10 BULLETIN 16, U. S. DEPARTMENT OF AGRICULTURE. 
a leguminous crop, but since both the vines and the roots are re- 
moved in harvesting (unless used for grazing hogs) they may be 
considered an exhaustive rather than an improving crop. Sweet 
potatoes, however, leave practically everything on the field except 
the potatoes themselves, which are principally starch, and this crop, 
therefore, tends to improve the soil. The vines decay very rapidly 
and their plant-food content, although rather small, soon becomes 
again available. Here again the rotations mentioned are to be con- 
sidered only as suggestive, and any number of variations will readily 
suggest themselves to the thoughtful farmer; but the importance of 
maintaining a bountiful supply of vegetable matter of a kind not 
too rich in nitrogen at the time the field comes in tobacco should 
always be kept clearly in mind when planning the rotation. 
FERTILIZERS FOR FLUE-CURED TOBACCO. 
Bright-tobacco soils as a class are naturally rather infertile; but 
they are light and friable and of a character to respond readily to 
fertilizers, particularly in producing a crop of high money value 
like tobacco. Fertilizers increase the chances of profit from growing 
bright tobacco in two ways. They greatly increase the yield, some- 
times by 100 per cent or more, and if properly balanced they generally 
improve the quality. Because of the natural deficiencies of bright- 
tobacco soils and because of the special adaptability of commercial 
fertilizers te bright tobacco there are no other types of tobacco pro- 
duced in this country on which fertilizers are so freely used, except 
on some of the high-priced cigar-wrapper types in New England 
and Florida. 
A so-called complete fertilizer—that is, one containing each of the 
three materials, ammonia (nitrogen), phosphoric acid, and potash—is 
generally needed, and the maximum yield can not be secured unless 
each is supplied in sufficient quantity. No general rule as to the 
proper proportion or balance between these materials can be given, 
and the farmer must exercise judgment in the matter. The best 
proportion for the three elements is likely to vary considerably 
on different fields, according to the soil and its state of improve- 
ment. As stated, each of these elements has its effect in limiting 
the yield: but, aside from this, there is, broadly speaking, a special 
effect on the quality of the leaf that may be attributed to each 
element. Too much ammonia, especially if-unsupported by a suffi- 
ciency of the other fertilizing compounds, particularly phosphoric 
acid, will make the tobacco coarse, dark, and late in maturing, with 
a tendency to damage by “red fire” or dead spots here and there 
on the leaves. Without a sufficient supply of ammonia, however, the 
tobacco will be small, thin, and poor, although the color may be good. 
