tions did not affect yields. Koli pointed out the discrepancies 

 among experimental results of other investigators and concluded 

 that the application of organic material or nitrogen increases 

 yields. These results suggest that fertilizer requirements vary 

 from place to place and require local study for best results. The 

 addition of fertilizer in two or three applications in place of a 

 single application at the time of planting has proved beneficial 

 in Puerto Rico. 



Mineral fertilizer formulas used or recommended in the 

 literature included 1 ton per hectare of 5-10-10 in Puerto Rico, a 

 prohibitive rate in view of the price; 90 kilograms per hectare 

 each of N, P,0,, and KoO in Ghana; and 60, 120, and 60 kilograms 

 of these chemicals per hectare in Brazil. 



Pest Control 



Research in various parts of the world has shown that chemi- 

 cal pesticides effectively control certain pests in yam plantations. 

 Most countries regulate the use of pesticides and establish the 

 amount of pesticide residues permitted on raw agricultural com- 

 modities, including imported commodities. (In the United States, 

 the Environmental Protection Agency is responsible for this 

 activity.) In the following discussion mention of a particular 

 pesticide should not be construed to mean that its use on yams is 

 legal in the United States or in any other country, or that residue 

 tolerances have been established. The reader is cautioned to de- 

 termine the status of every pesticide in the country where it is to 

 be applied and to consult the appropriate authorities of an 

 importing country concerning permissible residues. 



Weeds 



After planting, weeds will normally be a problem. Unless 

 weeds are controlled, vigor of the yam plants will be severely 

 reduced. Therefore, weed control measures should begin as early 

 as possible. 



Weed control should begin even before planting. Care should 

 be taken that mulch or organic material does not introduce weed 

 seeds. In addition, the preparation of land just before planting 

 avoids the establishment of vigorous weeds even before sprouting 

 occurs. Relatively late planting results in earlier and more uniform 

 germination and thus reduces the chance that yams will be 

 dominated by weeds. When materials are available and cheap 

 enough, a mulch applied after planting may be the best weed 

 control. 



As soon as planting is finished and the ground is wet by rains 

 or irrigation, a pregermination herbicide can be applied. The 

 problem is to find a safe, effective herbicide. Frequently, a small 



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