122 THE HANDBOOK FOR PRACTICAL FARMERS 



to provide the j^lant foods in as nearly the proper 2:)roportion as 

 IDOSsible. 



According to Keitt the sweet potato removes a comparatively 

 small amount of phosphorus, a larger amount of nitrogen, and 

 a very large amount of potash from the soil. The same investi- 

 gator found the following fertilizer mixture satisfactory on 

 South Carolina soils, when applied at the rate of five hundred 

 jiounds per acre : 



200 pounds sulphate of potash. 



100 pounds nitrate of soda. 



400 i:)Ounds sixteen per cent acid phosphate. 



100 pounds nitrate of soda when vines are eighteen inches 

 long. 



Stuckey, who conducted extensive experiments with sweet 

 potatoes , obtained good results on Georgia soils by using the 

 following mixture at the rate of 1,040 pounds per acre : 



1,000 joounds acid phosphate. 

 250 pounds nitrate of soda. 

 675 iDOunds cottonseed meal. 

 300 pounds sulphate of potash. 



Duggar and Williamson show conclusively that in many 

 Alabama soils better results may be obtained by heavier appli- 

 cations of phosphoric acid and nitrogen and lighter applications 

 of potash. 



From experiments conducted at the Illinois Experiment 

 Station, Durst concludes that only manure or steamed bone 

 applied under the ridge is likely to give any material increase in 

 the net value of the crop, after deducting the cost of the 

 fertilizer. 



The following formula is given by Johnson and Rosa, who 

 state that it has been popular among Virginia growlers during 

 the potash famine and has given extremely good results : 



4 per cent ammonia. 



8 per cent acid phosphate. 



The amounts of fertilizers to be used must necessarily vary 

 under different conditions, but it would be safe to use from three 

 hundred to five hundred pounds on all soils which have an 

 abundance of organic matter and increase this to one thousand 

 pounds or more on all thin soils that are lacking in organic 

 matter. Where heavy applications are used, it is best to broad- 

 cast a part of the fertilizer and drill the remainder in the row. 



Experiments, conducted to determine the best form of 

 nitrogen and potash for sweet potatoes, show conflicting results. 



