PN-5221 



Figure 7. — Kinds of planting pieces, from left to right, top to bottom: 

 whole small tuber, head pieces, midpieces, tail pieces. 



drained on slopes, the tuber pieces are planted without forking 

 or plowing. Erosion is thus minimized, but weed control becomes 

 critical. Weeds must not be allowed to grow to the point where 

 they can compete with yams for soil nutrients. On the other hand, 

 clean cultivation increases the risk of erosion. A protective mulch 

 is particularly useful in such situations. 



Even in African yams that sometimes produce seed, plantings 

 are always made with seed tubers. The use of tubers makes control 

 of the type of cultivar possible but of course reduces the quantity 

 of tuber available as food. 



Four kinds of planting material can be distinguished (fig. 7). 

 Small, whole tubers produced after the harvest of the principal 

 tuber are ideal seed tubers. Unless they are cut, they tend to 

 germinate uniformly and be free of rot. However, unusually small 

 secondary tubers are often produced by plants infected by virus 

 diseases. The production of good secondary tubers as seed requires 

 a preliminary evaluation of the foliage of the original plant. 



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