Comparative Analysis Of Costs And Return of Different Yam Species.More over, the study will serve as a future reference to researchers and students even research stations on analyzing and to determine the economic benefits yam production.
1.1 Background of the Study
Agriculture is an important and basic sector for the national economy. Therefore, agriculture remains the mainstay of Nigeria’s economy.
Nigeria is an agrarian country that is endowed with enormous food crop such as yam, cocoa, cassava, rice, sugar cane, maize millet, groundnut and wheat most of which serves as the staple food of Nigerians.
Agriculture is so far, the greatest employer of labour with about 80 percent of the labour force believed to be engaged in farming. It is a major catalyst for economic development of any nation including Nigeria.
Lipton (2005), argued that agricultural growth should reduce poverty through farming.
Agricultural growth results in increased demand for unskilled labour, thus creating jobs and tending to raise the rural wage, general return to land, an asset that some of the poor have when they have few other assets than their labour power; and tends to push down the price of produce, including food, to the immense benefit of the majority of the poor who have to buy in food staples.
Agriculture’s contribution to the Gross Domestic Product (GDP) has remained stable at between 30 and 42 percent, and employs about 65 to 80 percent of the labour force in Nigeria (Aigbokhan, 2001).
It is estimated to be the largest contributor to the non-oil foreign exchange earnings. This means that agriculture holds abundant potential for exchange and sustaining the country’s foreign exchange and provision of food for consumption, fibre and raw material for agro-industries.
In spite of aforementioned benefits, Nigeria’s agricultural output has over the years been on general decline when compared with other sectors of the economy.
Thus, such general decline is attributed to such factors as negligence of the sector labour intensive, technology and as well as inefficient implementation of agricultural policies and programmes on farm production such as yam which in one of the major staple food in the country.
Yam (Dioscorea spp) belongs to the class of crops called tuber crops and they are found majorly in the northern, eastern and western part of the country yam is a major tuber staple in west and central Africa where it provides food for over 180 million people (Idowu, 2005).
Yam, a tropical crop in the genus Dioscorea is an annual root tuber bearing plants with more than 600 species out of which six are economically, socially important staple species in term of foods, cash and medicine (IITA, 2009).
Yam is a staple food crop that is grown in tropical regions and the fifth most harvested crops in Nigeria following after cassava, maize, guinea corn, beans, cowpeas. Moreso, after cassava, yams the most commonly harvested tuber crops in the country (NBS, 2012).
The area harvested in the world has increased from 1.15 million (ha) in 1961 to 5.04 million (ha) in 2012. Yield per hectare in the world also increased from 72.35 thousand metric tons in 1961 to 116.65 thousand metric tons in 2012, (FAO, 2014).
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The total area planted during the 2009/210 season put as 3,236.16 (‘000ha), of this, Benue State led with 396.45 (‘000ha) followed by Niger state with 367.16 (‘000ha) and Taraba State with 272.52 (‘000ha) (NBS, 2007, 2012) while yam production in Ebonyi state has nearly doubled since 1985.
Nigeria is the world’s largest producer of yam with 65 million tones, cote d’ voire and Ghana, only produced 6.9 and 4.8 million tons respectively (FAO, 2014).
Yam is an important agricultural crop in Nigeria and that its importance in the diets of the various tribes in the country differs and it is grown as a source of livelihood its cultivation is very profitable despite high cost of production and price fluctuation in the market and an average profit per seed yam, after harvest and storage, was calculated at over 60%.
Yam (Dioscorea spp) plays significant roles in the social-cultural and economic wellbeing of thousands of people in Nigeria and elsewhere in the world (Babaleye, 2003).
Some of its species are white yam (Dioseora rotundata poir), water yam (Dioscorea alata L), mostly grown in Nigeria (Zanknayiba and Tanko, 2013).
White yam (D. rotundata), is the most widely grown and preferred yam species. The tuber is roughly cylinderical in shape, the skin is smooth and brown and the flesh is usually white and firm.
