WATER-CULTURE METHOD — HOAGLAND AND ARNON 477 



greenhouse crops of many species in winter months no matter what 

 nutrient conditions are present in the culture solution. 



NUTRIENT REQUIREMENTS OF DIFFERENT KINDS OF PLANTS 



The question is frequently asked: Does each kind of plant require 

 a different kind of nutrient solution? The answer is that if proper 

 measures are taken to provide an adequate supply of nutrient ele- 

 ments, then many kinds of plants can be grown successfully in nutrient 

 solutions of the same initial composition (the same fertile soil can 

 produce high yields of many kinds of plants). 



The composition of the nutrient solution should always be con- 

 sidered in relation to the total supply as well as the proportions of 

 the various nutrient elements. To give a specific illustration: assume 

 that several investigators prepare nutrient solutions of the same 

 formula, but one uses 1 gallon of the solution for growing a certain 

 number of plants, another 5 gallons of solution, and still another 50 

 gallons of solution. If plants were grown to large size, each investi- 

 gator would reach a different conclusion as to the adequacy of the 

 nutrient solution employed, although the initial composition was the 

 same in all cases. The investigator using the small volume might 

 find that his plants became starved for certain nutrients, while the 

 one using the larger volume experienced no such difficulty. In fact, 

 the precise initial composition of a culture solution has very little 

 significance, since the composition undergoes continuous change as 

 the plant grows and absorbs nutrients, and the rate and nature of this 

 change depends on many factors, including total supply of nutrients. 

 Adequacy of supply of nutrients involves volume of solution in rela- 

 tion to the number of plants grown, stage of growth of the plant and 

 rate of absorption of nutrients, and frequency of changes of solution. 



Apart from the question of adequate supply of nutrients, there are 

 certain special responses of different species of plants which have to 

 be taken into account in the management of nutrient solutions. 

 Plants vary in their tolerance to acidity and alkalinity. They also 

 differ in their susceptibility to injury from excessive concentrations 

 of elements like boroD, manganese, copper, and zinc. Some plants 

 may be especially prone to yellowing because of difficulty in absorb- 

 ing enough iron or manganese. Some may succeed best in more 

 dilute nutrient solution than is employed for most kinds of plants. 

 Unfavorable responses by certain plants to high nitrogen supply, in 

 relation to fruiting, under certain climatic conditions, may require 

 consideration. 



Since the adaptation of a nutrient solution to the growth of any 

 particular kind of plant depends on the supply of nutrients and on 

 climatic conditions, there is no possibility of prescribing a list of 



