4. The Potash Supply : 



(a) The percentage of potash in a potato fertilizer should be rel- 

 atively high. There is considerable evidence which tends to show 

 that a relatively high percentage of potash in the fertilizer used for 

 potatoes is favorable to the maintenance of healthy growth and the 

 production of a sound crop. 



(b) The potash of a potato fertilizer should usually be supplied 

 in the form of sulfate rather than muriate. When these two salts 

 have been compared, the sulfate has generally given the heavier 

 yields and the better quality. On light soils, especially those rich in 

 lime and in excessively dry seasons, the muriate may be the better of 

 the two salts. 



The Use of Lime and Wood Ashes : It has been clearly shown 

 that potatoes are more subject to scab when grown in soils which 

 are alkaline than in those which are moderately sour. The free 

 application of lime will render most soils alkaline and this fact 

 explains why the potato is so often seriously injured by scab when 

 grown on freshly limed land. This practice should be avoided. A 

 heavy application of wood ashes may have a similar effect in favor- 

 ing the development of scab and it is usually preferable to derive the 

 phosphoric acid and the potash needed for the potato from other 

 fertilizers. 



The Composition of Potato Fertilizers : It is believed that fer- 

 tilizers for potatoes should under the different conditions specified 

 have about the following composition : 



A. When fertilizers only are to be used : — 



1. On clover sod or soils rich in humus and relatively fertile : 



Per Cent. 



Nitrogen, 2.5 — 3. 



Phosphoric acid, 8. — -10. 



Potash, 8. — 10. in form of sulfate. 



2. On lighter and poorer soils : 



Per Cent. 



Nitrogen, 3.5— 4.5 



Phosphoric acid, 6. — 8. 



Potash, 8. — 10. 



B. For use in connection with manure : 



I. On clover sod or soils rich in humus: 



Per Cent. 



Nitrogen, 1.5 — 2. mostly in soluble forms. 



Phosphoric acid, 8. — 10. 



Potash, 12. — 14. 



