EXHAUSTION OF POTASH 



lit 



potash. The results in later years show, however, that neitlicr 

 magnesia nor soda can rephice potasli, tlieir good effect in tlic 

 first few years being due to the fact tliat tlie addition of aiiv 



Bushels 

 per Acre. 



30 



10 



1852-61 1862-71 1872-81 1882-91 1892-1901 



Fig. i3. — Production of Wheat with varyinijc MintTal Maiitiros. All Plots receive finally 

 86 lb. N. as Ammonium-salts. Averages over 10-year periods (18.52-1901). 



soluble salts to the soil brings into action some of the dormant 

 potash. At first this is sufficient to grow as large a crop as 

 where a potash manure is directly supplied, Init in course of 

 time the available potash becomes exhausted, and tht'ie is a 

 manifest decline on the plots receiving magnesia or soda only. 

 Plot 7, which differs only from Plot 13 in receiving magnesia 

 and soda in addition to the potash, phosphoric acid, and nitro- 

 gen applied to 13, gives throughout a .somewliat higher (ro|>. 

 This is not due to any specific effect of magnesia and soda, 

 because Plot 13 does not show any progressive decline as com- 



