Yam Value Chain

Yam (Dioscorea spp.) Production

Description

Land preparation

Yam (Dioscrora spp) are among the most valued tuber crops in the tropics – West Africa is one among the three largest yam production region in the world and Nigeria is the largest production of yam in the world. Most of the yams grown in Nigeria are from small farm land. Manual preparation involves slashing and burning of debris. Mechanical preparation involves slashing of the land area, ploughing and harrowing. If maximum tillage is practiced, then incorporate organic matter into the soil to ensure adequate drainage, aeration, nutrition and room for tuber growth. The major yam producing areas in Nigeria; in clued the middle belt. (Benne, Kabba, Ilorion, Niger, Nassarawa) Eastern part of Nigeria (Owerri, Onitsha, Port Harcourt, Umuahia) Western pest (Ondo, Oyo, Ibadan) Mid-West (beine and delta areas) yam is well distributed in the humid tropics of West Africa were they are valued as an important source of food.

Climatic and Soil Requirements

Soil type

The best soils for growing yams are the sandy clay loams. However, yams can be cultivated on most soil types once the yam holes are properly dug and filled with organic material. Organic matter improves soil structure, acts as a slow release fertilizer and allows for optimal growth of the tubers. Adequate drainage, proper aeration, a friable soil and sufficient moisture (not waterlogged) are other critical requirements for yam growth.
• pH: 4.5-6.5
• Shade:
Yams are sensitive to shade leading to low yields and should be grown under full sunlight.

Temperature
Yams strive under warm – sunny conditions at temperature of between 25oc – 30oc and does not tolerate freezing environment thus yam is restricted to the tropics. Most yam producing area are in the region were the annual rainfall is 1200mm or more and also evenly distributed in districts were the rainfall is as high 300mm/annum.

Variety

Discorea rotundata (white yam)
Discorea alata (water yam)
Discorea cayenensis (Yellow yam)
Discorea dumentorum (Trifoliate Yam)
Discorea bulbifera (Aerial yam)
Discorea esculenta (Chinese yam

Planting

Planting materials
There are four ways of propagating yams:
• Tubers: This is the most important method of propagation in the field. The planting material is called a “sett” and the size of each sett should be between 400 grams to 500 grams. Pre-germinate setts in moist sawdust or coconut husk.
• Seeds: True seeds found on vines e.g. Cush- cush.
• Cuttings: Basal vine cuttings are best. Use 6 cm-8 cm pieces, dip in a rooting hormone and place in a propagating bin.
• Tissue culture: This is used to produce “clean” plantlets i.e. free from diseases.
Note that, there are three types of setts that can be obtained from a whole tuber:
• Head setts
• Middle setts
• Tail setts
The head portion of yam tuber sprouts more easily than the middle and tail portion, as the head has more buds and is less prone to rot than the middle and tail portion. The head produce higher tuber yield than the middle and tail portion. Therefore, it is better to use the whole tuber rather than sets, due to the following reason:

• Its ability to sprout fast
• Produce tuber with higher average weight than the set
• The whole tuber on like the yam set do not have a cut surface and therefore less prone to rot.
• Whole tuber produce higher tuber harvest multiplication ration than set.
Dept of planting should be 9 – 12cm with the uncut surface down ward germination start 30 – 60days after planting depending on rainfall.

Planting methods
There are four main methods of planting yams:
• Ridges: Form ridges 1m apart and 25-40 cm high. Fill furrows with rotted organic matter then plants the yam setts.
• Heaps or Mounds: Heap soil into a small mound and add organic matter evenly before planting.
• Holes: Dig hole 45cm x 45cm x 45 cm and fill with rotted organic and sharp sand in the following ratio- 1:2. Plant one yam set in hole.
• Flat: Minimum tillage is done and vines are allowed to grow flat on the ground without making ridges or heaps.

Crop management

Mulching: covering of ridges or mounds with dried grasses is essential during dry season to help conserve moisture thereby providing optimum condition for growth.

