached an understanding of how they work. The still scanty knowledge
+of the process has come almost entirely from tracer studies.
+
+All plants readily absorb selective weed killers (“herbicides”), which
+are not destroyed within the plants. Resistant plants show no effect of
+the chemicals, but sensitive plants suffer damage in actively growing
+roots and shoots. Sugar formation during photosynthesis is disrupted in
+these plants, and phosphorus movement is retarded. In order to predict
+what new classes of chemicals might be of value as herbicides, we must
+await the results of research using radioactive tracers.
+
+
+
+
+                    Animal Nutrition and Metabolism
+
+
+How Nutritious Are Various Feedstuffs?
+
+An endless phase of animal nutrition research deals with efficiency of
+rations, that is, the pounds gained by the animal per pound of feed
+consumed. The standard form of such research is to feed groups of
+animals on different rations for several weeks or months and determine
+average change in weight per pound of feed used.
+
+In recent years scientists have used chemical tests to compare the
+amount of calcium in the diet against the amount excreted. The apparent
+digestibility of such minerals has thus been computed for different
+rations. Yet one important source of error in these chemical tests
+plagued researchers.
+
+There is a “turnover” in nutrients fed to animals; elements in feed are
+absorbed into the animal’s body, retained for a time, and later
+excreted. For example, a cow actually loses more calcium (through milk
+and excreta) during the first six months of milk production than her
+normal ration contains. As long as the amount of recycling was unknown,
+scientists could not tell, for instance, how much calcium in alfalfa hay
+could be digested by simply measuring incoming and outgoing calcium.
+
+Formerly scientists could study the problem only by withholding all
+calcium from the diet. Under this unnatural condition all outgoing
+calcium came from the animal’s body.
+
+With radioactive calcium in a steer’s diet (or injected into the blood),
+scientists can quickly tell how much of the excreted calcium comes from
+the animal’s blood and organs under normal conditions. In a typical
+instance a ration thought to have 24 per cent digestible calcium,
+chemically determined, was found to have 38 per cent by the tracer
+technique.
+
+The tracer method shows that milk contains phosphorus, only 20 per cent
+of which may come from the feed and 80 per cent from the cow’s bones.
+With eggs, about 65 per cent of the phosphorus is provided by feed and
+35 per cent by the hen. Radioactive tracers permit measurement of such
+“biological pathways,” as the biochemist calls them.
+
+
+Can Lean Meat be Estimated “on the Hoof”?
+
+The proof of the ration, one might say, is in the cutting. That is, the
+worth of a particular feed was formerly unknown until the carcass had
+been cut and priced.
+
+Because of the time and expense, researchers in the past have merely
+tested groups of animals on a ration for a few weeks and then estimated
+the total gain by weighing and measuring. The main drawback to such a
+method is that it measures total growth only. In meat animals, knowing
+total growth is less important than knowing how much gain is in the more
+valuable lean meat, how much is in fat, and how much merely water.
+Techniques based on atomic energy have provided a new approach without
+adding radioactive contamination to the animal.
+
+Of the “background radiation” that has existed since the earth was
+formed, part comes from cosmic rays (from outer space) and part from
+radioactive materials in the earth itself. One of these naturally
+radioactive isotopes is radioactive potassium, which is present to a
+small but significant extent in food, in human bodies, and in
+construction materials.
+
+While some chemicals such as carbon, hydrogen, and oxygen go into almost
+every kind of substance in living things, potassium plays a special role
+in animals: it lodges almost exclusively, not in bone or fat or water,
+but in lean meat.
+
+Biological and medical researchers are now cooperating to build
+“whole-body” radiation counters. A human being or an animal is actually
+enclosed by these huge devices, some of which are so sensitive they
+measure nearly every ray that emerges from the body. These counters will
+help answer many questions, but here only their use to measure
+radiopotassium in meat animals is explained. The animal is fed a test
+ration containing no added radioactivity. At intervals of a week or
+more, the animal is weighed and is also tested for natural
+radioactivity. Weighing tells total gain, while radiopotassium counting
+shows how much gain is in the desired lean meat. This method is
+remarkably simple, and since no radioactivity is added to its diet, the
+animal can still be marketed.
+
+
+Does Thyroid Affect Milk—Egg Production?
+
+Recognition of the significance of the thyroid gland in animals, the
+association of iodine with the thyroid, and the availability of an
+excellent radioisotope of iodine have resulted in increased study of
+this important gland. Chemical tests had hinted at a link between the
+thyroid gland and the production of milk and eggs. Using radioactive
+iodine, scientists learned that thyroid activity increases with the
+onset of milk and egg formation. In hot weather, when yield of milk and
+eggs decreases, activity of the thyroid gland diminishes.
+
+It may be that a dairy breeder can soon select calves for potential milk
+production because of thyroid activity as measured by radioactive
+iodine. At present he must let the animals grow and produce milk for
+several years before he chooses those to use in herd improvement. (See
+Fig. 4.)
+
+
+More Tracers in Animal Nutrition Research
+
+Female hormones in microgram amounts[1] accelerate fattening of cattle
+and sheep. Before this method can be used on animals for human
+consumption, however, it must be determined that no possible human
+injury can result from any residue. With chemical tests the measurement
+of such tiny amounts was impossible. Even with radioactive carbon-14,
+doses of hormone 1000 times normal dosage were required before the
+hormones in the flesh were measurable.
+
+Fig. 4—Future high-producing milk cows may be selected as calves,
+because of the measured activity of their thyroid glands. A minute
+amount of iodine-131 is fed and within minutes has concentrated in the
+thyroid. High concentration means high thyroid activity, which in older
+animals means high milk production.
+
+      [Illustration: Iodine-131 fed ... concentrates in thyroid.]
+
+Recently an isotope of hydrogen (tritium or H³) was linked to hormones,
+and these were fed in normal amounts to cattle. Tests 90 days afterward
+showed less than one part per billion in the meat, a big step toward
+cheaper fattening of meat animals with hormones.
+
+The use of tranquilizers has been proposed for reducing the customary
+loss of weight in cattle being shipped to market. These chemicals, also,
+are used in such minute quantities that residues could not be detected
+except with radioactive tracers. Tritium can now be used by health
+officials to study the effects of tranquilizers.
+
+
+
+
+                                Insects
+
+
+Where and How Fast Do Insects Travel?
+
+Radioactive isotopes have been used to study insects, their life cycles,
+dispersion, mating and feeding habits, parasites, and predators. Several
+hundred such studies have been made on dozens of insect species.
+
+With radioactive tracers even the smallest insect becomes more easily
+followed. As one example, nearly half a million mosquito larvae were
+tagged with radioactive phosphorus in Canada. Some of the adults from
+these larvae were later found as far as seven miles away, but most were
+recovered within one-eighth mile.
+
+In a companion study grasshoppers were labeled with the same isotope.
+Their average rate of movement was only twenty-one feet per hour, and
+after seven days their position was based entirely on random motions
+plus prevailing winds. It seems that grasshoppers have no ability to
+move toward food.
+
+
+How Far Do Insects Carry Pollen?
+
+This question is of practical importance in knowing how far to separate
+seed-fields to maintain pure varieties of plants. In the past it was
+studied by the laborious method of growing a plant having a dominant
+“marker” gene for some visible trait surrounded by plants without the
+marker. Seeds from plants at various distances from the marked plant
+were grown the following year to see how far the genetically marked
+pollen had been carried. Since such plants are normally cross
+pollinated, it was difficult to obtain strains genetically pure for
+presence or absence of the marker gene. Also, considerable testing and
+bookkeeping were involved.
+
+With tracers the answer may be found in a few days. A plant is injected
+with radioactive phosphorus; after a few days its pollen is highly
+radioactive. Flowers at various distances from the tagged plant may be
+checked daily for radioactivity. In one study with alfalfa, radioactive
+pollen was carried as far as thirty feet by bees, but more than
+one-third was deposited on plants adjacent to the labeled one.
+
+
+Are Predators Used to Destroy Insects?
+
+With insect pests, as with plant diseases, biological control is more
+economical than artificial control. The use of insecticides too often
+results in destruction of helpful insects along with pests. Limited
+success has been achieved in breeding certain plants for resistance to
+insects.
+
+Two important uses of biological control in agriculture have been made
+in recent years: importing an insect from Australia to eradicate a weed
+in California and disseminating ladybird beetles to control certain
+scale insects.
+
+Fig. 5—Identifying predators that destroy unwanted insects.
+
+[Illustration: Aphids are made radioactive.]
+
+[Illustration: Larger insects found nearby are checked for
+radioactivity.]
+
+Bumblebee has not eaten radioactive aphids, but mantis has.
+
+Helpful parasites and predators must first be identified before they can
+be used. In the case of small or nocturnal insects, this can be
+exceedingly troublesome. Tagging the pests with radioisotopes in order
+to identify the predators which consume them is much simpler because the
+most efficient predators contain the most activity.
+
+With such techniques entomologists have studied insects and animals
+which prey on unwanted aphids, mosquitoes, blackflies, and roaches. Such
+experiments may lead to a deliberate increase of certain predators to
+control injurious insects.
+
+Radioactive labeling is also valuable in studying helpful insects. In
+one case the indolence of drone bees was indicated by finding that even
+with adequate syrup in their cage they still received identical syrup
+from worker bees in an adjoining cage!
