96 The Sweet Potato . 



other while plowing, then turned back after the plowing 

 is finished. It is not thought advisable to turn vines 

 after the ground is thoroughly covered. After the 

 vines have become large enough to shade the ground, 

 the shade will kill out grass and weeds and keep the 

 surface cool; it is not necessary to cultivate later than 

 this. 



Irrigation. 



In some arid regions where sweet potatoes are grown, 

 it is necessary to supply moisture by means of irri- 

 gation. The most practical method is the open ditch, 

 or furrow irrigation with water, the supply coming 

 from some stream or lake. The greatest quantity of 

 water should be supplied between the time the plants are 

 set in the field and when the vines thoroughly cover the 

 ground. Too much water applied during the latter 

 part of the summer or after the vines have covered the 

 ground may result in an excessive growth and a small 

 yield of stringy potatoes. It is preferable that the 

 water be given at evening or on cloudy days. For 

 some time before harvesting, water should be withheld 

 altogether in order that the roots may properly ripen 

 and mature. 



FEETILIZEES 



Manure is the foundation of successful agriculture.^ 

 Any substance added to the soil to render it more 

 fertile may properly be termed a fertilizer or a manure. 

 The successful producer of sweet potatoes or of any 

 other food plant secures crops that command a selling 

 price in advance or in excess of their production cost 



1 Miller, Farmers' Bull. 999. 



