Deficiency Symptoms

The simplest and in many respects the most satisfactory method for ascertaining the need for certain nutrients is to recognize deficiency symptoms by the color of the foliage, the size of the plants, and their growth habit.

A light-green or yellowish color of corn plants indicates to every farmer the lack of nitrogen in the plant. Symptoms of nitrogen deficiency may be temporary on cold, wet soils and may disappear in early summer under more favorable soil conditions. Color charts are now being used by growers to measure the color of the leaves of apple trees. It serves as a fairly dependable method for ascertaining the nitrogen requirements of apple trees. No doubt this procedure could be used to advantage with many other crops.

Symptoms of deficiencies of other nutrients, like potash, magnesium, manganese, and boron, are now well established. Phosphorus deficiency remains one of the most difficult to recognize. Excellent descriptions of commonly occurring deficiency symptoms in the important crops ,have been published in Hunger Signs in Crops. It should be pointed out, however, that an accurate diagnosis by means of deficiency symptoms requires considerable experience and close observation. Faulty diagnosis is not at all uncommon. For instance, the chlorotic leaf margins of alfalfa caused by leaf hopper injury are easily mistaken for boron deficiency. It also is difficult to distinguish between the symptoms of magnesium and manganese deficiency. Nevertheless, when used by an experienced observer, diagnosis by means of deficiency symptoms is one of the most useful methods of determining the fertilizer needs of crops.

Thus soil tests, plant-tissue tests, and deficiency symptoms are useful for identifying nutritional disorders in crops. Each technique has its limitations, it is true; but when properly used, especially in conjunction with each other, they can be of help as guides to fertilizer recommendations and for finding out why crops fail.

THE AUTHORS

Michael Peech is professor of soil science at Cornell University, Ithaca, N. Y. A native of Canada, he was graduated from the University of Saskatchewan in 1930 and completed his graduate studies in soil chemistry at Ohio State University. Since 1933 he has been doing research in and teaching soil chemistry at several colleges and State agricultural experiment stations. Dr. Peech has made extensive investigations of the chemical properties of soils in relation to their inherent fertility and response to fertilizers, particularly in an effort to develop rapid chemical soil tests for determining the fertilizer needs of soils.

Hans Platenius is associate professor of vegetable crops at Cornell University, Ithaca, N. Y. He had his early training in agricultural chemistry in Germany and later continued his graduate work in plant sciences and biochemistry at the University of Nebraska and at Cornell. As a member of the research staff in the department of vegetable crops at Cornell University, Dr. Platenius has spent much time in recent years making a systematic study of the value of chemical analysis of plants for diagnosing deficiencies of nutrient elements in vegetable crops.