+
+
+Can Tracers Measure Spray Residues?
+
+Any material used on plants or animals to kill insects or disease
+organisms must pass rigid inspection to be sure it does not accumulate
+in foodstuffs. This is particularly true of the “systemic” poisons,
+those which are fed to plants via leaves or roots and are carried
+internally to all parts of the plant. Such chemicals can be used widely
+with nonfood plants such as cotton to kill insects feeding on them.
+
+Combining radioactive labeling with other techniques has permitted the
+researchers to show that some compounds are soon broken down into
+harmless chemicals—a big step toward acceptance for their use on food
+plants.
+
+
+
+
+                   Radioisotopes as Radiation Sources
+
+
+Earlier in this booklet radioisotopes were compared to fireflies because
+they emit flashes of “light.” Isotopes serve research in another
+important way, other than as tracers.
+
+Suppose you collected all the fireflies within a 100-mile radius and put
+them into a glass jar. Instead of an occasional twinkle, you would now
+have a steady glow of light. Similarly immense numbers of radioactive
+atoms can be compressed into a small volume to produce steady, intense
+sources of radiation. Agricultural research has answered many questions
+with the use of such radiation sources.
+
+
+Can Radiation Produce New Plants?
+
+Perhaps no biological aspect of atomic energy has so caught the fancy of
+the public as the prospect of creating new plant varieties. There is
+something mysterious about pouring invisible energy into seeds or buds
+and watching for changes in the emerging leaves and flowers. There is
+also the challenge of the lottery in being unable to predict where,
+when, or in what form the alterations will appear.
+
+Although the claims of over-enthusiastic gardeners and seed dealers
+about astonishing new plants “created” by atomic radiation are doubted,
+clear proof exists even in the restrained scientific journals of
+hereditary changes caused by radiation.
+
+From more than 30 years of scientific study, certain conclusions have
+emerged. High-energy radiations can cause sudden hereditary changes
+(mutations) in any living thing: man, animal, microbe, or plant. Any
+feature of a plant subject to hereditary control—root, shoot, leaf,
+flower, or fruit—can be altered by radiation. Most of these changes are
+undesirable; they interfere with the normal state of biological affairs.
+A very small percentage of mutated organisms is improved in some way. So
+far changes cannot be controlled or predicted.
+
+To date fourteen new strains of crop plants improved by radiation have
+been put into production in various parts of the world. These varieties
+with their places and dates of release follow:
+
+  1. “Primex” white mustard, Sweden, 1950
+  2. “Chlorina Mutant” tobacco, Indonesia, about 1950
+  3. “Shafer’s Universal” bean, Germany, about 1950
+  4. “Regina II” summer oil rape, Sweden, 1953
+  5. “Weibull Stralart” fodder pea, Sweden, 1957
+  6. “Sanilac” navy bean, Michigan, 1957
+  7. “Pallas” barley, Sweden, 1958
+  8. “N. C. 4X” peanut, North Carolina, 1959
+  9. “Florad” oats, Florida, 1960
+  10. “Seaway” bean, Michigan, 1960
+  11. “Alamo-X” oats, Texas, 1961
+  12. “Gratiot” bean, Michigan, 1963
+  13. “Pennrad” barley, Pennsylvania, 1963
+  14. “Yukon-1” carnation, Connecticut, 1963
+
+In these instances no desirable changes appeared in the plant grown
+directly from treated seeds, but they appeared several generations
+later. In most cases hundreds of thousands of plants were examined
+before the desirable ones were found. The desired changes were almost
+always accompanied by undesirable ones, and years of cross-breeding and
+“purifying” were necessary to obtain usable varieties.
+
+The technique of radiation breeding can be used on any form of life
+where large numbers can be grown and discarded at little cost. The
+output of penicillin has been increased a thousandfold by repeated
+mutations caused in the microorganism producing this antibiotic. Several
+studies on radiation breeding of poultry have been started.
+
+An ingenious reverse twist of induced mutation is being applied in the
+field of plant diseases. While some scientists are irradiating seeds and
+plants in an effort to obtain disease-resistant mutations, others are
+irradiating the fungi which cause the diseases. They hope in this way to
+foresee the new strains of pathogenic microbes that will occur naturally
+in order to breed resistant plants before the new diseases appear.
+
+Some claims have been made that radiation can stimulate plant growth,
+germination, earlier maturity, and so on. Similar benefits are sometimes
+claimed for human health. These allegations are almost never proved in
+reputable laboratories. It seems likely that radiation is stimulating,
+in the words of one authority, “only in the sense that a pruning knife
+is stimulating.”
+
+
+Can Radiation Destroy Germs and Insects?
+
+Food technologists have studied ways of preserving food with radiation
+for more than ten years. Their findings indicate that complete
+sterilization of food with radiation requires doses so high (2 to 6
+million roentgens[2]) that cost is prohibitive at present, and the food
+often becomes distasteful. These amounts of energy completely destroy
+the microbes and enzymes which normally cause food to putrefy.
+
+If radiation is to be used in preserving food, it will probably be as a
+supplement to conventional methods of heating and freezing.
+“Pasteurizing” with radiation to destroy most (but not all) of the
+microbes in meat or fruit or vegetables is accomplished with less than
+five per cent of the dosage required for sterilizing. Such treatment
+does not alter flavor or texture appreciably and could be used to
+prolong the refrigerated “life” of many fresh foods. It is the
+responsibility of the Federal Food and Drug Administration to determine
+that no threat to human welfare could possibly result before approving
+the use of high-energy radiation to preserve foods.
+
+With agricultural products stored dry, such as grain, tobacco, and wool,
+the chief agents of damage are not microbes, but insects. The loss of
+stored field crops caused by insects is estimated at $200 million
+annually in the United States. Deinfesting such goods with radiation
+doses in the “pasteurizing” range promises to be practical and causes no
+apparent change in the product.
+
+Like many other foodstuffs, potatoes are often stored for months between
+harvest and use. Precaution must be taken to prevent their deterioration
+during storage not only from decay but also from sprouting.
+
+Cold storage inhibits sprouting but is costly and has another serious
+drawback. In the making of potato chips, tubers held at low temperature
+contain excess sugar and result in darkened chips. Storage at higher
+temperatures prevents conversion of starch to sugar but encourages
+sprouting.
+
+Atomic energy promises to resolve this dilemma. Given low doses of gamma
+rays (5000 to 10,000 roentgens), potatoes may be kept at room
+temperature for a year or more without sprouting. Similar doses inhibit
+sprouting of onions. The estimated cost of irradiating tubers and bulbs
+at such doses is as low as 14 cents per ton. No chemical changes have
+yet been found in irradiated potatoes that would make them unsafe for
+eating. In fact, health officials in Canada have recently approved the
+use of gamma rays on potato tubers that will be stored and later used
+for human food. Our own Food and Drug Administration has given similar
+approval for applying gamma rays to bacon and fast electrons to wheat
+(for killing insects).
+
+An ingenious application of atomic energy to agriculture concerns the
+screwworm fly, which inhabits large areas of southern United States,
+Mexico, and the Caribbean. The fly lays eggs in open wounds of
+livestock, including navels of newly born, and the burrowing maggots
+inevitably kill the animal. In the southeastern United States, damage
+from this insect amounted to $15 to $25 million annually.
+
+In the years 1958 and 1959 more than two billion screwworm flies were
+deliberately released from airplanes over the entire state of Florida
+and parts of Georgia and Alabama. This astonishing act was a major step
+in successful eradication of the pest from southeastern United States.
+
+The entomologists who conceived this remarkable scheme had the following
+information from basic studies: the insect produces a generation about
+every three weeks. In the pupal stage males can be sterilized by 2500
+roentgens of X or gamma rays, females by 5000 roentgens. The insect can
+be reared in large numbers. Sterile males are fully competitive with
+normal males for mates. And, of course, sterile eggs do not hatch. (It
+was helpful, though incidental, that females mate only once.)
+
+After initial tests on an island in the Caribbean, a large fly-producing
+plant was set up. Flies were grown to the pupal stage, irradiated with
+8000 roentgens of gamma rays, permitted to mature, and released from
+airplanes. With 50 million flies being released weekly over Florida,
+Georgia, and Alabama, the area was smothered with sterile flies, and the
+number of eggs that hatched (from the normal native flies) rapidly
+diminished to zero. The program was continued for 18 months, and in this
+time the insect was completely eliminated.
+
+Certain other insects are being considered for the sterility-eradication
+technique. Among them are the boll weevil, European corn borer,
+mosquito, and tsetse fly. Oriental scientists are using gamma rays
+instead of the conventional heating to kill silkworms inside cocoons.
+
+
+How Does Radiation Affect Farm Animals?
+
+At a few colleges of agriculture in this country, radiation effects on
+farm animals are being studied.
+
+Although it may not be flattering to be likened to a pig or a donkey,
+the fact remains that human beings are physiologically very similar to
+swine and burros. These animals are mammals with simple stomachs and
+have the same general size, shape, and placement of organs as do humans.
+Radiation studies with swine and burros, although slow and expensive,
+should give information more applicable to humans than the more rapid
+and inexpensive studies with small laboratory animals.
+
+
+What Else Can Radiation Tell Us?
