PN-5220 



Figure 6. — Yam mound in Nigeria. 



longer but variable in D. rotundata. Since D. rotundata tuberizes 

 early, a fairly large immature tuber may be present as much as 

 4 months before harvest. These immature tubers, if harvested 

 before dieback of foliage, store longer than mature tubers but 

 tend to sprout earlier in the year than mature tubers harvested 

 later. It does not appear possible to change the annual cycle by 

 planting such prematurely sprouted tubers. 



Abundant and regular rainfall is desirable to produce maxi- 

 mum yields in the African yams. Most cultivars of D. rotundata 

 can tolerate dry spells and can recuperate after a drought to 

 produce almost normally. The foliage of both D. rotundata and 

 D. cayenensis is much less succulent than that of D. alata and 

 much less liable to wilt. Thus, although 7^. alata and D. rotundata 

 are often grown together, the latter is more suitable when rainy 

 seasons are short or unpredictable. 



The early tuberization of D. rotundata makes feasible a type 

 of double harvest not possible in the production of other species. 

 After the tuber has formed, but 1 to 3 months before maturity, 

 the tuber may be removed from the living plant without disturbing 

 its growth excessively. The typical mound (fig. 6) in which 

 African yams are planted facilitates this harvest. Since most of 

 the roots arise from the upper, woodier portion of the tuber, the 

 crown, it is possible to carefully dig around the tuber, cutting 



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