336 CHAPTER XX 



Natal. It is adapted to fairly warm temperature and a medium 

 rainfall, or, in the absence of the latter, a moderate number of 

 irrigations. 



Although the crop is grown on a wide range of soils, it 

 seems to thrive best on sandy loams with a clayey well-drained 

 sub-soil. It has the reputation of growing on very poor sandy 

 soils, especially along the coast, but for profitable returns it is 

 best grown on soils of fairly high productiveness. Excessive 

 applications of stable or kraal manure tend to produce too much 

 top growth and too little root formation. 



Cultural Methods. — Sweet potatoes are generally grown 

 from slips, from the roots, or more commonly from vines. The 

 latter is the method practised to the largest extent in South 

 Africa. The best practice, though, is to sprout the roots in 

 warm sand and then to remove the sprouts for setting in the 

 field (as they become large enough). As the roots continue to 

 sprout for some time, a comparatively small number of roots 

 will supply sufficient plants for a fairly large sized area. Where 

 the crop is propagated by means of vines, these are cut about 

 1 foot long. 



The crop is ordinarily planted by hand on flat or unridged 

 land in rows two to three and a half feet apart with plants 

 spaced fifteen to eighteen inches in the row. Where the land 

 is not well-drained it is advisable to plant the crop on ridges, 

 as described for potatoes. In the case of vines three-fourths 

 of the cuttings should be buried below the ground and care 

 should bo taken to plant them in soil which is fairly moist 

 or otherwise irrigation must be resorted to. 



The land intended for this crop should be ploughed some 

 time in advance of planting so as to give it time to settle. 

 It should subsequently receive a cultivation or disc-harrowing, 

 to put it into good tilth before the plants are set out. 



Analyses have shown that sweet potatoes take large pro- 

 portions of potash from the soil, as well as fair quantities of the 

 other elements of plant food, and on that account the crop 

 should not be grown continuously on the same lands for any 

 length of time. Eotative cropping is as necessary with this 

 crop as it is with ordinary potatoes, and when the soil shows 

 signs of exhaustion the necessary elements of plant food 

 required should be supplied in the form of artificial fertilisers : 

 " A fertiliser containing 2 to 4 per cent, of nitrogen, 8 per 

 cent, of phosphoric acid, and 8 to 10 per cent, of potash has 



