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:

Other questions arise in agricultural research:

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?