Frontiers of Science:

The Incredible Flying Plant Doctor

By Dr. Sherwood B. Idso

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    What is the first thing doctors or nurses do when you are sick? They take your temperature, right? Well, would you believe that scientists are now doing the same thing with plants? It’s true. In many agricultural research centers throughout the world, a quiet revolution is taking place. Space-age technology is being applied to growing crops; and one of the most promising techniques under study is the measurement of plant temperatures to detect water shortages, diseases, and their harmful effects on plant growth.

    The instrument that makes these temperature measurements possible is the infrared thermometer. It is one of a number of instruments that works by the principle of remote sensing—making temperature measurement without having to touch the object being measured. The reason it can do this is that all objects give off heat radiation that travels through air and space like light; and the hotter the object is, the more heat radiation it gives off. Thus, by sensing some of this invisible heat energy, an infrared thermometer can be used to determine the temperature of the object.

    Now one of the most important requirements for good plant growth is that there be plenty of water available to the plant roots. When this is the case, water is easily taken up from the soil by the roots and carried to the leaves. There it evaporates to cool the plant, just like you are cooled when coming up out of the water after a swim. If there is not enough water in the soil for good plant growth, however, not as much water will be evaporated from the plant leaves and they will become slightly warmer. By merely pointing an infrared thermometer at the plants, you can quickly tell if they have enough water or if they are in need of more. If they are “running a fever,” a remedy is required, and where irrigation is practiced, more water is quickly prescribed.

    In addition to running out of moisture in the soil, there are many other reasons for plants to run a fever. Many plant diseases, for instance, attack plant roots and reduce their ability to extract water from the soil. Still other diseases—and sometimes even insect pests—interfere with the plant’s ability to transfer water from the roots to the leaves. The final result is the same in all cases: less evaporation of water from the leaves and higher plant temperatures.

    As research in this area is progressing, hand-held infrared thermometers that look a lot like futuristic ray guns are becoming available to individual farmers who want a reliable tool for scheduling irrigation. On a much larger scale, aircraft that could serve whole groups of farmers are being used in experimental tests of similar equipment that can take actual temperature “pictures” of the fields they fly over. Earth-orbiting satellites are surveying even larger areas of the globe in much the same way. Scientists hope that the information they obtain in these ways can be used to more wisely manage our precious water resources and to provide an early warning of impending agricultural disasters and a means for predicting crop yields. If they are successful, the production and distribution of food throughout the world could be greatly improved, helping to reduce much malnutrition and starvation. Thus, the work of the plant doctor goes a long way toward helping people too.

    Illustrated by Dick Brown

    Photography by Sherwood B. Idso

    1 Minutes before sunrise a scientist spot-checks the temperature of a wheat crop, while an airplane above him maps out the temperature of each square foot of the entire field.

    2 peering through a canopy of cotton leaves that have been severely damaged by insects, a scientist checks the surface soil temperature to see if further insect development is to be expected and if more insecticides will be needed.

    3 A scientist at the U.S. Water Conservation Laboratory in Phoenix, Arizona, takes aim at a cotton crop with an infrared thermometer. If plants show signs of heat stress (4), they are irrigated.

    5 About 2 P.M. in the afternoon, an aircraft flies over a group of experimental wheat plots, obtaining a temperature picture of its six different sections.

    6 The black, purple, and blue colors represent temperatures cooler than air, while the yellow and orange colors represent temperatures warmer than air, with black the coldest and orange the warmest. Four of the plots appear to be fairly cool and well watered, while one of them is very warm and stressed and another is just reaching the stage where it should be irrigated. (NASA photo.)

    7 Artist’s conception of an experimental satellite that has been used to obtain temperature maps of large sections of the earth from its orbit in space. (NASA artwork.)