THE SWEET POTATO IX HAWAII. 
IRRIGATION. 
Irrigation is not an important consideration in connection with 
sweet-potato growing in Hawaii owing to seasonal conditions and 
the drought-resistant character of the plant. It thrives and pro- 
duces a crop of roots with very little moisture. The type of soil and 
the amount of rainfall largely determine where and when the crop 
can be grown to the best advantage. When rainfall is the only 
source of moisture, the crop should be frequently cultivated to con- 
serve moisture as the dry season approaches. 
The plants should be watered sparingly when they are ^rown on 
small areas or in localities where irrigation is possible. It is impos- 
sible to establish a definite rule for time of irrigation, because some 
soils retain moisture longer than do others, but it is good practice to 
water the plants when the soil, to a depth of 3 or more inches, is 
comparatively dry to the touch. 
A very effective way of irrigating the sweet-potato crop is by 
turning the water into alternate furrows. This practice permits 
thorough saturation of the soil immediately surrounding the plant 
and precludes the possibility of its packing later. In flat culture 
light irrigation, rather than heavy, should be practiced. 
PRUNING. 
Some of the local growers cut the sweet-potato tops from the 
cultivated field for feeding hogs. To determine the effect of such a 
practice upon yield of roots the experiment station, in 1917, carried 
on a test, covering eight months, with the Yellow l am variety of 
sweet potato. The plants were set in 12 rows, each 100 feet long, 
and the vines were cut once a week after they had attained a length 
of 18 inches. The following table gives the result of the test: 
Effect on yield of cutting back sweet-potato vines. 
Rows. 
1, 2. 3, 4.... 
5,6, 7,8.... 
9, 10, 11, 12. 
Length to 
vhich vines 
were cut. 
Inches. 
12 
C 1 ) 
18 
Calculated 
acre yield. 
Pounds. 
6, 859. 4 
21, 857. 6 
10, 779. 1 
1 Not pruned. 
The above table shows that the yield of sweet potatoes is greatly 
decreased when the vines are cut back. The rows, the vines of which 
were kept within 12 to 18 inches long, produced a yield of roots 
approximating 31 and 49 per cent, respectively, of a crop as compared 
with the unpruned vines. The test showed that many pruned vines 
were devoid of enlarged marketable roots. Apparently the shorter 
the vine is cut, the greater will be the reduction in yield. 
HARVESTING. 
The period of maturity of the sweet potato differs with the variety 
and the locality in which it is grown. Some varieties mature a crop 
much earlier than do others. In all varieties the period required for 
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