+
+Two characteristics of soils besides fertility are vitally important and
+difficult to measure. These characteristics are moisture and density.
+Moisture must be determined frequently for efficient irrigation. Density
+controls the pore space available for water and oxygen; the possible
+damage to the soil from tillage and harvesting machines is revealed by
+before-and-after tests of density.
+
+Both soil moisture and density were formerly determined by laboratory
+methods, which had two drawbacks: the methods were laborious, and they
+tested soil in an unnatural state. Today a sort of double-barreled
+radiation method can be used to measure these two soil characteristics.
+
+Neutrons are readily scattered by water but not by soil; gamma rays are
+absorbed by both soil and water. In practice the experimenter drills two
+holes in the soil a few feet apart. Into one he puts a gamma-ray source;
+into the other, a radiation detector. The reading on his detector dial
+tells him the amount of gamma rays absorbed by both soil and water.
+Replacing the gamma-ray source with a neutron source, he obtains a
+reading on absorption by water only. The difference between the two
+readings is ascribed to the density, or degree of compaction, of that
+soil in its native state.
+
+
+
+
+                               Conclusion
+
+
+Radioactive tracers and radiation sources have become indispensable to
+all phases of agricultural research. They have helped answer questions
+that seemed unanswerable. But there will always be more questions to put
+to Nature. The physicists-philosophers of 1890 were confident that they
+had obtained all significant knowledge of the physical universe.
+Discoveries of the next twenty years revealed the immaturity of that
+conviction.
+
+The modern poet Archibald MacLeish has dramatized the meagerness of
+knowledge:[3]
+
+  I will tell you all we have learned ...
+    the lights in the sky are stars
+  We think they do not see
+    we think also
+  The trees do not know nor the leaves of the grasses hear us....
+
+Perhaps the most characteristic realization of the scientist today is
+that the universe is too complex to be fully described, that concepts
+must change repeatedly to absorb new findings, and that the recurring
+miracle of life is more majestic than any formula, any computer, or any
+rocket that man’s brain can devise.
+
+
+
+
+                          Suggested References
+
+
+_Applications of Radioisotopes and Radiation in the Life Sciences._
+  Hearings before the Subcommittee on Research, Development and
+  Radiation of the Joint Committee on Atomic Energy, Congress of the
+  United States, March 27-30, 1961. Superintendent of Documents, U. S.
+  Government Printing Office, Washington 25, D. C. 1961, 513 pages,
+  $1.50.
+
+_Experiments with Radiation on Seeds._ Thomas S. Osborne. U. S. Atomic
+  Energy Commission, Division of Technical Information Extension, Oak
+  Ridge, Tenn. No. 1, 11 pages; No. 2, 30 pages, free.
+
+_Oklahoma Conference—Radioisotopes in Agriculture._ (Proceedings of a
+  conference held at Oklahoma State University, April 2 and 3, 1959.)
+  TID-7578. Superintendent of Documents, U. S. Government Printing
+  Office, Washington 25, D. C. 1959, 287 pages, $2.00.
+
+_Radioactive Isotopes in Agriculture._ (Proceedings of a conference held
+  at Michigan State University, January 12-14, 1956.) TID-7512.
+  Superintendent of Documents, U. S. Government Printing Office,
+  Washington 25, D. C. 1956, 416 pages, $3.00.
+
+_Radioisotopes in Science and Industry._ U. S. Atomic Energy Commission.
+  Superintendent of Documents, U. S. Government Printing Office,
+  Washington 25, D. C. 1960, 176 pages, $1.25.
+
+_What Can You Expect from Atomic-Irradiated Seeds?_ James L. Brewbaker.
+  U. S. Atomic Energy Commission, Division of Technical Information
+  Extension, Oak Ridge, Tenn. Not dated, 8 pages, free.
+
+
+Motion Picture
+
+(Available for loan without charge from the Division of Public
+Information, U. S. Atomic Energy Commission, Washington 25, D. C.)
+
+_Harvest of an Atomic Age_, 20 minutes, 16mm, color and sound, 1963.
+
+
+
+
+                               Footnotes
+
+
+[1]A microgram bears the same relationship to a 1000-pound steer as a
+    penny does to $4½ billion.
+
+[2]The roentgen is a measure of ionizing radiation, as the foot-candle
+    is a measure of light. In simple terms the roentgen is that amount
+    of X or gamma radiation which produces one electrostatic unit (esu)
+    of electricity in one cubic centimeter (cc) of dry air at standard
+    conditions of temperature and pressure. This may sound like a
+    trivial amount of energy, but it amounts to more than two billion
+    ionizations in each cubic centimeter.
+
+[3]From “Epistle To Be Left in the Earth.”
+
+
+
+
+                          Transcriber’s Notes
+
+
+--Retained publication information from the printed edition: this eBook
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+--In the text version only, added a brief label to each illustration;
+  and for graphs, provided tabular summaries of the data where possible.
+
+
+
+
+
+
+
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+
+<pre>
+
+The Project Gutenberg EBook of Atoms in Agriculture, by Thomas S. Osborne
+
+This eBook is for the use of anyone anywhere in the United States and most
+other parts of the world at no cost and with almost no restrictions
+whatsoever.  You may copy it, give it away or re-use it under the terms of
+the Project Gutenberg License included with this eBook or online at
+www.gutenberg.org.  If you are not located in the United States, you'll have
+to check the laws of the country where you are located before using this ebook.
+
+Title: Atoms in Agriculture
+       (Revised)
+
+Author: Thomas S. Osborne
+
+Release Date: May 23, 2015 [EBook #49036]
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ATOMS IN AGRICULTURE ***
+
+
+
+
+Produced by Stephen Hutcheson, Dave Morgan and the Online
+Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+<div id="cover" class="img">
+<img class="nc" id="coverpage" src="images/cover.jpg" alt="The Atomic Fingerprint: Neutron Activation Analysis" width="500" height="780" />
+</div>
+<h1><span class="white">Atoms in Agriculture</span></h1>
+<h2>The Understanding the Atom Series</h2>
+<p>Nuclear energy is playing a vital role in the life of every
+man, woman, and child in the United States today. In the
+years ahead it will affect increasingly all the peoples of the
+earth. It is essential that all Americans gain an understanding
+of this vital force if they are to discharge thoughtfully their
+responsibilities as citizens and if they are to realize fully the
+myriad benefits that nuclear energy offers them.</p>
+<p>The United States Atomic Energy Commission provides
+this booklet to help you achieve such understanding.</p>
+<div class="img" id="pic_1">
+<img src="images/pag001.jpg" alt="" width="300" height="100" />
+<p class="caption small"></p>
+</div>
+<p><span class="lr">Edward J. Brunenkant, Director</span>
+<span class="lr">Division of Technical Information</span></p>
+<dl class="undent"><dt>UNITED STATES ATOMIC ENERGY COMMISSION</dt></dl>
+<dl class="undent"><dt>Dr. Glenn T. Seaborg, Chairman</dt>
+<dt>James T. Ramey</dt>
+<dt>Wilfrid E. Johnson</dt>
+<dt>Dr. Theos J. Thompson</dt>
+<dt>Dr. Clarence E. Larson</dt></dl>
+<h1><span class="white">Atoms in Agriculture</span></h1>
+<p>by Thomas S. Osborne</p>
+<h2 class="c">CONTENTS</h2>
+<dl class="toc">
+<dt><a href="#c1">RESEARCH IN THE UNITED STATES</a> 1</dt>
+<dt><a href="#c2">HOW ARE RADIOISOTOPES USED IN RESEARCH?</a> 2</dt>
+<dd><a href="#c3">They May be Used as &ldquo;Tracers&rdquo;</a> 2</dd>
+<dd><a href="#c4">How Effective Are Radioactive Tracers?</a> 3</dd>
+<dt><a href="#c5">PLANT NUTRITION AND METABOLISM</a> 4</dt>
+<dd><a href="#c6">What Happens to Fertilizer in the Soil?</a> 4</dd>
+<dd><a href="#c7">Do Plants Absorb Through Roots Only?</a> 4</dd>
+<dd><a href="#c8">Where Should Fertilizer be Placed?</a> 5</dd>
+<dd><a href="#c9">Do Fertilizers Move Fast in Plants?</a> 5</dd>
+<dd><a href="#c10">What Else Do Radioisotopes Tell Us?</a> 5</dd>
+<dt><a href="#c11">PLANT DISEASES AND WEEDS</a> 8</dt>
+<dd><a href="#c12">How Can We Combat Plant Diseases?</a> 8</dd>
+<dd><a href="#c13">Why Do Chemicals Destroy Some Plants?</a> 10</dd>
+<dt><a href="#c14">ANIMAL NUTRITION AND METABOLISM</a> 11</dt>
+<dd><a href="#c15">How Nutritious Are Various Feedstuffs?</a> 11</dd>
+<dd><a href="#c16">Can Lean Meat be Estimated &ldquo;on the Hoof&rdquo;?</a> 12</dd>
+<dd><a href="#c17">Does Thyroid Affect Milk&mdash;Egg Production?</a> 13</dd>
+<dd><a href="#c18">More Tracers in Animal Nutrition Research</a> 13</dd>
+<dt><a href="#c19">INSECTS</a> 15</dt>
+<dd><a href="#c20">Where and How Fast Do Insects Travel?</a> 15</dd>