Staking
This is provision of support structure so as to enable yam vines expose their massive canopy to maximum sunlight throughout its growth.
• Individual staking: One stake per plant e.g. bamboo stakes.
• Pyramidal staking: The support structures are slanted to form a peak.
• Trellising: String wire between two strong posts and each stem is trailed along a string towards the wire support.

Weed control
The yam field should be kept weed free the first four months. Farmers have two options for weed control which is the use of traditional method and the use of herbicides. Three to four hand weeding carried out at 3, 8, 12 and 16 weeks after planting have been found effective for the control of weeds in both ware yams and yam production. The critical period of weed interference for seed yams using the minisett technique is 12- 16 weeks after planting, while that of ware yams is between 4 and 16 weeks after planting. Use a contact herbicide in the furrows during growth and manually remove weeds from around the plant. Selective herbicides can be used to control grass weeds and manual methods can be used to control broad-leaved weeds.

Fertilizing
Soil test should be done to determine fertilizer types and rates and also any limestone requirements.
• Two months after emergence apply 85 gm–114 gm of 16:8:24 NPK fertilizers placed 15 cm – 20 cm away from the base of the plant.
• Six months after planting, a similar amount of potash fertilizer e.g. Muriate of Potash is recommended to encourage optimum tuber bulking.
Best yields are achieved using high levels of organic manures and high levels of potash.

Pest and diseases management

The major disease problem is anthracnose (Colletotrichum gloeosporioides).
Anthracnose is normally seen as small, black spots between the leaf veins. This disease can be significantly managed using a number of cultural practices with a combination of timely chemical control:

• Soak the planting material and wet planting holes with recommended copper fungicides prior to planting and after planting respectively.
• Vines are sprayed upon shoot emergence.
• Alternate fungicides to prevent the build up to chemical resistance.
• Ensure adequate levels of nutrients.
• Sanitize the field by raking and removing fallen leaves prior to cultivation to reduce the source of the inoculum (spores of the fungus).
• Practice crop rotation.
• Inter-crop with maize.
• Use windbreaks on the windward side of the crop.
• Inspect the field continuously and rogue out infected plants, especially at the windward side of the field.

Harvesting and Post-harvest Handling

Natural dieback of Yam vines and yellowing of leaves signifies senescence. Yam matures between 9-10 months after planting. After removing the vines, lift the tubers using hand forks taking care to do as little damage to the tubers. The early crop matures at the end of July, main crop from the month of October to January.

Problem of yam production

Scarcity and bulk of planting material: The planting materials are bulky and scares
It is labour intensive
Short shelf live and only limited to dormancy period of 4 months after harvesting

Storage

Barn storage or under front storage
It can also be stored under-ground.

Yam Processing in Nigeria

Yam is the common name for some species in the genus Dioscorea (family Dioscoreaceae). These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania. There are many cultivars of yam though only six are important as staples in the tropics. The economically important species grown are Dioscorea rotundata (white yam), Dioscorea alata (yellow yam), Dioscorea bulbifera (aerial yam), Dioscorea esculenta (Chinese yam) and Dioscorea dumenterum (trifoliate yam). Yams are high in vitamin C, dietary fiber, vitamin B6, potassium, and manganese; while being low in saturated fat and sodium.

Worldwide yam production in 2007 amounted to 52 million tons, of which Africa produced 96%. Most of the world’s production comes from West Africa representing 94%, with Nigeria alone producing 71%, equalling more than 37 million tons. Though yams can be stored up to six months without refrigeration most of the yearly production is lost through spoilage because of lack of post-harvest facility in the country.

In Nigeria, though yams can be consumed by boiling, roasting and processed to yield Amala (especially in the South western part of the country), it can also be processed into the production of instant yam flour.

The traditional method of making pounded yam which requires physical pounding with mortar and pestle is very laborious and in some cases unhygienic. The increasing number of middle class family and the rise in health consciousness amongst the populace is making the traditional way of processing pounded yam in Nigeria fast becoming a thing of the past as more and more family are shifting from the use of mortar and pestle to ready processed yam to be used for pounded yam production.

