38 



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



The energy relationships of mech- 

 anized agriculture and the long- 

 term consequences need to be 

 restudied. Nevertheless, it is 

 tempting to believe that long-term 

 energy problems will be solved, al- 

 lowing the continuance and exten- 

 sion of mechanization. 



As previously mentioned, most 

 operations in the production of 

 yams can be mechanized. In order 

 to benefit from mechanization, the 

 scale of farming must be increased. 

 When yams are grown on a large 

 enough scale, two problems not 

 now meriting attention can be 

 studied: the production of seed 

 yams in special nurseries and the 

 mechanization of staking systems. 

 Or, as an alternative, it may be 

 feasible to grow unstaked yams 

 economically when all operations 

 are mechanized. 



In considering the future of the 

 wing-stemmed yam, its competi- 

 tors must be taken into account. 

 The African yams, with their more 

 stringent growth requirements 

 and adaptation to certain climates, 

 will probably not compete success- 

 fully with D. alata except in West 

 Africa and a few other locations. 

 On the other hand, new varieties of 

 D. esculenta recently collected 

 show great promise and may re- 

 place D. alata in some places. 



The real competition for the 

 wing-stemmed yam comes not 

 from other yam species but from 

 other roots and tubers. Chief of 

 these is cassava, Manihot esculenta 

 Cranz, which has already displaced 

 yams in many parts of the Tropics. 



There is no evidence that the 

 march of this crop will be detained, 

 but its victory will be unfortunate, 

 because the food value of cassava 

 does not reach that of the yam. 

 In other areas aroids and sweet- 

 potatoes do and will continue to 

 compete with the yams. To com- 

 pete better, select varieties of the 

 wing-stemmed yam are needed, 

 and based on these varieties, mod- 

 ern agronomical techniques must 

 be developed. 



LITERATURE CITED 



(1) Alexander, J., and Coursey, 

 D. G. 



1969. The origins of yam cultiva- 

 tion. In Veko, P. J., and 

 Dimebedy, G. W., (eds.), 

 The Domestication and Ex- 

 ploitation of Plants and 

 Animals, pp. 405-425. 

 Duckworth, London. 



(2) Berwick, J., Chand, D., and 

 Ralibokala, J. 



1972. Yam (Dioscorea alata) 

 planting rate, staking, va- 

 riety and palatability 

 trials. Fiji Agric. J. 34: 

 44-50. 



(3) BURKILL, I. H. 



1917. A report on races of the 

 greater or ten month yam, 

 Dioscorea alata, cultivated 

 in the botanic gardens, 

 Singapore. Straits Settle- 

 ments Garden's Bull. 9(11- 

 12) : 371-396. 



(4) 



1951. The rise and decline of the 

 greater yam in the service 

 of man. Adv. Sci. 7(28) : 

 443-448. 



(5) 



1951. Dioscoreacea. Flora Males- 

 iana. Ser. I, vol. 43, pp. 

 293-335. 



