208 Effective Farming 



118. Soils. A sandy or a sandy loam soil that is warm and 

 well drained is best for sweet potatoes. On wet land the roots 

 are likely to be coarse and of poor quality. Although often 

 grown on heavy soils, the crop is likely to be late and not of 

 good quality. Also, particles of the soil usually adhere to the 

 potatoes, which detracts from their appearance. If clay soils 

 are used, they should be well supplied with humus, as this 

 tends to lighten them. Humus is an important factor on light 

 soils, also, and should always be plentifully supplied. 



119. Fertilizing the land. Commercial fertilizer is profitably 

 used for sweet potatoes. On sandy soils potassium is of chief 

 importance and phosphorus next. A large proportion of 

 nitrogen is not needed, as it stimulates too much vegetative 

 growth. The general formula used contains about 1 or 2 

 per cent of nitrogen, 6 to 8 per cent of phosphoric acid, and 

 8 to 10 per cent of potash, but these percentages are often 

 varied considerably, depending on the soil and the price of 

 fertilizer materials. 



Green-manuring is a common practice on sweet potato land, 

 especially in the South. A crop of crimson clover turned 

 under a few weeks before setting the plants supplies both nitro- 

 gen and humus. In New Jersey barnyard manure is often 

 used, but in the South manure is not usually available. 



120. Cultural methods. The crop should be grown in a 

 rotation that does not bring it on the piece of ground oftener 

 than once in three or four years. This aids in combating a 

 very troublesome disease called black-rot. The crop should 

 follow a cultivated one like cotton or corn, in which has been 

 sown a catch crop of legumes, as the cultivated crop will tend 

 to free the land of weeds. 



The depth of plowing is influenced somewhat by the kind of 

 root demanded on the market. A short, well-rounded potato 

 sells best and to secure this sort, rather shallow plowing is 

 necessary. On light soils a depth of about five inches seems 

 to give the desired result, while on heavier soils a greater depth 