A large number of white yam cultivars exist with differences in their production and post-harvest characteristics. It has comparative advantages over water yam in terms of marketing value and consumption and therefore gives incentive to farmers to go into yam production because of the value addition and it is regarded as the best yam both for consumption and profit oriented.
This has advised the farmers to pay more attention and effort on white yam production whereas water yam has low marketing value coupled with the reason that water yam is very “watery” in terms of consumption.
Water yam (D. alata), is the most spread specie throughout the world and in Africa is second only to white yam in popularity.
The tuber shape is generally cylindrical, but can be extremely variable depend on the type of land being cultivated. The tuber flesh is white and “watery” in texture. It is a vigorously growing, twining, herbaceous vine reading 10-20m in length, Lebot, et al., (2005).
It is an important food in Africa, the Caribbean, and especially Melanesia when it has considerable social and cultural importance (Lebot, et al., 2005).
A large number of cultivars have been recorded throughout the tropics varying in shape and colour of leaves, stems and tubers.
It give more satisfaction between month of April to August before the availability of new yam because the water content has drastically reduced at minimal level and also has longer shelf-life than white-yam.
The storage temperature for white yam is 16oC at 80%rh and storage life of 4-7 months can be achieved under these condition (Mc Gregor, 1987), whereas for water yam the storage temperature is in the range of 30oC at 60%rh and storage life of 6-9months (Thompson, 1996).
The water content in white yam is 58.80 percent, its carbohydrate is 15-23g, fats and crude protein is 0.1-0.2g and 1.1-2.0g, whereas water yam the water content is 65.78% and its carbohydrate is 22-29%. The fats and crude protein is 0.1-0.3g and 1.1-2.8g, (USDA), 2014.
Despite its importance, yam such as D. alata belongs to the neglected crops and may constraints limit its production. Due to the perishability of the crop, the tubers such as D. rotundata cannot be kept for more than a few weeks after harvesting.
About 50 percent of the crops may be lost within 6 months due to rot or germination if no stabilization processes are used and this explains the volatility in fresh yam prices over the years (Vernier, 1998).
Also, D. alata the high water content and fragility of fresh tubers affects transport and marketing costs. White yam is the most widely distributed species in the humid and semi-humid tropics (Lebot et al., 2005).
1.2 Problem Statement
Symptoms of poverty, hunger and food insecurity are everywhere in Nigeria.
Unemployment and poverty have been identified as the main sources of food insecurity in countries, especially in the rural areas. Yam and its cultivation is becoming more expensive and relatively unaffordable in urban and rural.
Nigeria such as area of the study, as production growth has not kept pace with population growth leading to demand exceeding supply. Yet experts say yam production is decreasing in some traditional producing areas because of decaling soil fertility and increasing pest pressure.
Furthermore, most small-scale farmers in Nigeria are not able to access loans because of lacks of security. One of the major problem facing small-scale farmers in the study area is how to base their farm enterprise on proper cost benefit analysis of white yam and water yam.
Therefore, the situation however, suggest need for proper cost benefit analysis as a basic measure for profitable yam production in yam dependent localities such as Izzi LGA of Ebonyi State.
Moreso, it is doubtful whether the socio-economic characteristics of yam farmers have so far reflected to the rate of input used and output obtained in the production.
They must be guided on what level of input combination that would ensure optimum production.
This situation required conscientious effort to determine types and sources of inputs employed by the farmers as well as white yam and water yam dietary preference.
However, dissemination of information about new technology and innovations in different forms are therefore pertinent to be quickly gained by farmers in order to boost their productivity.
There seem to be adequate information on yam production in the study area.
Although yam production in Nigeria is quite high, there is still a need for increased production of yam to satisfy domestic and foreign demand (Shehu et al., 2010).
Production of yam in Nigeria is believed to be constrained mostly by high cost of production Tanko, et al (2013). Evidently comparative analysis of white yam and water yam is targeted towards achieving efficiency in the production of yam in the study area.
