4 BULLETIN 50, HAWAII EXPERIMENT STATION. 
of four varieties of sweet potatoes contained from four to seven 
times as much salt as did those grown at the central station. 
SOIL MOISTURE. 
In Hawaii, where there is an uneven distribution of rainfall as 
well as great diversity of soil types, the moisture content of the 
different soils varies considerably. Some of the soils are so porous 
that the water filters through the surface instead of being absorbed, 
and washes away much vegetable matter. Such soils may be im- 
proved in water-holding capacity by green manuring. Other soils 
are too retentive of moisture and for this reason are detrimental to 
the crop. The sweet-potato crop should not be planted until it is 
known what the soil and rainfall conditions are. 3 
Virgin lands, or fields that have lain fallow for some time, should 
be plowed and all volunteer growth turned under to insure excellent 
soil conditions for the development of the roots of the new crop. If 
the soil contains a suitable amount of moisture the roots will develop 
near the surface, but if it is dry they will grow downward before 
enlarging. Roots growing in a dry soil are difficult to harvest. 
In localities where the fields are flooded after a heavy rain and the 
water remains standing in the furrows for several days, not only are 
the fertilizers leached out of the ridges, but the growth of vines is 
stimulated at the expense of the roots. All the furrows should 
therefore lead into a channel at the lowest part of the field. After 
the standing water has been removed from the furrows, the ridges 
should be examined. On those which are saturated with water the 
vines should be thrown to one side, so that the wind and sun will 
hasten evaporation. After about four days, when these ridges have 
returned to normal conditions, the vines should be thrown to the 
opposite side, so that the newly exposed part will dry out. (PL 
II, fig. 1.) 
METHODS OF CULTURE. 
PROPAGATING MATERIAL. 
Sweet potatoes are propagated either from vine cuttings or from 
slips resulting from the sprouting of shoots from the root. In 
Hawaii terminal cuttings are used almost exclusively, because they 
have the ability to make quick growth and the advantage of being 
practically free from insect pests. Old stem cuttings are likely to 
carry the eggs or larvae of the stem borer and are often the means of 
infesting new fields with the pest. So far as resulting yield is con- 
cerned, no appreciable difference has been found between the ter- 
minal and old stem cuttings. 
In Hawaii, where propagating material can be readily taken from 
the vine at any time of the year, the roots of the sweet potato are 
not usually bedded in the greenhouse in spring for slips. It is only 
when a variety shows signs of degeneracy, in the form of unproduc- 
tiveness, that the sweet-potato roots are sprouted. The terminal 
cuttings are removed in lengths of from 12 to 16 inches, and the large 
leaves and their petioles are stripped from them. The cuttings 
should be moistened and protected from drying when they are not 
to be planted immediately after their removal from the vine. Fresh- 
* Planters may obtain a report on their soils by consulting the experiment station. 
