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.