Hoagland —164— Plant Nutrition 



is true that phosphate and other nutrients are also 

 mobilized in the fruit and that large amounts of sugar 

 or other organic compounds are transported in this 

 direction. The symptoms of injury to the plant sug- 

 gest, however, even though they may not conclusively 

 prove, that potassium is the critical determinant. 



Somewhat analogous results have been obtained 

 with heavily fruiting tomato plants grown in a green- 

 house in Berkeley. Here, in aerated culture solutions 

 it is possible to prevent almost entirely symptoms of 

 potassium deficiency, despite very heavy fruiting, by 

 maintaining suitably high concentrations of potassium 

 in the well aerated nutrient solution. Frequently the 

 prune trees have not been maintained in health, even 

 when so much potassium was added to the soil, at 

 suitable depths, that the foliage content of potassium 

 early in the summer was raised to a high percentage. 



The development of a heavy crop reduces markedly 

 the potassium content of the foliage early in the fall. 

 Whether the relation is direct or indirect, the exces- 

 sive migration of potassium is accompanied by dieback 

 injury. I have been speaking of extreme cases. There 

 are conditions under which leaf scorch and similar 

 injury to fruit trees can be corrected by practical 

 applications of potash fertilizers to the soil. 



Interrelations of Bases in Absorption and the Role 

 of Potassium in Plant Sap Buffer Systems : — The ab- 

 sorption of potassium by roots is related to the absorp- 

 tion of other ions as well as to the chemical nature 

 of potassium compounds in the soil. This is another 

 physiological aspect of the problem. Of particular 

 interest is the interrelationship in absorption of potas- 

 sium, calcium and magnesium. Manifold researches 

 have shown that the alteration of a soil or of a culture 

 solution medium so as to promote the absorption of 

 potassium will in general tend to decrease the absorp- 

 tion of calcium and magnesium, especially on the basis 

 of the amounts of these elements absorbed per unit 



