PROPAGATION OF PLANTS 293 



The depth of plowing will be controlled somewhat by the char- 

 acter of the soil. On very deep, loamy soils it is not always desirable 

 to plow deeply, as it tends to make the sweet potatoes long and 

 spindle-shaped. The market requires a rather short, well rounded 

 potato. On deep soils sometimes the plowing does not exceed four 

 inches in depth, but experience on each type of soil is the best 

 guide in depth of plowing. On soils with compact clay subsoil there 

 is little danger from deep plowing. 



Ridging and Level Culture. Sweet potatoes are most com- 

 monly planted on ridges. These ridges are commonly prepared by 

 first opening up a furrow, in which 200 to 400 pounds of fertilizer 

 per acre are distributed. This furrow is then covered with a back 

 furrow, forming a sharp ridge. Just before planting this ridge is 

 partly levelled with a board scraper or harrow, giving a nice moist 

 soil in which to put the plants. The subsequent cultivation main- 

 tains the ridge. There is no very good evidence that the ridge method 

 is superior over level planting, and many growers fit the land with- 

 out ridging, and give level culture. On wet or cold soils the ridging 

 method probably has some advantage, but in other cases it is largely 

 a matter of convenience and choice on the part of the grower. Prob- 

 ably the greatest advantage claimed for the ridging system is that 

 it facilitates digging. 



Propagation of Plants. Sweet potatoes are propagated in two 

 ways : (1) by plants grown directly from the roots; (2) by slips cut 

 from growing vines. All the early crop is grown from plants, but 

 many growers will produce a part of their late crop from slips. 

 Plants are grown mostly from the smaller sized potatoes sorted from 

 the main crop. Whether using these small potatoes continually will 

 have the effect of reducing the crop in time has never been demon- 

 strated, but since the custom has been long in practice without 

 apparent ill effect, it is believed they are satisfactory seed. It is 

 the custom, however, to throw out all the misshapen roots and use 

 only smooth and shapely potatoes of small size. Most growers prefer 

 " slip seed " rather than that grown from the regular crop, as it is 

 usually free from disease and thought to produce more vigorous 

 plants. For this purpose many growers put out a small area of slips 

 each year for growing the seed stock. 



20 



