THE SWEET POTATO IN HAWAII. 3 
regions where there is no soil, in locations where there is an insuffi- 
cient amount of rainfall, or on high elevations which are exposed to 
the wind. 
The plant thrives from sea level to an elevation of 2,000 feet. 
Growth can be maintained at a still higher altitude, provided the 
location is sheltered from strong winds, which are decidedly harmful 
to the plants. When grown at an altitude higher than 1,500 feet, 
the period of maturity of a given variety varies with the altitude; 
that is, the higher the elevation, the longer will be the period required 
to mature the crop, owing to lower temperatures. 
To make its best development, the crop needs moderate rainfall, 
an abundance of sunshine, and warm nights from the time of plant- 
ing until the vines produce vigorous axillary buds. 
SOIL. 
To produce its maximum yield, the sweet-potato crop should be 
grown in a well-drained, moderately fertile, loose sandy soil. The 
following hints may be of value to planters living in regions where 
there is no soil of this kind. 
Heavy clay soil. — When the sweet potato is grown in heavy clay 
soil, such as local taro soil, it develops a dwarfed and sickly vine 
growth and coarse roots which are likely to be unmarketable, owing 
to their irregular shape. (PI. I.) Clayey soil renders aeration impos- 
sible, since it is extremely sticky during wet periods and closely com- 
pacted during the hot summer months, when it dries out in hard 
lumps. 
To improve the physical condition of such soil, leguminous crops, 
such as cowpeas and velvet beans, should be grown and plowed 
under as green manure. The plowing under of leguminous crops adds 
large quantities of nitrogen to the soil. Preparatory to the planting 
of a second leguminous crop, and before harrowing is done, other 
organic matter, such as rotted stable manure, rice hulls, or chaff, 
should be broadcasted on the plowed field. Rice hulls can be obtained 
from any rice-milling establishment in Hawaii for the asking and 
cartage. The incorporation of organic matter in the clayey soil 
loosens and mellows the soil and enables it to retain sufficient moisture 
for plant growth. 
Soils rich in humus. — The vines make luxuriant growth at the 
expense of the roots when the crop is grown on land containing very 
large quantities of humus. Such land should not be planted to sweet 
potatoes for six months following the successive planting of crops 
having edible foliage, such as green mustard, white mustard, and 
Chinese cabbage. 
Soils in seashore areas. — The sweet potato can be grown very 
successfully on areas not far from the seashore and on soil containing 
a large quantity of sand. Flat cultivation rather than ridge planting 
should be practiced on such land, and organic matter and commercial 
fertilizers should be incorporated with the soil from time to time 
to render it productive. Only those varieties of sweet potatoes 
which have already been acclimated and are adapted to seashore 
conditions should be planted on sandy soil, otherwise the roots will 
contain a high percentage of salt. Experiments conducted at the 
experiment station on land near the seashore showed that the roots 