+<dd><a href="#c21">How Far Do Insects Carry Pollen?</a> 15</dd>
+<dd><a href="#c22">Are Predators Used to Destroy Insects?</a> 16</dd>
+<dd><a href="#c23">Can Tracers Measure Spray Residues?</a> 17</dd>
+<dt><a href="#c24">RADIOISOTOPES AS RADIATION SOURCES</a> 17</dt>
+<dd><a href="#c25">Can Radiation Produce New Plants?</a> 18</dd>
+<dd><a href="#c26">Can Radiation Destroy Germs and Insects?</a> 19</dd>
+<dd><a href="#c27">How Does Radiation Affect Farm Animals?</a> 22</dd>
+<dd><a href="#c28">What Else Can Radiation Tell Us?</a> 22</dd>
+<dt><a href="#c29">CONCLUSION</a> 23</dt>
+<dt><a href="#c30">SUGGESTED REFERENCES</a> 24</dt>
+</dl>
+<p class="tbcenter"><b>United States Atomic Energy Commission
+<br />Division of Technical Information
+<br /><span class="smaller">Library of Congress Catalog Card Number: 64-60274
+<br />1962; 1963(Rev.)</span></b></p>
+<h3>ABOUT THE AUTHOR</h3>
+<p>Thomas S. Osborne is in charge of plant-breeding research being
+conducted by the University of Tennessee&rsquo;s Agricultural Research
+Laboratory for the Atomic Energy Commission. He has been in
+this work since 1953.</p>
+<p>But Dr. Osborne is a teacher at heart. Hence when students
+wrote inquiring about the effects of radiation on seeds, he took
+great interest in replying. From these replies grew mimeographed
+literature suggesting experiments for students; then this and other
+booklets.</p>
+<p>Dr. Osborne received his undergraduate degree from Oklahoma
+State University and his doctorate from Washington State University.</p>
+<div class="pb" id="Page_1">1</div>
+<h1 title=""><span class="white">Atoms in Agriculture</span></h1>
+<p>by Thomas S. Osborne,
+<br />Associate Professor of Agronomy, University of Tennessee.</p>
+<blockquote>
+<p><i>To know what questions to put to Nature&mdash;that
+is 95 per cent of scientific research.</i>
+<span class="lr">&mdash;Whitehead</span></p>
+</blockquote>
+<p>If man&rsquo;s existence on the earth is compared to a calendar
+year, then he began farming in the very early morning of
+December 30 and began applying systematic knowledge to
+agriculture at 10:15 p.m. on December 31.</p>
+<p>The first traces of man on the earth are dated at about
+one and three-quarter million years ago. Plant life then
+was very much like plant life today, but the animal population
+was quite different. Man became a producer of plants
+and animals instead of merely a gatherer and hunter about
+8000 years ago. He has applied systematic study to cultivated
+plants and animals for only 300 years.</p>
+<h2 id="c1">Research in the United States</h2>
+<p>Estimates of crop losses in the United States each year
+are approximately $5 billion to weeds, $4 billion to insects,
+and $3 billion to diseases. This total loss of $12 billion a
+year is about $22,500 a minute.</p>
+<div class="pb" id="Page_2">2</div>
+<p>In an effort to reduce these losses and to raise the standard
+of living, agricultural research has become more specialized
+and more complex. Over the years it has gradually
+changed from trial-and-error attempts to increase production
+to the actual study of basic questions. To study such
+intricate systems as the leaf of a plant or the liver of an
+animal, agricultural science has had to draw from every
+other science. The use of radioactive tracers and radiations
+in research looks especially promising to agriculture.</p>
+<p>In fact, agriculture has already begun to benefit from the
+applications of such research. Radioactive techniques have
+been used to study soils, plants, microbes, insects, farm
+animals, and new ways to use and preserve foodstuffs. Radioactive
+atoms are not used directly by farmers but are
+used in research directed by the U. S. Department of Agriculture
+and Atomic Energy Commission, by the agricultural
+experiment stations of the various states, and by numerous
+public and private research institutions. From such research
+come improved materials and methods which are
+used on the farm.</p>
+<p>In more highly developed countries agricultural research
+has brought a shift of emphasis from production to utilization.
+In the United States today, each farmer produces
+enough food for himself and 25 other people. Moreover, for
+every person who works on a farm, there are two or three
+other people who sell him goods and services or process
+and distribute the things he produces.</p>
+<p>In agriculture, as in all areas of research, the number of
+questions to be asked of Nature seems infinite. Future generations
+seeking to answer these questions will probably
+rely more on techniques using radioactive isotopes than on
+any other methods known today.</p>
+<h2 id="c2">How Are Radioisotopes Used in Research?</h2>
+<h3 id="c3">They May Be Used as &ldquo;Tracers&rdquo;</h3>
+<p>Man&rsquo;s attempts to describe the universe consist of finding
+answers to the questions he puts to Nature:</p>
+<div class="pb" id="Page_3">3</div>
+<div class="verse">
+<p class="t0">How deep is a well? Toss in a rock.</p>
+<p class="t0">Where is the cat? Hang a bell on him.</p>
+<p class="t0">How far does a wild duck fly? Put a marker on his leg.</p>
+<p class="t0">Where are the fireflies? Just watch at dusk.</p>
+<p class="t0">Is our satellite still up? Listen for the radio signal.</p>
+</div>
+<p>Other questions arise in agricultural research:</p>
+<div class="verse">
+<p class="t0">How fast do roots grow? How deep? How soon does water get to them after a rain?</p>
+<p class="t0">When does a mouthful of hay reach a cow&rsquo;s stomach?</p>
+<p class="t0">How long until nutrients get into her blood? Her milk?</p>
+<p class="t0">How far will pine pollen travel on the wind?</p>
+<p class="t0">How deep does an earthworm burrow?</p>
+</div>
+<p>To answer these questions, scientists need some kind of
+miniature genie, one who will shout at the proper moment,
+&ldquo;I&rsquo;m here!&rdquo; When the root has reached the fertilizer or the
+water has reached the root; when the hay becomes transmuted
+to milk, or the earthworm arrives at a particular
+spot&mdash;then this invisible little servant who has made the
+trip could announce, &ldquo;I&rsquo;m here!&rdquo;</p>
+<p>Such a helpful genie exists as the radioactive atom: he is
+invisibly small, obedient, transportable, digestible, immune
+to fire, flood, or famine, able to travel under his invisible
+cloak to the secret hiding places of Nature&rsquo;s creatures and
+announce to waiting Geiger tubes, &ldquo;I&rsquo;m here!&rdquo;</p>
+<p>The physically unstable radioactive atom behaves chemically
+exactly like its stable counterpart until the instant it
+emits its radiation and becomes stable. For example, radioactive
+phosphorus behaves, biologically and chemically,
+like stable phosphorus until it emits a beta particle and becomes
+stable sulfur. If the beta particle enters a gas-filled
+Geiger tube, it produces a tiny burst of electrical energy
+which is registered by the counter.</p>
+<p>Like fireflies which reveal themselves at dusk by flashes
+of light, radioisotopes announce their numbers and locations
+to sensitive Geiger tubes by flashes of invisible &ldquo;light.&rdquo;</p>
+<h3 id="c4">How Effective Are Radioactive Tracers?</h3>
+<p>One way to see how valuable radioactive tracers are is to
+compare them to standard chemical techniques. A sensitive
+<span class="pb" id="Page_4">4</span>
+chemical test can perceive molecules as dilute as 10&#8315;&#8311;; that
+is, it can detect a molecule surrounded by 10 million molecules
+of another kind. A good radioactive tracer technique,
+by comparison, can distinguish concentrations of 10&#8315;&sup1;&sup1;; that
+is, it can trace one in 100 <span class="u">billion</span>.</p>
+<p>In other words by the chemical test you could find a person
+in metropolitan New York with a secret tattoo on the
+roof of his mouth. By the tracer method you could find this
+same person anywhere in the world, even if the world population
+were multiplied fiftyfold.</p>
+<p>In the chemical test you could distinguish the equivalent
+of one kernel of corn in one-tenth of a boxcar load; in the
+tracer, one kernel in 850 boxcars.</p>
+<h2 id="c5">Plant Nutrition and Metabolism</h2>
+<p>Most studies of plant nutrition and metabolism pertain to
+the following questions. What do plants need for their best
+growth? How do they take in the materials they need? What
+things are absorbed by roots and what things by foliage?
+How does the plant turn water and other simple compounds
+into carbohydrates and proteins?</p>
+<p>Specific problems that atomic energy has helped to solve
+are listed.</p>
+<h3 id="c6">What Happens to Fertilizer in the Soil?</h3>
+<p>Early research indicated that only 10 to 12 per cent of
+phosphorus fertilizers was taken up by plants in the first
+year; the rest was &ldquo;locked into&rdquo; the soil or washed away.
