SOIL CONDITIONS AFFECTING PLANT GROWTH 31 



was grown in pots of sand, all necessary factors were amply 

 provided, excepting only potassium salts, the amount of which 

 varied in the different pots. The weights of dry matter formed 

 are shown in Table IV. 



Table IV. — Effect of Potassium Salts on Growth of Barley 

 Hellriegel (i3o<i). 



These results are plotted in Fig. i 



CO 



a 



ISO 



25 

 o 



o 

 a.15 



%• 



a 

 S 5 



25-5 47 70-5 94 



28? 



Fig. 



KCl. used (MgmsKzO.) 



-Relation between potash supply and growth of barley (Hellriegel). 



Similar curves are obtained when the varying nutrient is 

 nitrogen or phosphorus. 



The smoothness of the curve suggests that it can be ex- 

 pressed by a mathematical equation, and E. A. Mitscherlich 

 has attempted to do this, proceeding in the following manner : 

 If all the conditions were ideal, a certain maximum yield would 

 be obtained, but in so far as any essential factor is deficient 



