CULTURAL DIRECTIONS 445 



vine growth at the expense of tuber development. It is 

 also agreed that free applications, unless too liberal, will 

 increase the yield, but the quality will be inferior. Nitro- 

 gen, however, must be used under most conditions, and 

 it is probable that not less than 3 per cent will produce 

 the best results, unless manure has been used or a 

 leguminous cover crop has been plowed down. In the 

 far South probably all of the nitrogen should be derived 

 from organic sources, while in the North a portion should 

 be in soluble mineral forms. 



The mineral elements are much more important than 

 nitrogen. They are essential to large yields of high 

 quality, but potash is more important than phosphoric 

 acid. The growers of the famous sweet potatoes at 

 Vineland, New Jersey, use fertilizers carrying about 3 

 per cent of nitrogen, 7 per cent of phosphoric acid and 

 12 per cent of potash. Voorhees ("Fertilizers." p. 223) 

 recommends, to the acre, 20 pounds of nitrogen, 50 pounds 

 of phosphoric acid and 80 pounds of potash. At the 

 Georgia Station (Ga. Sta. Bui. 25, p. 128) 320 pounds of 

 acid phosphate, 360 pounds of cottonseed meal and 640 

 pounds of kainit an acre have given the best results. 

 Beattie (U. S. D. A., Farmers' Bui. 324, p. 7) recom- 

 mends a mixture composed of 200 pounds of high-grade 

 sulphate of ammonia, 200 of dried blood or 300 of fish 

 scrap, 1,200 of acid phosphate and 400 of muriate of 

 potash. Applications of fertilizer vary from 200 to 1,000 

 or more pounds an acre, depending upon the condition 

 of the land. The best results are obtained from dress- 

 ings made from 10 days to three weeks before planting. 

 When very large amounts of the mineral elements are 

 employed, it is especially important to apply them well 

 in advance of planting, because the tender plants are very 

 susceptible to injury from burning. 



Stable manures are sometimes used in sweet potato 

 culture. They are most valuable on thin lands deficient 