+With radioactive phosphorus-32 scientists found that as
+much as 50 to 70 per cent of the phosphorus in a plant came
+from the fertilizer during the first two or three weeks of
+growth.</p>
+<h3 id="c7">Do Plants Absorb Through Roots Only?</h3>
+<p>Fertilizer applied to soil is largely wasted because it is
+either bound by soil particles or is washed out of the root
+<span class="pb" id="Page_5">5</span>
+zone. If chemical elements could go directly into leaves and
+bypass the wastefulness of soils, a tremendous saving would
+result.</p>
+<p>Botanists have learned in recent years that the foliage of
+plants can take in some nutrients much as roots can. With
+tracers they discovered that many nutrients are readily
+taken up by foliage, including bark of dormant trees, even at
+temperatures below freezing. As shown by isotopic tracers,
+elements such as phosphorus, nitrogen, and potassium move
+both up and down from the point of application at rates
+similar to those following root absorption. Urea (a nitrogen
+compound) is now used as a nutrient foliar spray for many
+fruit and vegetable crops in this country.</p>
+<h3 id="c8">Where Should Fertilizer Be Placed?</h3>
+<p>Even before the use of tracers, agronomists realized the
+inefficiency of spreading fertilizer uniformly over a seed-bed.
+They know the fertilizer should be placed somewhere
+near the seed, but where? Above? Below? Beside? Below
+and beside? How far away? They had conducted some research,
+but the methods were slow and tedious.</p>
+<p>Using tracers, the researchers confirmed earlier findings
+that roots within two or three days reached fertilizer
+placed less than two inches directly below seeds, but the
+roots tended to congregate there. When the fertilizer was
+two inches below and two inches to the side, roots reached
+it within a week and a better root system developed. With
+three inches between seeds and fertilizer, the desired seedling
+&ldquo;boost&rdquo; was delayed three or four weeks. (See <a href="#fig_1">Fig. 1</a>.)</p>
+<h3 id="c9">Do Fertilizers Move Fast in Plants?</h3>
+<p>The movement of radioactive phosphorus from root to
+leaf was found to be remarkably fast, sometimes requiring
+less than twenty minutes. (See <a href="#fig_2">Fig. 2</a>.)</p>
+<h3 id="c10">What Else Do Radioisotopes Tell Us?</h3>
+<p>Some plants take in chemicals that the plant probably
+cannot use: for example, the so-called locoweeds accumulate
+enormous amounts of selenium. With tracer techniques,
+we can see that the root uptake process has poor powers of
+discrimination.</p>
+<div class="pb" id="Page_6">6</div>
+<p class="caption small" id="fig_1">Fig. 1&mdash;Soil tests tell <i>how much</i> of each fertilizer element is needed but not where to put it to give seedlings the much-needed &ldquo;push.&rdquo; With tracers it is found that:</p>
+<div class="img" id="pic_2">
+<img src="images/pag002.jpg" alt="" width="500" height="234" />
+<p class="caption small">(A) Fertilizer mixed throughout the soil gives the least benefit to
+seedlings.</p>
+</div>
+<div class="img" id="pic_3">
+<img src="images/pag003.jpg" alt="" width="500" height="233" />
+<p class="caption small">(B) If placed in a band below and beside the seeds, the fertilizer
+gives high uptake and good root distribution.</p>
+</div>
+<div class="img" id="pic_4">
+<img src="images/pag004.jpg" alt="" width="500" height="236" />
+<p class="caption small">(C) If the fertilizer is placed directly beneath the seeds, highest
+uptake occurs but roots tend to &ldquo;bunch&rdquo;&mdash;a handicap to later
+growth.</p>
+</div>
+<div class="pb" id="Page_7">7</div>
+<p class="caption small" id="fig_2">Fig. 2&mdash;Radioactive plant nutrients injected in soil roots</p>
+<div class="img" id="pic_5">
+<img src="images/pag005.jpg" alt="" width="500" height="276" />
+<p class="caption small">have not reached above ground parts in 5 minutes</p>
+</div>
+<div class="img" id="pic_6">
+<img src="images/pag006.jpg" alt="" width="500" height="296" />
+<p class="caption small">but have, as indicated by Geiger counter, reached these parts in 20 minutes.</p>
+</div>
+<div class="img" id="pic_7">
+<img src="images/pag007.jpg" alt="" width="500" height="296" />
+<p class="caption small"></p>
+</div>
+<div class="pb" id="Page_8">8</div>
+<p>Tracer experiments reveal that roots cannot distinguish
+potassium (needed in large amounts) from other elements
+which are chemically similar but quite different in size.
+Once inside the plant, only potassium can be metabolized
+and similar but heavier elements (rubidium, cesium) are
+useless. This is like an absentminded builder who buys
+brick, boulders, and gravel indiscriminately for his wall
+and then finds he can use only part of his materials.</p>
+<p>The process called photosynthesis whereby green plants
+use energy from the sun to convert simple compounds from
+air and soil into complex, energy-rich substances has been
+termed the most important chemical reaction in the world.
+It is the basis for man&rsquo;s entire food supply and, except for
+nuclear energy, all significant fuel as well. Tracer techniques
+have multiplied the research efforts on photosynthesis
+tremendously.</p>
+<p>When only chemical tests were available, food manufacturing
+in green leaves had to progress for hours before
+scientists could measure the products. But with tracers
+and other new techniques they have narrowed the experimental
+time to minutes and finally to seconds. Today they
+know that a green leaf has formed sugars more complex
+than fructose, &ldquo;fruit sugar,&rdquo; after exposure to light for only
+<i>one second</i>!</p>
+<p>When the incredible complexities of photosynthesis are
+finally unraveled, radioactive tracers, especially radioactive
+carbon-14, will have provided the significant clues.</p>
+<h2 id="c11">Plant Diseases and Weeds</h2>
+<h3 id="c12">How Can We Combat Plant Diseases?</h3>
+<p>At one time to stop epidemic spread of plant diseases
+was virtually impossible; farmers had to abandon fields and
+crops. Such catastrophes caused by microbes have changed
+the course of history. For example, the Irish famines of
+<span class="pb" id="Page_9">9</span>
+the 1840&rsquo;s resulted from the potato blight and caused mass
+emigrations from Ireland.</p>
+<p>In this country today plant diseases result in losses estimated
+at $3 billion a year. So far, the most economical
+means of reducing the ravages of plant diseases has been
+to breed resistant plant varieties. Although such a variety
+may cost $100,000 to develop, its cost is usually repaid
+within a year or two.</p>
+<p>But the victory is only temporary. Although plants are
+bred to resist the pathogen (fungus) of the moment, Nature
+is constantly changing the microbial population by mutation
+and hybridization. Within a few years virulent strains of
+fungi which can attack the &ldquo;resistant&rdquo; variety increase to
+such an extent that the new variety must be replaced.</p>
+<p>For crops that provide high per-acre income such as
+some vegetables and vine and tree fruits, chemical control
+of fungous diseases is economically possible; in fact, it is
+a real necessity. But such treatment is too costly for most
+field crops, unless some cheap seed treatment or fertilizer
+additive can be found.</p>
+<p>A general breakthrough in control of plant diseases is
+yet to come. Because of thousands of pathogenic species,
+with hundreds of strains, it does not seem possible that the
+following questions could be answered about each one. What
+is the life cycle of the microbe? What conditions of temperature
+and humidity encourage it to spread? What plant
+species does it attack? How does it enter? What chemical
+changes within the cells of the plant determine whether they
+resist or succumb to the invader? How long can germs remain
+potent? How far can they travel by wind or water?
+What combination of resistant varieties, cultural methods,
+and chemical treatment will control the disease?</p>
+<p>With tracers it is possible for the first time to measure
+chemical uptake in single spores and to follow chemicals
+through the plant. Perhaps the most enlightening information
+from such studies is that some fungicides are 10,000
+times less effective per unit of &ldquo;body weight&rdquo; than are other
+chemicals used to destroy weeds and insects. Obviously the
+breakthrough in chemical control of plant diseases is yet to
+come.</p>
+<div class="pb" id="Page_10">10</div>
+<h3 id="c13">Why Do Chemicals Destroy Some Plants?</h3>
+<p>Weeds cost this country an estimated $5 billion annually,
+which is more than the loss to either plant diseases or insects.
+Selective chemical weed killers such as &ldquo;2, 4-D&rdquo;
+have become so widely used that more than $135 million
+worth was sold in the United States in 1959. In proper concentration
+these compounds will destroy many unwanted
+plants without harming lawn grasses or crop plants.</p>
+<div class="img" id="pic_8">
+<img src="images/pag008.jpg" alt="" width="359" height="600" />
+<p class="caption small">Fig. 3&mdash;Tagged weed-killing chemicals (A) are taken in and transported alike in grassy (B) and broad-leaved (C) plants, but only in the latter are killed.</p>
+</div>
+<p>As in many other instances, beneficial use of the chemicals
+has far outreached an understanding of how they work.
