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AGRICULTURE HANDBOOK 495, U.S. DEPT. OF AGRICULTURE 



fertile. Drainage is best when the 

 soil itself is permeable, but ridges 

 and mounds are also useful in pro- 

 tecting plants from flooding. A 

 high level of organic material in 

 the soil is conducive to good drain- 

 age and aeration as well as to good 

 nutrition. 



Land Preparation 

 and Planting 



Because varieties of D. alata are 

 grown in such widespread areas 

 and by peoples with differing cus- 

 toms and skills, many techniques 

 are used in their culture. However, 

 the requirements of the varieties 

 are the same. In this discussion the 

 most advanced techniques are em- 

 phasized, although it is recognized 

 that most yams are now grown, 

 and may continue to be grown, by 

 simpler techniques. 



In Puerto Rico excellent yields 

 of yams can be obtained in deep, 

 well-drained clay soils without 

 plowing or forking. In most soils 

 the practice is to build ridges or 

 mounds of soil by hand or machine. 

 Since yams benefit from the addi- 

 tion of organic material to the soil, 

 such materials can be spread over 

 the soil first and then mixed in 

 and formed into the ridge with a 

 disk plow. This method was de- 

 veloped from primitive hand- 

 mounding, still used throughout 

 most of the Tropics. A second 

 method is to place the organic ma- 

 terial in trenches and to build the 

 ridges over the trenches. 



A particularly effective method 

 for growing large yams is to ac- 



cumulate organic materials in a 

 hole or trench and to plant the 

 seed yam directly in the hole. When 

 very wide spaces are used in con- 

 junction with tall vine supports 

 and large seed pieces, very large, 

 even giant, tubers are produced. 

 Such practices are followed in 

 New Guinea, other islands of the 

 Pacific, and Trinidad to produce 

 large tubers for competition or for 

 ceremonial or display purposes. 



New yams are always planted 

 from existing tubers, pieces of 

 tuber, or aerial tubers. Although 

 most varieties of D. alata can be 

 propagated from a one-node stem 

 cutting (fig. 3), the technique is 

 slow, and the resulting plants need 

 at least a second year to mature. 

 To stimulate root and tuber pro- 

 duction of small cuttings, young 

 stems are cut into pieces with one 

 node and part of the stem on either 

 side. The stem and node are buried 

 in sand or other porous rooting 

 medium and treated intermittent- 

 ly with mist spray for 1 or 2 

 months until rooted. Normally, the 

 first tissue produced at the axil of 

 the leaf is undifferentiated but be- 

 comes the primary nodal complex 

 from which roots, tubers, and 

 shoots arise. 



When aerial tubers are avail- 

 able, they can be used as seed 

 pieces. They usually germinate 

 uniformly and produce vigorous 

 plants. However, aerial tubers are 

 usually small, and many are too 

 small to produce plants of suffi- 

 cient size in one growing season. 

 In replicated trials aerial tubers 



