YAMS

Although it is uncertain from which country yams originated, yams are one of the oldest food plants known. They have been cultivated since 50,000 BC in Africa and Asia. In addition to these continents, yams also currently grow in the tropical and subtropical regions of North and South America.

Yams are one of the most popular and widely consumed foods in the world. They play a staple role in the diets of many different countries, notably those in South America, Africa, the Pacific Islands, and the West Indies. Yams are a good source of potassium and vitamin C.

We have identified two types of yams the White yam Discorea rotundata and Chinese yam that offer high yields under the drought prone, shallow soil, low nutrition conditions found in the Sartenejan Region. Yams are also disease resistant and respond very favourably to light applications of phosphorus based fertiliser.  

 Hairy yam harvest      The hairy yam is tough and high yielding and can be grown on trellises or simply as a ground creeper. The hairy yam is especially good for fries as it naturally forms a crunchy coat on the outside of the fry, and also tastes better than potatoe.
 White yam preparation for planting    

We are researching and fostering the commercial production in the Sartenejan Region of the two most profitable types of yams, the white yam and the Chinese yam.

Left: in 2013 we dug pits and mounded them with 3 yams and stakes. These yams were used to ascertain cooking methods and to provide seed (mini-sets) for 2014.

 White yam plantation  

 

We used the same array in 2014 and added fertiliser to see ig yields could be maintained or improved with reuse of plantings. In 2015 we will grow the yams in rows with only shallow pits but with high mounds as recommended.

     

There are three tested methods tested to improve the yield and profitability of white yams; 1) The use of mini-sets or vine cuttings to improve effective yield, the 2) use of mounds to increase yields, and 3) the use of phosphorus based fertiliser to increase yields.

In the traditional method of growing yam, farmers set aside 25 to 30 percent of the harvested tubers as seeds for the next planting season with the multiplication rate is only about 1:5-10 by weight. In comparison cereals like wheat or rice that have a propagation ratio of about 1:300.

Two methods have been published to increase the multiplication rate of white yams and therfore profitability, vine cuttings and mini-sets.

 White yam cutting    

Vine cuttings

Vine cuttings, with one to two nodes with leaves, are taken from the lateral branches of immature healthy-looking vines before tuber enlargement, and planted into soil with carbonized rice husks.
Once the cuttings formed roots and shoots, they are transplanted to nursery beds where they produce mini tubers, which are then used as the planting material for the next crop. Carbonised rice husks can be cheaply and easily obtained.

A rooted yam vine cutting, which would soon be ready for transplanting in the field. Image by O Adebayo, IITA.

Vine cuttings make more yams are made available to farmers for food or for sale, promotes faster multiplication and better crop quality with nematode infestation free yams.

White yam miniset     

Mini-sets

Mini-sets are yam tubers are cut up into 20-25 g pieces and used to produce planting material for ware tuber production.

 White yam mini-set production  

 

The use of mini-sets enables the production of 10 x 5 kilogram (12 lb) yams from one 300 gram (1/2 lb) yam.

Rapid Multiplication of Yams (Dioscoria species) IRETA Publication No 3/88. Jill E. Wilson and Kim Des Rochers, Carl I. Eevensen, Shirley Tjendana. USP Institute for Research, Extension and Training in Agriculture (IRETA). IRETA Publications USP Alafua Campus Western Samoa. 

To produce yams most farmers in the Pacific plant yam setts that weigh 100 to 600 g or more. This means that they must set aside 10 to 30% of their yam harvest for planting material.

1. Minisetts should be treated and dried as soon as possible after cutting to stop rotting.

2. Dust the cut surfaces with dry, sifted fire ash, or beach sand (well washed or collected from above the high tide mark), or treat with the fungicide and/or insecticide recommended in your country for normal yam planting setts.

3. Air dry the treated minisetts for 2 days, then plant them. Do NOT dry longer.

4. Dry the minisetts in a place that is shady, well-ventilated, and protected from rain and sun. Spread them in a thin layer with cut surfaces facing up. 

5. Sprouting usually ranges from 60 to 80%.

6. The time to sprouting varies with species and cultivar and differences in sprouting time can sometimes be a problem. 

7. It is possible to plant minisetts on shallow infertile soils not good for growing yams for eating and, marketing.

Mounds and fertiliser to increase yield

Kang BT, Wilson JE. 1981. Effect of mound size and fertilizer on white Guinea yam (Dioscorea rotundata) in Southern Nigeria. Summary Plant and Soil. 61(3): 319-327. tested the effect of fertiliser and the provision of mounds on the yield of white yams.

Note: 1,000 kilograms is equivalent to approximately 2,204 lbs; 1 kg = 2.2 lb; 1 HECTARE (Ha) = 2.5 ACRES.

1. Increased mound size increased yield more than fertiliser. had a more pronounced effect on tuber yield than fertilizer.

2. Crops could be maintained for 2-3 years after bush fallow.

3. The yield for the three locations without fertilizers was 7.83 tons/ha on the flat compared with 9.44 tons/ha (3.7 Imperial tons per acre, or 8,300 lbs per acre) on large mound (about 30 cm height).

4. With fertilizer yields were 7.43 tons/ha on the flat and 11.30 tons/ha (4.45 Imperial tons per acre, or 9,960 lbs per acre) on large mound respectively.

Notes: Higher yield with mounds may be due to looser soil for yam growth. Planting on large mounds also resulted in longer tubers and shorter harvesting time.


Fertiliser (15:15:15 NPK) and yam yield

Law-Ogbomo KE, Remison SU. 2008. Growth and yield of white guinea yam (Dioscorea rotundata Poir.) influenced by NPK fertilization on a forest site in Nigeria. Journal of Tropical Agriculture 46 (1-2): 21–24,

Ridges were 1 m apart and 250 g setts were planted at 1 x 1 m spacing to give a density of density of 10,000 plants per hectare.

The treatment with 300 kg 15:15:15 NPK per hectare (660 lbs per hectare) resulted in the maximum yield of 24 metric tons per hectare, or 8.86 Imperial tons per acre, or 20,000 lbs per acre. 

White yam yield with fertiliser