Therefore, this study aimed at providing answers to the following research question.
1.3 Objectives of the Study
The broad objective of the work is to compare costs and return of different yam species in reference to D alata and D rotundata.
Specifically, the objectives include to;
1.4 Test of Hypothesis
Null hypothesis (Ho): There is no significant difference in production of white yam and water yam.
1.5 Justification of the Study
There is a high need for government to improve the access to farmers and storage facilities of yam and other staple food produce in Nigeria such as Izzi LGA Ebonyi State to help them harness the agricultural potential and to meet the over enlarging demand for food yam of the fast growing population the threats that further harm yam production, now technology that target African small holder farmers.
More over, the study will serve as a future reference to researchers and students even research stations on analyzing and to determine the economic benefits yam production.
This will also help them to improve and increase more in producing high quality of yam products and also to estimate the rate at which income could be inverted from yam inputs.
Furthermore, this will also help as a future guide to access the use in the yam input and outputs in Izzi L.G.A and expose constraints of comparative analysis of white yam and water yam in the study area so as to improve the socio-economic status. Therefore, on analyzing of yam will bring about improvement in Izzi and the world in general.
2.0 LITERATURE REVIEW
The need of analyzing the level of yam production in agriculture has been attributed to having a sustainable food production to ensure food security and industrial raw materials for our fast growing population.
These have been the greatest challenges facing growing or developing nations such as Nigeria because of the much dependence on crude.
In this section, the literature was reviewed in line with the following sub-topics; The origin and cultivation of yam, varieties of yam, yam cultivation in Nigeria, importance of yam in Nigeria, factors that influence Yam production in Nigeria, cost and return to yam production in Nigeria, post-harvest losses of yam in Nigeria, methods of yam storage and yam processing in Nigeria, constraints to yam production in Nigeria.
2.1 The Origin and Cultivation of Yam
Yam (Dioscorea spp) is one of the principal tuber crops produced in large quantities in the country. It is a major staple food appreciated for its taste and cultural roles (Bamire and Amujoyegbe, 2005).
It is widely cultivated in the humid rain forest and the guinea savanna.
Yams (Dioscorea spp) is an annual or perennial tuber-bearing and climbing plants with over 600 species out of which six are economically important in terms of food and medicine (IITA, 2009).
Yam belongs to the genus Dioscorea in the family Dioscoreaceae. The family is believed to be among the earliest angiosperms and probably originated in Southeast Asia (Coursey 1976).
The various Dioscorea species apparently followed a divergent evolutionary course in three continents separated by the formation of the Atlantic Ocean and desiccation of the Middle East (Hahn, 1995).
Accordingly, the major food species originated in three isolated centers: Africa, Southeast Asia and South America (Alexander and Coursey 1969).
These centers are also considered areas for independent yam domestication, and represent considerable diversity (Asiedu et al. 1997).
The species D. rotundata and D. cayenensis are native to West Africa (Coursey 1976).
The ‘yam belt’ of West Africa, which comprises Cameroon, Nigeria, Benin, Togo, Ghana and Côte d’Ivoire (Hahn, 1995), is the principal area of yam production.
Within this ’belt’, yam is closely related to socio-cultural life of the inhabitants. For example, for some societies in West Africa, yam is the totem of maleness and also used as a status of wealth based on number, size and diversity of yams offered during feasts, parties and marriage (Hahn et al. 1987).
Raynor et al. (1992), described different yam tributes signifying the various events associated with yam harvesting and consumption in Micronesia.
Yam is among the mandated crops of the International Institute of Tropical Agriculture (IITA), which has devoted considerable resources in collecting yam germplasm for purposes of maintenance, crop improvement and distribution on request (Ngo, 1991).
Of about 11,500 accessions of yam collected worldwide, IITA maintains close to 3000 accessions mainly from West Africa (FAO 1996).
Yam germplasm from other parts of Africa is hardly represented in the collection.
