away the more or less rootless portion and leaving an intact 

 system of roots. After the hole has been covered, the remnant 

 of the tuber begins to produce a new tuber or tubers. Depending 

 on cultivar, time of removal of the first tuber, and length of the 

 remaining growing season, the newly produced tuber may be only 

 large enough for use as seed or it may be as large or larger than 

 the first tuber. The technique of two harvests is an excellent way 

 to extend the length of the harvest season and indeed may be the 

 chief advantage of D. rotundata. 



The African yams are probably more tolerant of poor soils 

 than are the Asian yams. The soils in Africa where they are 

 produced are chiefly very acid lateritic clays. But among African 

 crops they are one of the most exacting with respect to fertility. 

 Therefore, they are usually planted on newly cleared land. 



Land Preparation and Planting 



Two techniques must be distinguished with respect to land 

 preparation and planting, the African and the Caribbean. In 

 Africa new land is used for yams whenever possible. The smaller 

 trees and shrubs are cut and piled, and the larger trees are 

 ringed. The brush is burned during the dry season. Mounds are 

 then constructed with handtools. The size of the mounds and their 

 form and spacing vary from region to region, but considerable 

 uniformity is generally found in any one region. The mounds are 

 usually the proper size for a single plant but may be large enough 

 to accommodate a dozen or more. 



Within the mound the seed tubers are planted with a small 

 handtool. Custom dictates the depth of planting (5 to 15 centi- 

 meters) and the orientation of the tuber piece. In some places 

 the pieces are not oriented, and in others it is thought necessary 

 to locate the piece with stem end down. A mulch, sometimes of 

 dried grass, is often placed over the mound. This has been found 

 to reduce soil temperature and moisture loss and to lead to better 

 sprouting. 



In contrast to the method of planting yams in West Africa, 

 mechanization of soil preparation has been accomplished in the 

 Caribbean and other parts of the Tropics. The soil is turned deeply 

 by moldboard plow. Large quantities (10 to 25 metric tons per 

 hectare) of organic material are distributed over the soil and 

 sometimes mixed with the soil by rototilling. A disk plow is then 

 used to form the soil in ridges 1 to 1.5 meters apart and 0.3 to 0.5 

 meter high. The seed tubers are normally placed by hand and 

 without orientation about 10 to 16 centimeters below the surface 

 of the soil. This can be done with a planting machine. 



In certain areas of Puerto Rico it is possible to plant yams 

 without excessive soil preparation. When soil is deep and well 



18 



