that includes abundant rainfall and a pronounced dry season. That dry 

 season may be particularly long in the case of D. dumetorum, or short in 

 other cases. The many varieties of D. pentaphylla are adapted to areas 

 with distinct rainfall patterns. The success of yams in a particular region 

 is closely associated with selection of appropriate varieties, particularly 

 when long droughts occur. 



In addition, yams are adapted to different day lengths. Although 

 the evidence is not clear, it seems that day length is the chief factor 

 controlling the annual cycle of sprouting, vegetative growth, flowering, 

 tuber formation, and dormancy of the tuber. With respect to the minor 

 species, little information is available except that varieties that grow 

 well at one latitude do not necessarily do well at another. 



In Guadeloupe, D. pentaphylla seems to be more flexible in sea- 

 son of growth than other species. The cultivar 'WanyaF has been cul- 

 tivated with normal yields from February to October, and also from 

 October to December of the following year. Bulbils are usually produced 

 from July to October, or occasionally as early as May and as late as 

 December. Flowering occurs principally in October and November. 

 Dormancy of the tuber can be short. 



D. transversa can grow beyond its normal season if soil moisture is 

 sufficient, and thus high yields are obtained. If the plants are not staked, 

 dry-matter accumulation peaks at 9 months. If plants are staked, such 

 growth continues until 11 months. Dormancy lasts up to 4 months. 



Land Preparation and Planting 



Because little has been written concerning the culture of the minor 

 yams, only general instructions can be given based on experience with 

 other yam species and on personal observation. 



Although yams are adapted to many soils, important requirements 

 for the minor species as well as the major are that drainage and aeration 

 be provided, and that water supplies be adequate. Loose, deep, fertile 

 soil is best, and poor, exhausted soil is intolerable. Most varieties of yam 

 will not grow well in sandy soils. 



Yams benefit from organic material, compost or manure, incorpo- 

 rated in the ground before planting. They are usually planted in indi- 

 vidual hills or high ridges to provide drainage and increase aeration of 

 the soil. Yams can be harvested much easier from ridges than from flat 

 ground, holes, or trenches. If the soil is particularly heavy, subsoil 

 plowing may be desirable. 



Time of planting is usually adjusted to conform to the beginning of 

 the rainy season. Plant as soon as weather conditions are favorable. The 

 possibility of extending the season of these yams by off-season planting 

 needs study. 



The most common planting materials are pieces of the tuber. Tubers 

 for planting are carefully selected to be free of disease and insect damage 

 and are stored out of the sun and where rains or adverse weather cannot 



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