CULTIVATION OF THE TRUE YAMS. 7 
Because of the sandy character of most soils where yams have 
been grown in Florida, it has been possible sometimes to raise fairly 
good crops without such preparation of the soil as advised in the 
foregoing, but in these instances the soil conditions have been favor- 
able and commercial fertilizers have been used. Experiments re- 
ported by investigators in the West Indies indicate that it pays well 
there to have the land fully prepared. 
Where it is wholly impracticable to supply the additional humus 
and prepare the land as directed, two applications of a complete 
commercial fertilizer will usually make it possible to raise a yam 
crop. The first application should be given shortly after the plants 
are up and the second may be given six to eight weeks later. A 
good formula for sandy soil is about 6 per cent ammonia, 6 per cent 
phosphoric acid, and 8 to 10 per cent potash. Each application 
of fertilizer may be at the rate of 2 to 2£ ounces per plant. 
HOW TO INFLUENCE THE SIZE OF TUBERS. 
Mention has been made of the large size to which the greater 
}-am may, grow. Some remarkable records have been made in Florida. 
Single tubers of 50 to 60 pounds' weight have been produced at 
the United States Plant Introduction Garden at Miami. From 
Sebring has been received an authentic report with a photograph 
of a 63-pound 3 r am grown in a season of 11 months. There is also 
reliable testimony of the harvesting a few years ago at Crescent 
City of a single yam tuber of three years' growth which weighed 
137 pounds. The quality of all of these large yams was reported 
to be quite equal to that of smaller tubers of the same varieties. 
Very large yams are often misshapen — lobed, branched, or 
" fingered " — and naturally are much less easily harvested, handled, 
and marketed than smaller ones of better shape. Growers of the 
greater yam will usually prefer tubers between 3 and 8 pounds in 
weight. Tubers within these limits when of even form and reason- 
ably smooth surface are especially desirable for market. The size 
of the tubers may be controlled to some extent by modification of 
the planting distance. To keep down the size of individual tubers, 
two or three pieces of tuber may be planted in a hill if there is 
reason to expect only one sprout from each piece. 
According to a report 10 of experiments in Trinidad, an increas- 
ingly large proportion of tubers of regular shape can be raised by 
continuously selecting such shapes for planting. The well-shaped 
tubers were in general much smaller than the others, however, and 
it became necessary after reducing the number of ill-formed ones 
in the crop to begin selection for increased size as well as good form. 
Experiments are under way in Florida to determine what results 
may be secured there by selection. 
SUPPORTS FOR THE VINES. 
Yam vines should be furnished with tall stakes, a trellis, or some 
other support upon which to run, when practicable. (PL Yll, 
Figs. 1 and 2.) In the experience of the department this insures a 
greater yield than can be obtained from unsupported vines. l>e- 
10 Brunton, L. A. Selection iD the shape of vams. In Proc. At:r. Soc. Trinidad and 
Tobago, v. 21, p. 116-1 IS. 1021/ 
