A MEMORANDUM 

 REGARDING NOMENCLATURE 



hy Daniel I. Arnon, Ph.D. 



Division of Plant Nutrition, University of California, Berkeley, California 



In the EngHsh-speaking countries elements required by plants 

 in minute quantity are often called "trace," "minor" or "rare" ele- 

 ments. While these terms have acquired a more or less definite 

 meaning among plant physiologists, there has been a recent tend- 

 ency among workers in the field of soil and fertilizers to extend 

 these terms to cover all inorganic elements derived by the plapt 

 from the soil, except for the three "major" fertilizer elements, 

 nitrogen, phosphorus and potassium. 



In recent years sentiment has been crystallizing in America to 

 designate elements required by plants in minute quantity by the 

 term "inorganic micronutrients" or "micronutrients" for short, 

 when the context precludes confusion with organic micronutri- 

 ents. The term micronutrients describes manganese, copper, bo- 

 ron, zinc and molybdenum. It is suggested that, disregarding 

 historical reasons, it should also include iron, which is required 

 by plants in small amounts. The analogous term "macronutri- 

 ents" would then describe the six inorganic nutrients derived 

 from soil and absorbed by plants in large amounts : potassium, cal- 

 cium, magnesium, nitrogen, phosphorus and sulphur. 



The objections to the terms "rare," "trace" and "minor" ele- 

 ments can be stated as follows. They are not "rare" either in the 

 plant or in the soil. They are not "minor" in the sense that a 

 deficiency of them would be of less consequence to the plant than 

 a deficiency of a "major" element. They are not "trace" elements 

 in the sense that their presence can be detected but their content 

 is too small to measure. On the contrary, the current trend in 

 research in this field is notable for the quantitative determination 

 of these elements within the plant as well as in the nutrient 

 medium. 



It is submitted that the adoption of the term "micronutrients" 

 in the English-speaking countries would further clarity of thought 

 and implication, and be a distinct aid in teaching. This proposal 

 is limited to English terminology and does not bear on well serv- 

 ing analogues in other languages. 



