Hoagland _110— Plant Nutrition 



may be greatly influenced by the so-called luxury ab- 

 sorption of certain elements — that is, the absorption 

 of increments of an element that do not produce any 

 increase in weight of the plant, and this luxury ab- 

 sorption is dependent in part on solution composition. 

 These general statements are not intended to discount 

 the possibility that in special cases ionic relations may 

 require careful adjustment. Shive has pointed out 

 the importance of an interrelation between concentra- 

 tions of iron and manganese in culture solutions, aside 

 from the provision of an adequate total supply of 

 these nutrients. Even so, no exact ratio is imperative. 



The question of plant composition in relation to 

 the nutrient solution is extremely complex. Ionic inter- 

 relations in absorption are important. Some of them 

 are easily demonstrable even in dilute solutions when 

 solutions are varied considerably in composition. As 

 an illustration, with a given concentration range for 

 calcium and magnesium in a nutrient solution, an 

 increasing concentration of potassium will usually de- 

 crease absorption of these ions, per unit of plant 

 growth, and so influence the percentage composition 

 of the plant with reference to potassium, calcium and 

 magnesium, a question to be discussed more fully in 

 another lecture. Reciprocal relations between phos- 

 phate and nitrate ions have frequently been reported 

 and have been met with in our own experiments. 

 COLLANDER (1941) suggests that some ions closely 

 related chemically act almost like isotopes in their 

 absorption inter-relations. The complexities already 

 mentioned are greatly augmented through the differ- 

 ential behavior of different species of plants growing 

 in the same nutrient environment. Collander's recent 

 investigation gives some of the best evidence of this 

 differential selective uptake of ions by plants of dif- 

 ferent species, growing in the same nutrient solution. 



There is another concept which may be employed 

 in the selection of salt proportions for a nutrient 