The process of producing instant yam flour is quite simple; it involves slicing, parboiling, drying and milling of the product to yield flour. The machinery and equipment required for production can be sourced locally or from abroad, and they include;

• Yam slicer
• Yam parboiler
• Hammer mill with cyclone
• Industrial nylon sealing machine
• Weighing machine.

The production process is highlighted below;

Yam selection; fresh harvested yam gotten from the farm are sorted to select whole-some tubers that are suitable for the production of instant pounded yam flour. Usually the mature white varieties of yam are most suitable.

• Weighing; the selected yam is weighed properly
• Washing; the yam tubers are washed properly in order to get rid of sand and other extraneous materials.
• Peeling and slicing; the washed yam tubers are peeled and then sliced to desired thickness.
• Parboiling; the sliced yam are then put into boiling water over a period of time depending on the thickness of the slices.
• Drying; the parboiled yam slices are dried in a dryer at a specified drying temperature and time.
• Milling; the dried yam slices are milled directly into flour of uniform particle size.
• Packaging; the instant pounded yam flour is the finally packaged in moisture proof nylon bags.

Raw materials, supplies and inputs

The only raw material required for the production of instant pounded yam flour is yam tubers. Nigeria has an abundant supply of yam, especially in the middle belt, south west (Oyo, Ondo and Osun states) and some parts in the North and Eastern Nigeria. The major item of supplies is the packaging materials. Other supplies required include; factory wears (overall, hand gloves, factory shoes, nose masks), disinfectants e.t.c. Electricity, diesel (for generator and project truck) and water are the major utilities required for a smooth production of instant pounded yam flour. http://agriculturenigeria.com/agro-processing/processing-of-crops/yam-processing

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World Production and Trade

Most of the world production of yam is from Africa (about 96%) with Nigeria alone accounting for nearly 75% of the total world production. World annual production was estimated to be 25 million Mt in 1974, and 24 million Mt in 1992. During the past 5 years, total world production has increased from 32.7 million Mt in 1995 to 37.5 million Mt in 2000. Also during this period, export quantity declined slightly while export income remained fairly steady. During the period 1975-90, total yam cultivated area increased by about 38.8% globally, while the total production increased by 45.8%. However, the importance of yam in the economy of the main producing areas appears be declining due partly to competition with other crops like cassava in Nigeria, and taro in the South Pacific (Opara, 1999). The major producing areas have also continued to experience high population growth rates. During the last four decades, the annual growth rate (%) of per capita production in the major yam zones in Africa has declined (Dorosh, 1988).

Primary product

Yams are mainly grown for direct human consumption and are marketed as fresh produce in all the growing regions. Common methods of preparation include boiling, baking or frying. Boiled and baked yam can be eaten with vegetable sauce or palm oil. Boiled yam can also be pounded or mashed in mortar and eaten as „fufu‟ or „utara‟. Commercially food processing equipment for boiling and mashing of yam into fufu at the press of a button are now available in the market. Yam cultivars, which contain toxic substances such as dioscorene, are first sliced and soaked in salt water for several hours before further processing for consumption.

Secondary and derived product

Yam tubers are also processed into several food products such as the yam flour, which are enjoyed in many parts of the tropics. Industrial processing and utilisation of yam includes starch, poultry and livestock feed, and production of yam flour.

Requirements for export and quality assurance

There are no specific standards for yam export, but intending exporters must seek information on the quality and phytosanitary regulations of the importing country as well as the product specifications required by the importer. As a guide, exporters should apply the general requirements for the International OECD Quality Standard (Opara, 2001) which issues such as minimum requirements, quality requirements, sizing, tolerance and packaging. These should be interpreted to assist in meeting the specifications agreed with the importer.

Consumer Preferences

There are considerable consumer preferences for the different yam varieties among the growing regions. White-fleshed yams which have firm texture (mainly D. rotundata) are the most popular in West Africa, while in the South Pacific, D. alata cultivars (water yam, white purplish with loose watery texture) are most common (Opara, 1999). Consumer preferences might account for some of the predominance of certain cultivars in some region, in addition to agro-climatological impacts on the growing attributes of the species. In parts of West Africa, yams, which have loose texture, are often mixed with gari and pounded with gari to prepare fufu of „soft‟ texture.

