320 The Potato Crops 



ment Station : " Well decomposed stable manure applied 

 in the row is beneiicial in producing maximum yields, but 

 when manure is used in the drill, the surface of the sweet 

 potato is more likely to be disfigured with black marks 

 known as scurf, and spoken of as ' soil stain,' ' mottling,' 

 'rust,' etc. This spoils the appearance of the sweet pota- 

 toes and reduces their keeping qualities. A fertilizer con- 

 taining a moderate amount of nitrogen and relatively high 

 in phosphoric acid and potash gives a splendid yield. Fer- 

 tilizer is easy to apply and is not likely to cause the devel- 

 opment of scurf. The amount used to the acre varies from 

 600 pounds to a ton. The most economical results are 

 probably obtained by using 1200 pounds to the acre of a 

 3-9-6 fertilizer. Following a clover cover-crop the per- 

 centage of nitrogen in the fertilizer may be somewhat 

 reduced. Lime is of direct benefit to the sweet potato 

 crop, especially where the soil is quite sour. If it is to be 

 used, light applications are recommended. Wood ashes 

 which have never been wet are particularly beneficial for 

 sweet potatoes, because they usually contain 5 to 6 per cent 

 of potash and 30 per cent of quick-acting lime." 



Propagation. 



It is the custom to grow all varieties from shoots or 

 cuttings, although the Spanish variety may be cut .and 

 planted like the Irish potato. The slips are grown in beds 

 and transplanted to the field. Many growers prefer to 

 plant only a small part of the field with the slips and the 

 xeinainder with the prunings from the growth of these 

 slips. Propagation is usually accomplished by means of 

 (1) slips, and (2) cuttings. 



