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. Ni- 
trogen, however, must be used under most conditions, 
and it is probable that not less than 3 per cent will pro- 
duce 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. 
One thousand two hundred pounds to the acre ,of a 
3-9-6 fertilizer, and light applications o.f lime, are recom- 
mended in New Jersey (New Jersey Station Circular 
1 14). For Northern commercial sections, where the 
sweet potato is grown as a truck crop, and the brief 
growing season makes quick maturity necessary, a fer- 
tilizer containing 2 to 4 per cent of nitrogen, 8 per cent 
of phosphoric acid, and, when available, 8 to 10 per cent 
of potash, is recommended by Miller in Farmers’ Bulle- 
tin 999. On the sandy loam soils of the South, where the 
sweet potato is a farm crop, and Avhere the climate is 
more favorable, good yields may be secured by applying 
a mixture of 1 part of cottonseed meal to 2 or 3 parts of 
16 per cent acid phosphate at the rate of 500 to 600 
pounds per acre drilled under the row in preparing the 
land for planting (Farmers’ Bulletin 999). 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 dressings 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 
