98 The Sweet Potato 



possible enormous yields of a high-class quality product. 



Although fertilizers have become a necessity in the 

 production of the sweet potato when maximum profit is 

 derived, certain kinds of manures may result in actual 

 injury to the quality and so reduce the selling value as 

 to make the crop unprofitable. Some soils may yield 

 profitably to the application of one food element while 

 another may actually retard productive growth. For 

 example, it has been found that liberal application of 

 a fertilizer rich in potash and in phosphorous is es- 

 pecially profitable on a soil filled with undecayed organic 

 matter such as one that has had a green-manure crop 

 turned under, while a heavy application of a nitro- 

 genous fertilizer on such a soil might result in the 

 growth of very luxuriant vines with practically no pro- 

 duction of tubers. It is now believed that applications 

 of potash on certain red clay soils of the South, although 

 causing increased yield, do not produce an increase suf- 

 ficient to warrant its use, notwithstanding that the 

 sweet potato makes heavy demands on the potash-con- 

 tent of the soil. Although the sweet potato responds 

 readily to additions of organic matter to the soil, such 

 as the liberal use of green-manures and barnyard fer- 

 tilizers, these materials cannot be applied directly to 

 the crop without reducing the quality and selling value 

 but can best be supplied to the crop immediately pre- 

 ceding the potatoes. It is now concluded that nitrogen 

 can, other things being equal, be supplied most econ- 

 omically in some organic form, such as cotton-seed 

 meal, rather than nitrate of soda or sulfate of ammonia. 



To understand the proper manuring of a crop of 

 sweet potatoes and the fertilizer requirements of a given 

 rotation, a few fundamental principles involved in 