 Post-Production Operations

Pre-harvest Operations

Maturity assessment is critical to achieving good quality yam. In the field, mature crop is generally distinguishable by cessation of vegetative growth and yellowing of leaves. The period from planting or field emergence to maturity is variable depending on the species, and there is no standard reliable and objective index of yam tuber maturity. Some crude indices have been reported based on percentage of tuber length that was whitish at harvest, non-friable after cooking, or bitter after cooking (Onwueme, 1977). The most frequently reported measure is the period from planting to harvest (growing period), but it has been suggested that the time from emergence to maturity provides a better measure of growing period since planted tuber can remain dormant for some time (Onwueme and Charles, 1994).

Most edible yams reach maturity in 8-11 months after planting. Techniques such as using physiologically aged planting material, pre-sprouting of setts, application of sproutpromoting substances (e.g. ethephon and 2-chloroethanol and harvesting before complete shoot senescence can decrease the during of field dormancy and thereby reduce the length period from emergence to maturity (Onwueme, 1977; Gregory, 1968; Martin et al., 1974). In many parts of West African yam zone, mature yams are harvested at the end of the rainy season or early part of the dry season, which coincides with the end of vegetative growth. Yams for long-term storage (for marketing or seed) are usually harvested during the harmattan period (Dec-Jan) in many parts of southeastern Nigeria when the crops has attained maximum growth and maturity. During this period, the soil is generally hard and tuber breakage during harvesting can be an economical problem.

Transport and Packaging

After harvest, yam tubers are traditionally placed into woven baskets made from parts of the palm tree or coconut fronds. These are ideal for transporting small quantity of tubers over short walking distances. The basket is carried on the head, shoulder, or tied to a bicycle and transported to the market or storage facility. Compression damage is reduced since the basket is able to bend and thereby reduce the amount of force acting on individual tubers. However, when large quantities of tuber are harvested, these baskets are not suitable because of their limited size. Packaging tubers in full telescopic fibreboard cartons with paper wrapping or excelsior reduces bruising and enables large quantity of tuber to be transported over long distances. Tubers can be contained in loose packs, or units of 11 kg and 23 kg (McGregor, 1987). The cartons are hand-loaded or unitised on pallets. Storing yams in modified atmosphere packaging (MAP) has beneficial effects, particularly using appropriate packaging material with suitable size and number) of holes for gas permeation. Sealing yam tubers in polyethylene film bags reduced storage losses due to weight loss and development of necrotic tissue (Table 5). Coating tubers with Epolene E10 (a commercial vegetable wax improved the appearance quality but there was no effect on levels of fungal infection (Thompson et al., 1977). The effect of this treatment on weight loss of tuber was inconsistent.

Curing of Yam Tuber

Curing of root crops allows tuberization of surface injuries and reduces subsequent weight loss and rotting in root crops. Curing of yams is recommended before storage so as to “heal” any physical injury, which may have occurred during harvesting and handling. This can be accomplished under tropical ambient conditions or in a controlled environment. Traditionally, yams are cured by drying the tubers in the sun for a few days. The optimum conditions for curing are 29°-32°C at 90-96% rh for 4-8 days (McGregor, 1987). Tubers cured at higher temperature (40°C) for 24 hours or treated with gamma radiation at 12.5 krads were free of mold and had least losses during subsequent storage. Storing at 15°C with prompt removal of sprouts was found to improve the eating quality of tubers (Coursey, 1967), presumably due the water loss associated with curing and the inhibition of the biochemical synthesis that accompany sprouting.

