EXPERIMENTAL METHODS FOR THE STUDY OF THE ROLE OF COPPER, MANGANESE, AND ZINC IN THE NUTRITION OF HIGHER PLANTS

Abstract

IN INVESTIGATING the role of zinc, manganese, and copper in plant nutrition, the use of suitable experimental methods for growing plants assumes particular importance. The amounts of these socalled microelements required by plants are so small that they are frequently supplied in considerable part or in toto by the incidental impurities included in the culture medium. A successful demonstration of the indispensability, as well as any study of the quantitative aspects of the importance of microelements in the nutrition of higher plants, depends directly on the removal of contaminants from the culture medium. The purpose of this investigation was to develop an experimental technique which, with the use of ordinary laboratory and greenhouse facilities, would permit the undertaking, on a fairly large scale, of experiments to study the physiological importance of zinc, manganese, and copper in the nutrition of higher plants. The object was attained by using the water culture method and, by proper selection of materials and purification procedures, reducing the contaminations derived from water, chemicals, and containers. The use of very sensitive chemical tests to determine the amounts of contaminants present in the culture medium after purification made it possible to prepare nutrient solutions of equal degrees of purity. It was possible, using this technique, to obtain consistent and reproducible responses in plants from adding minute amounts of metals to the nutrient medium (for example, 1 part of zinc in 200,000,000 parts of culture solution, which amounted to 1 y [0.001 mg.] of zinc to a plant). GENERAL CONSIDERATIONS.-The metal contaminants found in nutrient solutions are derived from three sources: containers, water, and chemicals. Previous investigators (Steinberg, 1919, 1935; Hopkins, 1933), studying the effect of microelements on lower plants, have described successful methods for nutrient solution purification in which metal impurities were removed by precipitation and adsorption at high temperatures and slightly alkaline reactions in the presence of calcium and phosphate ions. They have applied these purification procedures to either the complete nutrient solution (Steinberg, 1919, 1935) or to one divided into two portions (Hopkins, 1933), removing in one or two operations such impurities as were derived from the several nutrient compounds, water, and containers.2