34 THE POTATO 



The time and method of application must be con- 

 sidered. In my experience muriate of potash has given 

 better resuhs when applied the previous fall, especially 

 if more than loo pounds per acre are to be applied, the 

 presumption being that the potassium compound under- 

 goes changes in the soil, and that the injurious chlorine 

 is removed as a chloride by the winter and spring 

 rains. For spring application in the drills sulphate of 

 potash may be better, or a mixture of sulphate and mu- 

 riate of potash, if more than the above-mentioned 

 quantity is required. The disadv^antage of the muriate 

 of potash seems to be due to the fact that it is a chlo- 

 ride, and Sjollema ' and Pfeiffer * have shown that the 

 chlorides of potassium, sodium (common salt) , and mag- 

 nesium, when added to the sulphate of potash, dimin- 

 ished the starch content of the potatoes considerably, 

 and that the redudtion was greatest in varieties rich 

 in starch. This would seem to support the common 

 idea that sulphate of potash produces better quality 

 potatoes than muriate of potash. Wheeler,' of Rhode 

 Island, shows that calcium chloride had a marked 

 poisonous effect upon potatoes and nearly destroyed 

 them, while the same amount of calcium in certain 

 forms other than the chloride or sulphate increased the 

 yield and vigor of the plants. New varieties, and 

 those making a heavy growth of haulm, seem to be 

 particularly sensitive to chlorides. 



Influence of Phosphoric Acid. — Lack of phos- 

 phoric acid is accompanied by dark green leaves. While 

 phosphoric acid aids starch formation, it is often re- 



> E. S. R., XII., 434- * K. S. R., XII.. 443- * R- I- Bui. 40, pp. 85. 86. 



