32 



SOIL CONDITIONS AND PLANT GROWTH 



there is a corresponding shortage in the yield. The yield 

 rises if some of the lacking factor is added, and goes up all the 

 further the lower it had previously fallen. Mitscherlich put 

 this as follows : the increase of crop produced by unit incre- 

 ment of the lacking factor is proportional to the decrement 



100 



Lo^ (94'6-y)- 1,9615- I ^^v/x 2 



10 25 50 100 



Calcium Monophosphate. 



Fig. 2. — Mitscherlich's curve showing relation between yield of oats and amount 

 of phosphate supplied. 



from the maximum. The advantages of this form is that it 

 can be expressed mathematically : — 



^= (A - y)k or log,(A -y=^)c-kx, 



where,;/ is the yield obtained when ^ = the amount of the 