+The still scanty knowledge of the process has come almost
+entirely from tracer studies.</p>
+<p>All plants readily absorb selective weed killers (&ldquo;herbicides&rdquo;),
+which are not destroyed within the plants. Resistant
+<span class="pb" id="Page_11">11</span>
+plants show no effect of the chemicals, but sensitive plants
+suffer damage in actively growing roots and shoots. Sugar
+formation during photosynthesis is disrupted in these plants,
+and phosphorus movement is retarded. In order to predict
+what new classes of chemicals might be of value as herbicides,
+we must await the results of research using radioactive
+tracers.</p>
+<h2 id="c14">Animal Nutrition and Metabolism</h2>
+<h3 id="c15">How Nutritious Are Various Feedstuffs?</h3>
+<p>An endless phase of animal nutrition research deals with
+efficiency of rations, that is, the pounds gained by the animal
+per pound of feed consumed. The standard form of such
+research is to feed groups of animals on different rations
+for several weeks or months and determine average change
+in weight per pound of feed used.</p>
+<p>In recent years scientists have used chemical tests to
+compare the amount of calcium in the diet against the
+amount excreted. The apparent digestibility of such minerals
+has thus been computed for different rations. Yet one
+important source of error in these chemical tests plagued
+researchers.</p>
+<p>There is a &ldquo;turnover&rdquo; in nutrients fed to animals; elements
+in feed are absorbed into the animal&rsquo;s body, retained
+for a time, and later excreted. For example, a cow actually
+loses more calcium (through milk and excreta) during the
+first six months of milk production than her normal ration
+contains. As long as the amount of recycling was unknown,
+scientists could not tell, for instance, how much calcium in
+alfalfa hay could be digested by simply measuring incoming
+and outgoing calcium.</p>
+<p>Formerly scientists could study the problem only by withholding
+all calcium from the diet. Under this unnatural
+condition all outgoing calcium came from the animal&rsquo;s body.</p>
+<p>With radioactive calcium in a steer&rsquo;s diet (or injected
+into the blood), scientists can quickly tell how much of the
+excreted calcium comes from the animal&rsquo;s blood and organs
+<span class="pb" id="Page_12">12</span>
+under normal conditions. In a typical instance a ration
+thought to have 24 per cent digestible calcium, chemically
+determined, was found to have 38 per cent by the tracer
+technique.</p>
+<p>The tracer method shows that milk contains phosphorus,
+only 20 per cent of which may come from the feed and 80
+per cent from the cow&rsquo;s bones. With eggs, about 65 per
+cent of the phosphorus is provided by feed and 35 per cent
+by the hen. Radioactive tracers permit measurement of
+such &ldquo;biological pathways,&rdquo; as the biochemist calls them.</p>
+<h3 id="c16">Can Lean Meat be Estimated &ldquo;on the Hoof&rdquo;?</h3>
+<p>The proof of the ration, one might say, is in the cutting.
+That is, the worth of a particular feed was formerly unknown
+until the carcass had been cut and priced.</p>
+<p>Because of the time and expense, researchers in the past
+have merely tested groups of animals on a ration for a few
+weeks and then estimated the total gain by weighing and
+measuring. The main drawback to such a method is that it
+measures total growth only. In meat animals, knowing total
+growth is less important than knowing how much gain is in
+the more valuable lean meat, how much is in fat, and how
+much merely water. Techniques based on atomic energy
+have provided a new approach without adding radioactive
+contamination to the animal.</p>
+<p>Of the &ldquo;background radiation&rdquo; that has existed since the
+earth was formed, part comes from cosmic rays (from
+outer space) and part from radioactive materials in the
+earth itself. One of these naturally radioactive isotopes is
+radioactive potassium, which is present to a small but significant
+extent in food, in human bodies, and in construction
+materials.</p>
+<p>While some chemicals such as carbon, hydrogen, and
+oxygen go into almost every kind of substance in living
+things, potassium plays a special role in animals: it lodges
+almost exclusively, not in bone or fat or water, but in lean
+meat.</p>
+<p>Biological and medical researchers are now cooperating
+to build &ldquo;whole-body&rdquo; radiation counters. A human being or
+an animal is actually enclosed by these huge devices, some
+<span class="pb" id="Page_13">13</span>
+of which are so sensitive they measure nearly every ray
+that emerges from the body. These counters will help answer
+many questions, but here only their use to measure
+radiopotassium in meat animals is explained. The animal is
+fed a test ration containing no added radioactivity. At intervals
+of a week or more, the animal is weighed and is also
+tested for natural radioactivity. Weighing tells total gain,
+while radiopotassium counting shows how much gain is in
+the desired lean meat. This method is remarkably simple,
+and since no radioactivity is added to its diet, the animal
+can still be marketed.</p>
+<h3 id="c17">Does Thyroid Affect Milk&mdash;Egg Production?</h3>
+<p>Recognition of the significance of the thyroid gland in
+animals, the association of iodine with the thyroid, and the
+availability of an excellent radioisotope of iodine have resulted
+in increased study of this important gland. Chemical
+tests had hinted at a link between the thyroid gland and the
+production of milk and eggs. Using radioactive iodine, scientists
+learned that thyroid activity increases with the onset
+of milk and egg formation. In hot weather, when yield
+of milk and eggs decreases, activity of the thyroid gland
+diminishes.</p>
+<p>It may be that a dairy breeder can soon select calves for
+potential milk production because of thyroid activity as
+measured by radioactive iodine. At present he must let the
+animals grow and produce milk for several years before he
+chooses those to use in herd improvement. (See <a href="#fig_4">Fig. 4</a>.)</p>
+<h3 id="c18">More Tracers in Animal Nutrition Research</h3>
+<p>Female hormones in microgram amounts<a class="fn" id="fr_1" href="#fn_1">[1]</a> accelerate
+fattening of cattle and sheep. Before this method can be
+used on animals for human consumption, however, it must
+be determined that no possible human injury can result
+from any residue. With chemical tests the measurement
+<span class="pb" id="Page_14">14</span>
+of such tiny amounts was impossible. Even with radioactive
+carbon-14, doses of hormone 1000 times normal dosage
+were required before the hormones in the flesh were
+measurable.</p>
+<p class="caption small" id="fig_4">Fig. 4&mdash;Future high-producing milk cows may be selected as calves, because of the measured activity of their thyroid glands. A minute amount of iodine-131 is fed and within minutes has concentrated in the thyroid. High concentration means high thyroid activity, which in older animals means high milk production.</p>
+<div class="img" id="pic_9">
+<img src="images/pag009.jpg" alt="Iodine-131 fed ... concentrates in thyroid." width="500" height="499" />
+</div>
+<p>Recently an isotope of hydrogen (tritium or H&sup3;) was linked
+to hormones, and these were fed in normal amounts to cattle.
+Tests 90 days afterward showed less than one part per
+billion in the meat, a big step toward cheaper fattening of
+meat animals with hormones.</p>
+<p>The use of tranquilizers has been proposed for reducing
+the customary loss of weight in cattle being shipped to
+market. These chemicals, also, are used in such minute
+quantities that residues could not be detected except with
+radioactive tracers. Tritium can now be used by health
+officials to study the effects of tranquilizers.</p>
+<div class="pb" id="Page_15">15</div>
+<h2 id="c19">Insects</h2>
+<h3 id="c20">Where and How Fast Do Insects Travel?</h3>
+<p>Radioactive isotopes have been used to study insects,
+their life cycles, dispersion, mating and feeding habits,
+parasites, and predators. Several hundred such studies
+have been made on dozens of insect species.</p>
+<p>With radioactive tracers even the smallest insect becomes
+more easily followed. As one example, nearly half
+a million mosquito larvae were tagged with radioactive
+phosphorus in Canada. Some of the adults from these larvae
+were later found as far as seven miles away, but most were
+recovered within one-eighth mile.</p>
+<p>In a companion study grasshoppers were labeled with the
+same isotope. Their average rate of movement was only
+twenty-one feet per hour, and after seven days their position
+was based entirely on random motions plus prevailing
+winds. It seems that grasshoppers have no ability to move
+toward food.</p>
+<h3 id="c21">How Far Do Insects Carry Pollen?</h3>
+<p>This question is of practical importance in knowing how
+far to separate seed-fields to maintain pure varieties of
+plants. In the past it was studied by the laborious method
+of growing a plant having a dominant &ldquo;marker&rdquo; gene for
+some visible trait surrounded by plants without the marker.