This is the main reason why the status and diversity of yams in other African countries outside the ‘yam belt’ is not known, leading to the perception that yam is only a West African Crop.
2.2 Varieties of Yam cultivated in the world
There are about 600 known species of yams widespread throughout the humid tropics but the edible yams are derived mainly from the most economically important species, which is; White yam (Dioscorea rotundata) originated in Africa and is the most widely grown and preferred yam species.
The tuber is roughly cylindrical in shape, the skin is smooth and brown and the flesh usually white and firm. A large number of white yam cultivars exist with differences in their production and post-harvest characteristics.
The economically most important yam species include D. alata, D. rotundata and D. cayenensis. D. alata originated in Southeast Asia, more specifically in tropical Myanmar and Thailand (Orkwor 1998), and is currently the most diversified and extensively distributed species.
The spread of Asiatic yams, mainly that of D. alata and D. esculenta, took place more than 2000 years ago, reaching Africa around 1000 AD (Coursey 1976).
D. alata was, then, introduced into tropical America from West Africa around the 16th century by Portuguese and Spanish travelers (Onwueme and Charles 1994).
The species D. rotundata and D. cayenensis are native of West Africa (Coursey 1976).
Of the two, D. rotundata is currently the leading species in terms of total area of production worldwide. It is extensively cultivated in West Africa, the West Indies and, to some extent, in East Africa.
The introduction of the African species into tropical America is believed to have taken place as early as the 16th century (Coursey 1967).
Lamarck gave the first description of D. cayenensis in 1792 based on a specimen from French Guiana (and hence the name Cayenne), whereas D. rotundata was described in 1813 by Poiret based on a sample from Puerto Rico long before their African origin was established (Hamon et al. 2001).
These species, however, had limited eastward movement reaching only as far as East Africa. There is little or no cultivation of the African species in Asia (Onwueme and Charles 1994).
Nigeria produces about 31.5 million metric tons of yams annually (CBN, 2003) and is known to be the largest producer of yam in the world.
Yam production in Nigeria has more than tripled over the past 45years from 6.7 million tons in 1961 to 393 million tons in 2006 (FAO, 2007).NBS (2007, 2012) reports show that 27 States in Nigeria produce yam, with total area planted during the 2009/2010 season put at 3,236.16 (‘000 ha). Of this, Benue State led with 396.45 (‘000 ha) followed by Niger State with 367.16 (‘000 ha) and Taraba State with 272.52 (‘000 ha).
The estimated corresponding total outputs were 37,328.17(‘000 metric tons) for the country and 3,914.17; 3,166.12 and 2,854.95 (‘000 metric tons) for Benue, Niger and Taraba States, respectively.
The farm hectarage of yam production has been increasing over the years with corresponding increases in usage of inputs such as fertilizers, herbicides, yam seeds and other agro-chemical inputs.
Unfortunately, the increases in outputs seem not to have been commensurate with those in input usage.
It would seem that whereas the inputs were used at an increasing rate, the resultant outputs were increasing at decreasing rate.
Yam is an important food crop whose production has to be emphasized and being an important food for millions of people in Africa (Babalaye, 2005).
Also yam production in Nigeria has not been accorded the needed attention despite the importance of yam (Orkwor and Asiedu 1999).
This is reflected in the fall in output percentage growth rate of yam from 42% in 1990 to 16.3% in 2001 despite the increase in land devoted for the production of the crop from 1270 million hectares to 2742 million hectares in the same period (Federal Ministry of Agriculture, FMA 2001).
Since increased productivity is directly related to production efficiency, it is imperative to raise productivity of the farmers by helping them reduce technical inefficiencies.
World production of yam was estimated at 58.7 million tons with West Africa producing more than 92 percent (FAOSTAT, 2014).
Nigeria and Ghana together produce about 66percent of the world’s yam supply. As food, yam plays an important role by providing cash and dietary carbohydrate to millions of people.
