Lecture 7 



— 159 



Potassium Nutrition 



and OVERSTREET* in this laboratory. In this experi- 

 ment potassium behavior was reflected by the element 

 rubidium, which can be obtained in suitable long-lived 

 radioactive form. There is every reason to believe 

 that for the purpose in view rubidium presents a 



I5Q 300 430 600 750 900 1050 1200 1350 

 K IN RRM. DRY SOIL 



O WATER SOLUBLE K AGAINST ADDITIONS K TO SOILS A AND B 

 • WATER SOLUBLE K AGAINST REPLACEABLE K IN SOILS A AND B 



Textfigure 42, — Showing increases in soil solution K (as 

 reflected in water soluble K) with increasing additions of K 

 salt to the soil and concomitant increases in replaceable K. The 

 larger part of the added K may be fixed on solid phases of the 

 soil, in soils of this character, and not appear in the soil 

 solution. (HoAGLAND and Martin, 1933). 



behavior analogous to that of potassium. Radioactive 

 rubidium was added to the soil under study and then 

 the soil was leached with a calcium salt so as to remove 

 all the rubidium present in easily replaceable form, 

 leaving a considerable portion of the rubidium, which 

 had been fixed in non-replaceable, or difficultly re- 

 placeable, form. Subsequently barley plants were 

 grown in the leached soil. They absorbed significant 

 amounts of rubidium. Since the rubidium was tagged 



•Private communication. 