+Seeds from plants at various distances from the marked
+plant were grown the following year to see how far the
+genetically marked pollen had been carried. Since such
+plants are normally cross pollinated, it was difficult to obtain
+strains genetically pure for presence or absence of the
+marker gene. Also, considerable testing and bookkeeping
+were involved.</p>
+<p>With tracers the answer may be found in a few days. A
+plant is injected with radioactive phosphorus; after a few
+days its pollen is highly radioactive. Flowers at various
+distances from the tagged plant may be checked daily for
+radioactivity. In one study with alfalfa, radioactive pollen
+was carried as far as thirty feet by bees, but more than
+<span class="pb" id="Page_16">16</span>
+one-third was deposited on plants adjacent to the labeled
+one.</p>
+<h3 id="c22">Are Predators Used to Destroy Insects?</h3>
+<p>With insect pests, as with plant diseases, biological control
+is more economical than artificial control. The use of
+insecticides too often results in destruction of helpful insects
+along with pests. Limited success has been achieved
+in breeding certain plants for resistance to insects.</p>
+<p>Two important uses of biological control in agriculture
+have been made in recent years: importing an insect from
+Australia to eradicate a weed in California and disseminating
+ladybird beetles to control certain scale insects.</p>
+<p class="caption small" id="fig_5">Fig. 5&mdash;Identifying predators that destroy unwanted insects.</p>
+<div class="img" id="pic_10">
+<img src="images/pag010.jpg" alt="" width="500" height="386" />
+<p class="caption small">Aphids are made radioactive.</p>
+</div>
+<div class="img" id="pic_11">
+<img src="images/pag011.jpg" alt="" width="496" height="315" />
+<p class="caption small">Larger insects found nearby are checked for radioactivity.</p>
+</div>
+<p class="caption small">Bumblebee has not eaten radioactive aphids, but mantis has.</p>
+<p>Helpful parasites and predators must first be identified
+before they can be used. In the case of small or nocturnal
+insects, this can be exceedingly troublesome. Tagging the
+pests with radioisotopes in order to identify the predators
+<span class="pb" id="Page_17">17</span>
+which consume them is much simpler because the most efficient
+predators contain the most activity.</p>
+<p>With such techniques entomologists have studied insects
+and animals which prey on unwanted aphids, mosquitoes,
+blackflies, and roaches. Such experiments may lead to a
+deliberate increase of certain predators to control injurious
+insects.</p>
+<p>Radioactive labeling is also valuable in studying helpful
+insects. In one case the indolence of drone bees was indicated
+by finding that even with adequate syrup in their cage
+they still received identical syrup from worker bees in an
+adjoining cage!</p>
+<h3 id="c23">Can Tracers Measure Spray Residues?</h3>
+<p>Any material used on plants or animals to kill insects or
+disease organisms must pass rigid inspection to be sure it
+does not accumulate in foodstuffs. This is particularly true
+of the &ldquo;systemic&rdquo; poisons, those which are fed to plants via
+leaves or roots and are carried internally to all parts of
+the plant. Such chemicals can be used widely with nonfood
+plants such as cotton to kill insects feeding on them.</p>
+<p>Combining radioactive labeling with other techniques has
+permitted the researchers to show that some compounds
+are soon broken down into harmless chemicals&mdash;a big step
+toward acceptance for their use on food plants.</p>
+<h2 id="c24">Radioisotopes as Radiation Sources</h2>
+<p>Earlier in this booklet radioisotopes were compared to
+fireflies because they emit flashes of &ldquo;light.&rdquo; Isotopes
+serve research in another important way, other than as
+tracers.</p>
+<p>Suppose you collected all the fireflies within a 100-mile
+radius and put them into a glass jar. Instead of an occasional
+twinkle, you would now have a steady glow of light.
+Similarly immense numbers of radioactive atoms can be
+compressed into a small volume to produce steady, intense
+sources of radiation. Agricultural research has answered
+many questions with the use of such radiation sources.</p>
+<div class="pb" id="Page_18">18</div>
+<h3 id="c25">Can Radiation Produce New Plants?</h3>
+<p>Perhaps no biological aspect of atomic energy has so
+caught the fancy of the public as the prospect of creating
+new plant varieties. There is something mysterious about
+pouring invisible energy into seeds or buds and watching
+for changes in the emerging leaves and flowers. There is
+also the challenge of the lottery in being unable to predict
+where, when, or in what form the alterations will appear.</p>
+<p>Although the claims of over-enthusiastic gardeners and
+seed dealers about astonishing new plants &ldquo;created&rdquo; by
+atomic radiation are doubted, clear proof exists even in the
+restrained scientific journals of hereditary changes caused
+by radiation.</p>
+<p>From more than 30 years of scientific study, certain conclusions
+have emerged. High-energy radiations can cause
+sudden hereditary changes (mutations) in any living thing:
+man, animal, microbe, or plant. Any feature of a plant
+subject to hereditary control&mdash;root, shoot, leaf, flower, or
+fruit&mdash;can be altered by radiation. Most of these changes
+are undesirable; they interfere with the normal state of biological
+affairs. A very small percentage of mutated organisms
+is improved in some way. So far changes cannot
+be controlled or predicted.</p>
+<p>To date fourteen new strains of crop plants improved by
+radiation have been put into production in various parts of
+the world. These varieties with their places and dates of
+release follow:</p>
+<dl class="undent"><dt>1. &ldquo;Primex&rdquo; white mustard, Sweden, 1950</dt>
+<dt>2. &ldquo;Chlorina Mutant&rdquo; tobacco, Indonesia, about 1950</dt>
+<dt>3. &ldquo;Shafer&rsquo;s Universal&rdquo; bean, Germany, about 1950</dt>
+<dt>4. &ldquo;Regina II&rdquo; summer oil rape, Sweden, 1953</dt>
+<dt>5. &ldquo;Weibull Stralart&rdquo; fodder pea, Sweden, 1957</dt>
+<dt>6. &ldquo;Sanilac&rdquo; navy bean, Michigan, 1957</dt>
+<dt>7. &ldquo;Pallas&rdquo; barley, Sweden, 1958</dt>
+<dt>8. &ldquo;N. C. 4X&rdquo; peanut, North Carolina, 1959</dt>
+<dt>9. &ldquo;Florad&rdquo; oats, Florida, 1960</dt>
+<dt>10. &ldquo;Seaway&rdquo; bean, Michigan, 1960</dt>
+<dt>11. &ldquo;Alamo-X&rdquo; oats, Texas, 1961</dt>
+<dt>12. &ldquo;Gratiot&rdquo; bean, Michigan, 1963</dt>
+<dt>13. &ldquo;Pennrad&rdquo; barley, Pennsylvania, 1963</dt>
+<dt>14. &ldquo;Yukon-1&rdquo; carnation, Connecticut, 1963</dt></dl>
+<div class="pb" id="Page_19">19</div>
+<p>In these instances no desirable changes appeared in the
+plant grown directly from treated seeds, but they appeared
+several generations later. In most cases hundreds of thousands
+of plants were examined before the desirable ones
+were found. The desired changes were almost always accompanied
+by undesirable ones, and years of cross-breeding
+and &ldquo;purifying&rdquo; were necessary to obtain usable varieties.</p>
+<p>The technique of radiation breeding can be used on any
+form of life where large numbers can be grown and discarded
+at little cost. The output of penicillin has been increased
+a thousandfold by repeated mutations caused in the
+microorganism producing this antibiotic. Several studies on
+radiation breeding of poultry have been started.</p>
+<p>An ingenious reverse twist of induced mutation is being
+applied in the field of plant diseases. While some scientists
+are irradiating seeds and plants in an effort to obtain
+disease-resistant mutations, others are irradiating the
+fungi which cause the diseases. They hope in this way to
+foresee the new strains of pathogenic microbes that will
+occur naturally in order to breed resistant plants before
+the new diseases appear.</p>
+<p>Some claims have been made that radiation can stimulate
+plant growth, germination, earlier maturity, and so on.
+Similar benefits are sometimes claimed for human health.
+These allegations are almost never proved in reputable
+laboratories. It seems likely that radiation is stimulating,
+in the words of one authority, &ldquo;only in the sense that a
+pruning knife is stimulating.&rdquo;</p>
+<h3 id="c26">Can Radiation Destroy Germs and Insects?</h3>
+<p>Food technologists have studied ways of preserving food
+with radiation for more than ten years. Their findings indicate
+that complete sterilization of food with radiation requires
+doses so high (2 to 6 million roentgens<a class="fn" id="fr_2" href="#fn_2">[2]</a>) that cost
+<span class="pb" id="Page_20">20</span>
+is prohibitive at present, and the food often becomes distasteful.
+These amounts of energy completely destroy the
+microbes and enzymes which normally cause food to putrefy.</p>
+<p>If radiation is to be used in preserving food, it will probably
+be as a supplement to conventional methods of heating
+and freezing. &ldquo;Pasteurizing&rdquo; with radiation to destroy most
+(but not all) of the microbes in meat or fruit or vegetables
+is accomplished with less than five per cent of the dosage
+required for sterilizing. Such treatment does not alter
+flavor or texture appreciably and could be used to prolong
+the refrigerated &ldquo;life&rdquo; of many fresh foods. It is the responsibility
+of the Federal Food and Drug Administration
+to determine that no threat to human welfare could possibly
+result before approving the use of high-energy radiation to
+preserve foods.</p>
+<p>With agricultural products stored dry, such as grain,
+tobacco, and wool, the chief agents of damage are not microbes,
+but insects. The loss of stored field crops caused
+by insects is estimated at $200 million annually in the
+United States. Deinfesting such goods with radiation doses
+in the &ldquo;pasteurizing&rdquo; range promises to be practical and
+causes no apparent change in the product.</p>
+<p>Like many other foodstuffs, potatoes are often stored for
+months between harvest and use. Precaution must be taken
+to prevent their deterioration during storage not only from
+decay but also from sprouting.</p>
+<p>Cold storage inhibits sprouting but is costly and has another
+serious drawback. In the making of potato chips,
+tubers held at low temperature contain excess sugar and
+result in darkened chips. Storage at higher temperatures
+prevents conversion of starch to sugar but encourages
+sprouting.</p>
+<p>Atomic energy promises to resolve this dilemma. Given
+low doses of gamma rays (5000 to 10,000 roentgens), potatoes
+may be kept at room temperature for a year or more
+without sprouting. Similar doses inhibit sprouting of onions.
+The estimated cost of irradiating tubers and bulbs at such
+doses is as low as 14 cents per ton. No chemical changes
+have yet been found in irradiated potatoes that would make
+them unsafe for eating. In fact, health officials in Canada
+<span class="pb" id="Page_21">21</span>
+have recently approved the use of gamma rays on potato
+tubers that will be stored and later used for human food.