It has a better keeping quality than most other tropical root and tuber crops because of the tubers have an extended period of dormancy during which physiological activity is at a minimum.
Yam can therefore serve as an important food security crop. The major yam producing areas in Nigeria include, the middle belt (Benue, Nasarawa, Kwara, Kogi and Niger), eastern parts of Nigeria (Ebonyi, Imo, Anambra) and southwestern parts (Philip et al., 2006).
It is a very important food crop in African countries; the region alone represents about 90% of the total world production of edible roots and tubers (FAO, 2007).
Despite the importance of yam, its production in Nigeria has not been accorded required attention (Okwor and Asiedu, 1999).
This reflected on the fall of input making yam to be more expensive and relatively unaffordable in urban areas as production has not kept pace with the population growth leading to demand exceeding supply (Kushawa and polycap, 2001).
Decline in average yield per hectare has been more elastic; it dropped from 14.9 percent in 1986-1990 to 2.5 percent in 1996-1999 (CBN, 2000).
The observed productivity decline in Nigeria from 2001-2006 represents a major challenge to increasing yam production and it’s availability as food in the country.
Agricultural seeds are a strategic input, and yam production cannot expand without propagation technologies to address issues of rapid multiplication of seed yam, quality, and price.
The benefit of technologies that address these issues will be evident in increased productivity, which will translate to improved income for producers and utilization opportunities for the crop.
A systematic and continuousPractice of using only clean seeds will reduce the level of pests and diseases that attack the crop in the field as well as improving the storage life of tubers.
In West Africa, farmer-saved seeds are the predominant source of planting material (Nweke et al. 2011).
There are three major ways by which yam farmers obtain their seeds. First, the same plant is harvested twice in double harvesting or milking.
The first harvest is done between the fifth and seventh month of growing, when the tuber which is mostly used for food is carefully cut off below the coronal roots to avoid damage to the root system.
The roots are then covered with soil and a second harvest of the same plant is done at the end of the season for use as seed yam.
The second method involves the use of small whole tubers (sorting method). Some varieties have the capacity to produce both seed sized and ware sized tubers from a single stand.
At harvest, the small sized tubers are sorted and retained for planting while the larger tubers will be used for food. With this method there is usually a high risk of selecting seed sized tubers that are small due to disease, especially viruses, since the symptoms are typically not visible on the tubers (Nweke, 2014).
A third method of getting planting material is to cut large ware tubers of up to 2kg into seed sized sets of 300-500g. This is referred to as ‘junking’.
This method reduces substantially the quantity of tubers that could be used for food because when seed sized tubers are in short supply, larger tubers are converted to seed yam by being cut into setts.
Usually such setts do not sprout evenly when planted. Some varieties such as ‘Macakusa’, which is in high demand in the major yam producing region of the middle belt of Nigeria, do not produce many seed yam tubers so larger tubers are cut to get enough seeds.
A less widely used method involves cutting ware sized tubers during the first harvest of milking, and burying them in the soil at the base of the plant.
These sets are dug up during the second harvest and planted immediately in a newly prepared field for the next crop (Aighewi 1998).
This production method is practiced by some farmers in the yam growing regions of Nigeria and Ghana. Faced with serious seed yam shortages, some farmers in Southern Kaduna, Nigeria, plant the same sett twice.
After a planted seed yam has formed roots, vines, and leaves, the same seed yam is carefully detached and replanted in a new mound.
Researchers in Nigeria of the National Root Crops Research Institute (NRCRI), Umudike, and IITA, Ibadan, developed the minisett technique to overcome the critical problem of the unavailability of good quality seed yam by improving the rate of multiplication of white yam (IITA1985).
With the technique, the multiplication ratio can increase from the traditional 1:5 to 1:30 (Orkwor et al.
The minisett technique involves the cutting of ‘mother’ seed tubers into small setts (minisetts) of 25-100g which must possess a reasonable amount of peel (periderm)from which sprouting can occur.
