CHAPTER I 

 PLANT NUTRIENTS 



THERE is some confusion in the use of the terms "nutrient," 

 " plant food," etc., as applied to the nutrition and growth of 

 plants. Strictly speaking, these terms ought probably to be lim- 

 ited in then* application to the organized compounds within the 

 plant which it uses as sources of energy and of metabolizable 

 material for the development of new cells and organs during its 

 growth. Botanists quite commonly use the terms in this way. 

 But students of the problems involved in the relation of soil 

 elements to the growth of plants, including such practical ques- 

 tions as are involved hi the maintenance of soil productivity 

 and the use of commercial fertilizers for the growing of economic 

 plants, or crops, are accustomed to use the terms " plant foods," 

 or " mineral nutrients," to designate the chemical elements and 

 simple gaseous compounds which are supplied to the plant as the 

 raw material from which its food and tissue-building materials 

 are synthetized. Common usage limits these terms to the soil 

 elements; but there is no logical reason for segregating the raw 

 materials derived from the soil from those derived from the atmos- 

 phere. 



The essential difference between these raw materials for plant 

 syntheses and the organic compounds which are produced within 

 the plants and used by them, and by animals, as food, is that the 

 former are inorganic and can furnish only materials but no energy 

 to the organism; while the latter are organic and supply both 

 materials and potential energy. It would probably be the best 

 practice to confine the use of the word " food " to materials of the 

 latter type, and several attempts have been made to limit its use 