+Our own Food and Drug Administration has given similar
+approval for applying gamma rays to bacon and fast electrons
+to wheat (for killing insects).</p>
+<p>An ingenious application of atomic energy to agriculture
+concerns the screwworm fly, which inhabits large areas of
+southern United States, Mexico, and the Caribbean. The fly
+lays eggs in open wounds of livestock, including navels of
+newly born, and the burrowing maggots inevitably kill the
+animal. In the southeastern United States, damage from this
+insect amounted to $15 to $25 million annually.</p>
+<p>In the years 1958 and 1959 more than two billion screwworm
+flies were deliberately released from airplanes over
+the entire state of Florida and parts of Georgia and Alabama.
+This astonishing act was a major step in successful
+eradication of the pest from southeastern United States.</p>
+<p>The entomologists who conceived this remarkable scheme
+had the following information from basic studies: the insect
+produces a generation about every three weeks. In the
+pupal stage males can be sterilized by 2500 roentgens of
+X or gamma rays, females by 5000 roentgens. The insect
+can be reared in large numbers. Sterile males are fully
+competitive with normal males for mates. And, of course,
+sterile eggs do not hatch. (It was helpful, though incidental,
+that females mate only once.)</p>
+<p>After initial tests on an island in the Caribbean, a large
+fly-producing plant was set up. Flies were grown to the
+pupal stage, irradiated with 8000 roentgens of gamma rays,
+permitted to mature, and released from airplanes. With
+50 million flies being released weekly over Florida, Georgia,
+and Alabama, the area was smothered with sterile
+flies, and the number of eggs that hatched (from the normal
+native flies) rapidly diminished to zero. The program was
+continued for 18 months, and in this time the insect was
+completely eliminated.</p>
+<p>Certain other insects are being considered for the
+sterility-eradication technique. Among them are the boll
+weevil, European corn borer, mosquito, and tsetse fly.
+Oriental scientists are using gamma rays instead of the
+conventional heating to kill silkworms inside cocoons.</p>
+<div class="pb" id="Page_22">22</div>
+<h3 id="c27">How Does Radiation Affect Farm Animals?</h3>
+<p>At a few colleges of agriculture in this country, radiation
+effects on farm animals are being studied.</p>
+<p>Although it may not be flattering to be likened to a pig or
+a donkey, the fact remains that human beings are physiologically
+very similar to swine and burros. These animals
+are mammals with simple stomachs and have the same
+general size, shape, and placement of organs as do humans.
+Radiation studies with swine and burros, although slow and
+expensive, should give information more applicable to humans
+than the more rapid and inexpensive studies with
+small laboratory animals.</p>
+<h3 id="c28">What Else Can Radiation Tell Us?</h3>
+<p>Two characteristics of soils besides fertility are vitally
+important and difficult to measure. These characteristics
+are moisture and density. Moisture must be determined
+frequently for efficient irrigation. Density controls the pore
+space available for water and oxygen; the possible damage
+to the soil from tillage and harvesting machines is revealed
+by before-and-after tests of density.</p>
+<p>Both soil moisture and density were formerly determined
+by laboratory methods, which had two drawbacks: the methods
+were laborious, and they tested soil in an unnatural
+state. Today a sort of double-barreled radiation method
+can be used to measure these two soil characteristics.</p>
+<p>Neutrons are readily scattered by water but not by soil;
+gamma rays are absorbed by both soil and water. In practice
+the experimenter drills two holes in the soil a few feet
+apart. Into one he puts a gamma-ray source; into the other,
+a radiation detector. The reading on his detector dial tells
+him the amount of gamma rays absorbed by both soil and
+water. Replacing the gamma-ray source with a neutron
+source, he obtains a reading on absorption by water only.
+The difference between the two readings is ascribed to the
+density, or degree of compaction, of that soil in its native
+state.</p>
+<div class="pb" id="Page_23">23</div>
+<h2 id="c29">Conclusion</h2>
+<p>Radioactive tracers and radiation sources have become
+indispensable to all phases of agricultural research. They
+have helped answer questions that seemed unanswerable.
+But there will always be more questions to put to Nature.
+The physicists-philosophers of 1890 were confident that
+they had obtained all significant knowledge of the physical
+universe. Discoveries of the next twenty years revealed
+the immaturity of that conviction.</p>
+<p>The modern poet Archibald MacLeish has dramatized the
+meagerness of knowledge:<a class="fn" id="fr_3" href="#fn_3">[3]</a></p>
+<div class="verse">
+<p class="t0">I will tell you all we have learned ...</p>
+<p class="t">the lights in the sky are stars</p>
+<p class="t0">We think they do not see</p>
+<p class="t">we think also</p>
+<p class="t0">The trees do not know nor the leaves of the grasses hear us....</p>
+</div>
+<p>Perhaps the most characteristic realization of the scientist
+today is that the universe is too complex to be fully
+described, that concepts must change repeatedly to absorb
+new findings, and that the recurring miracle of life is more
+majestic than any formula, any computer, or any rocket
+that man&rsquo;s brain can devise.</p>
+<div class="pb" id="Page_24">24</div>
+<h2 id="c30">Suggested References</h2>
+<p class="book"><i>Applications of Radioisotopes and Radiation in the Life Sciences.</i>
+Hearings before the Subcommittee on Research,
+Development and Radiation of the Joint Committee on
+Atomic Energy, Congress of the United States, March 27-30,
+1961. Superintendent of Documents, U. S. Government
+Printing Office, Washington 25, D. C. 1961, 513 pages,
+$1.50.</p>
+<p class="book"><i>Experiments with Radiation on Seeds.</i> Thomas S. Osborne.
+U. S. Atomic Energy Commission, Division of Technical
+Information Extension, Oak Ridge, Tenn. No. 1, 11 pages;
+No. 2, 30 pages, free.</p>
+<p class="book"><i>Oklahoma Conference&mdash;Radioisotopes in Agriculture.</i>
+(Proceedings of a conference held at Oklahoma State University,
+April 2 and 3, 1959.) TID-7578. Superintendent
+of Documents, U. S. Government Printing Office, Washington
+25, D. C. 1959, 287 pages, $2.00.</p>
+<p class="book"><i>Radioactive Isotopes in Agriculture.</i> (Proceedings of a conference
+held at Michigan State University, January 12-14,
+1956.) TID-7512. Superintendent of Documents, U. S.
+Government Printing Office, Washington 25, D. C. 1956,
+416 pages, $3.00.</p>
+<p class="book"><i>Radioisotopes in Science and Industry.</i> U. S. Atomic Energy
+Commission. Superintendent of Documents, U. S. Government
+Printing Office, Washington 25, D. C. 1960, 176
+pages, $1.25.</p>
+<p class="book"><i>What Can You Expect from Atomic-Irradiated Seeds?</i>
+James L. Brewbaker. U. S. Atomic Energy Commission,
+Division of Technical Information Extension, Oak Ridge,
+Tenn. Not dated, 8 pages, free.</p>
+<h3 id="c31">Motion Picture</h3>
+<p>(Available for loan without charge from the Division of
+Public Information, U. S. Atomic Energy Commission,
+Washington 25, D. C.)</p>
+<p class="book"><i>Harvest of an Atomic Age</i>, 20 minutes, 16mm, color and
+sound, 1963.</p>
+<h2 id="c32">Footnotes</h2>
+<div class="fnblock"><div class="fndef"><a class="fn"  id="fn_1" href="#fr_1">[1]</a>A microgram bears the same relationship to a 1000-pound
+steer as a penny does to $4&frac12; billion.
+</div><div class="fndef"><a class="fn"  id="fn_2" href="#fr_2">[2]</a>The roentgen is a measure of ionizing radiation, as the foot-candle
+is a measure of light. In simple terms the roentgen is that
+amount of X or gamma radiation which produces one electrostatic
+unit (esu) of electricity in one cubic centimeter (cc) of dry air at
+standard conditions of temperature and pressure. This may sound
+like a trivial amount of energy, but it amounts to more than two
+billion ionizations in each cubic centimeter.
+</div><div class="fndef"><a class="fn"  id="fn_3" href="#fr_3">[3]</a>From &ldquo;Epistle To Be Left in the Earth.&rdquo;
+</div>
+</div>
+<h2 id="c33">Transcriber&rsquo;s Notes</h2>
+<ul><li>Retained publication information from the printed edition: this eBook is public-domain in the country of publication.</li>
+<li>Where possible, UTF superscript and subscript numbers are used; some e-reader fonts may not support these characters.</li>
+<li>In the text version only, underlined or italicized text is delimited by _underscores_.</li>
+<li>In the text version only, superscript text is preceded by caret and delimited by ^{brackets}.</li>
+<li>In the text version only, subscripted text is preceded by underscore and delimited by _{brackets}.</li>
+<li>In the text version only, added a brief label to each illustration; and for graphs, provided tabular summaries of the data where possible.</li></ul>
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of Project Gutenberg's Atoms in Agriculture, by Thomas S. Osborne
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+</pre>
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+</body>
+</html>
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author	nfenwick <nfenwick@pglaf.org>	2025-02-22 01:03:40 -0800
committer	nfenwick <nfenwick@pglaf.org>	2025-02-22 01:03:40 -0800
commit	ae0a130e9c3dc560dfd4729c19c9dfa402e8c872 (patch)
tree	8ed66c671a54e26a797cbb0fe87cc90f280209f3