344 



Journal of the Department of Agriculture. 



hearing in mind always that neither crop requirements alone, nor 

 soil requirements alone, should he taken into account, hut hoth need 

 to be studied together. 



On the sandy loam soils, which constitute more particularly the 

 abode of the sweet potato in this country, and where the climate 

 specially suits its development, it is not essential invariably to supply 

 higli-grade complete fertilizers. Moderate proportions of basic slag 

 on soils which have a tendency to sourness would furnish the cro]) 

 v/ith the necessary phosphate. In the eastern United States it is 

 ci frtomary to apply fertilizers along the lines of the future ridges a 

 week or more before planting by means of a one-horse single-row 

 fertilizer distributor (fig. G). 



The sandy loam soils just mentioned are often deficient in humus, 

 and consequently stable manure, always a suitable fertilizer for sweet 

 potato soils, gives good results if applied, as it is in New Jersey, 

 at the rate of 20 to 30 tons per morgen. Where this i^ not available, 

 the humus-content of the soil is maintained by the ploughing under 

 of cover crops as above indicated. In the Northern States it is the 



Fig. 6. — Single-row Fertilizer Distributor. 



practice to sow crimson clover betw^een the rows at the final cultiva- 

 tion, ploughing it under when preparing the land for the succeeding 

 year's potato crop. In the South peanuts are used tor a similar 

 purpose, and afterwards hogs are sent into the land; they feed on 

 the nuts, but leave the peanut vines and roots in the soil. 



In view of the tendency of green crops when ploughed under to 

 render the soil sour, and all the more when the soil itself has already 

 that tendency, the phosphatic fertilizer to be applied should be basic 

 slag rather than superphosphate, but agricultural lime at the rate of 

 two to four tons per morgen, applied every three years, after plough- 

 ing under the green manure, is suggested, or else half those quantities 

 of burnt lime. 



As already shown, sweet potatoes need potash above all kinds of 

 inorganic fertilizers. In the Northern States for grow'ing a quick 

 maturing crop a fertilizer used to be recommended, containing 2 to 

 4 per cent, of nitrogen, 8 per cent, of phosphoric oxide, and 8 to 10 

 per cent, of potash, but war conditions brought the proportions of 

 potash down to 1 or 2 per cent., or deleted it entirely, the other con- 

 stituents remaining as before. 