Cleaning

Prior to long-term storage and marketing, yams are cleaned (without water) by scrapping off soil and other debris on the surface. A knife or piece of stick is usually used. The root „hairs‟ are also removed to so that the tuber has a smooth surface. Water must not be used to clean tubers before storage because of increased susceptibility to microbial infection and growth under the ambient humid storage conditions. http://www.fao.org/3/a-ax449e.pdf

Proper packaging and handling

The ideal in packaging is to protect the produce from damage during handling, transport and storage and to provide containers of uniform size that are conveniently stacked and handled, easily accounted for in quantity and, where appropriate, in weight.

In many developing countries traditional baskets, and various types of trays or buckets are used for transporting produce to the house or to village markets. These are usually of low cost, made from readily available material and serve the purpose for transport over short distances. But, they have many disadvantages in large loads carried over long distances:

• they are difficult to clean when contaminated with decay organisms;
• they often lack rigidity and distort when stacked thus applying severe local pressure to their contents
• they are frequently very variable in shape and therefore are difficult to load, especially for long journeys.
• being of local manufacture they are often rather crude and may have sharp edges or splinters causing cuts and punctures to the commodity.

Many authorities have observed that produce being transported and marketed in commercial quantities needs better packaging in appropriately sized units if losses are to be minimised and to achieve economical use of transport. The shape of packages is significant because of need to load for maximum capacity and stability. Round baskets, whether cylindrical or tapered, hold considerably less produce than boxes occupying the same cubic space; a cylindrical basket contains only 78.5% by volume compared with a rectangular box occupying the same space on a vehicle.

However, packaging can be a major item of expense in produce marketing, especially in developing countries where packaging industries are not well developed. The selection of suitable containers for commercial scale marketing requires very careful consideration. Among the various types of packaging material that are available¹, natural and synthetic fibre sacks and bags as well as moulded plastic boxes seem to be more suitable and have greater promise for packaging roots and tubers and for their transport to distant markets

Including sawn wooden boxes, cardboard boxes, moulded plastic boxes, paper or plastic film sacks, natural or synthetic fibre bags.

Control of Temperature

Temperature has a great influence on many factors that cause loss during storage. It is the single most important factor affecting the rate of respiration, it also influences the rate of sprout growth, the development of rotting micro-organisms and insect infestation. Figure 4.8 illustrates the effect of different temperature regimes on the storage of potatoes. At 10°C, the rates of sprout development, rotting and respiration are shown to be moderate but at 4°C, sprouting is stopped, while rotting and respiration continue but at very low levels.

With the exception of highland areas, low temperature storage in the tropics within the range 10° to 15°C can only be envisaged by using a refrigeration process of some kind. At subsistence or small farmer level this is generally not practical because of cost implications and the technical support needed to sustain conventional refrigeration technology. Only in very dry areas is simple evaporative cooling at all successful but even this simple technology needs a prime mover to be operating almost continuously. Therefore, successful storage of roots and tubers in any sort of structure depends very much on natural ventilation to remove respiration heat, to remove carbon dioxide, which in concentration can lead to the breakdown of dormancy, and to keep the temperature of the crop as low as possible. Ventilation should be with the coolest possible air, night time ventilation is not only the coolest but has the highest relative humidity, so that water loss through transpiration is also held to a minimum. http://www.fao.org/docrep/x5415e/x5415e03.htm#TopOfPage.

Constraints to Yam Production

The problems faced by farmers in yam production in the area include lack of adequate farm inputs (50%), high costs of hired labour (83.3%) and lack of improved seed yam (66.7%). This conforms with the findings of Rueben and Barau (2012) and Sanusi and Salimonu (2006) which listed the same variables as constraints to yam production in Taraba and Oyo States respectively. Others constraints faced by the farmers are lack of extension services (100%), inadequate fund (95%) and the problems of diseases and pests among others.

http://article.sapub.org/10.5923.j.ijaf.20140406.04.html

References

http://agriculturenigeria.com/agro-processing/processing-of-crops/yam-processing

http://21stplacelive.com/Yam%20buyers.htm

Click to access a-ax449e.pdf

http://www.fao.org/docrep/x5415e/x5415e03.htm#TopOfPage.

http://article.sapub.org/10.5923.j.ijaf.20140406.04.html

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