The minisetts are treated with chemicals to prevent damage from diseases and pests, planted, and managed to produce small whole seed tubers; these in turn are planted to produce ware
tubers for food.
There is a positive correlation between the size of the minisett and the size of the seed yam produced. This means that minisetts should be cut for a targeted seed tuber size. There are varietal differences in the performance of minisetts; therefore the same size of different varieties may perform differently (Aighewi 1998).
However, the quantity required to plant fields in Nigeria and Ghana, the largest producers in West Africa, is estimated at 7 to 10 million tons (FAOSTAT, 2014).
For many farmers in Nigeria, seed yam are inherited from parents, bought, or acquired as gifts.
The yam seeds are multiplied over and over until productivity becomes very low from continuous exposure to pests and diseases.
Yam has a low rate of multiplication so increasing the area under production could be a major challenge. For farmers venturing into production for the first time, the availability of seed yam is critical because of the high cost.
Hence, the problem of the limited supply of affordable good quality planting material continues to be cited in literature as responsible for low productivity (Ironkwe et al. 2007; Udoh et al. 2008; Ogbona et al. 2011; Asumugha and Ogbona 2013).
2.4 Importance of Yam
The crop is of great nutritional and economic importance to mankind. The tuber can be eaten boiled, roasted, fried, mashed or pounded (Osunde 2008).
It is also acknowledged to provide some 200 calories of energy per capita daily in Nigerian and West African diet. According to Eka (1985), dioscorine which is the major alkaloid in yam is medicinally a heart stimulant.
Moreover, yam is also a source of industrial starch, the quality of which varies with the species, with some of them producing starch with comparable quality to cereal starch (Osisiogu and Uzo 1973).
Yam is a staple food for millions of people in many regions of the tropics including Africa, Asia, the Pacific and Tropical America.
It is the fourth most important tuber crop in the world next to potato, cassava and sweet potato (Levand and Shriver 1998, quoted by Mignouna and Dansi 2003).
Mean annual production for the period from 1990 to 2005 was estimated at 34 million metric tons, Africa accounting for about 95% of the total output (FAO, 2005).
Yam tubers are important in different domains. Nutritionally, yams are a major source of nourishment to many populations in the world (Craufurd et al., 2006).
Pharmaceutically, some species of Dioscorea, particularly Dioscorea zingiberensis, produces high concentration of diosgenin, a chemical used for the commercial synthesis of sex hormones and corticosteroids (Chen et al., 2003; Yuan et al., 2005; Islam et al., 2008).
Agriculturally, yams tubers are used as planting material (Odjugo, 2008; Zannou, 2009). Yam also plays vital roles in traditional culture, rituals and religion as well as local commerce of African people (Izekor and Olumese, 2010).
Also according to Babaleye (2003), yam contributes more than 200 dietary calories per capital daily for more than 150 million people in West Africa while serving as an important source of income to the people.
Yam (Dioscorea spp) is a root tuber crop and arguably the most important crop in Nigeria known as the king of crops for it is not just grown for its nutritional value and as an important source of income but also for its cultural, social, economic and religious significance in many areas of Igbo life (Durno and Stuart, 2005).
2.5 Post-harvest Losses
Post-harvest storage losses have been of concern even to the United Nations which brought it to international focus when it declared in 1975 that “further reduction of post-harvest food losses in developing countries should be undertaken as a matter of priority” (FAO and UNEP 1981).
This led many national governments to take more seriously the problems of storage of agricultural produce.
Although attempts have been made to increase agricultural production by bringing more land into cultivation and use of improved seeds and chemicals, these have been less effective because any apparent gain in production has been lost from the moment the food crop is harvested to the time it reaches the consumers’ table (Oracca-Tetteh 1978).
Post-harvest food losses are one of the important sources of food insecurity in Africa. According to AMCOST (2006), pre- and post-harvest food crop loss among African countries is estimated at about 10%, which is higher than the global average.
Although it has been difficult to quantify post-harvest storage losses, some claim that as much as 20% of yam tubers may be lost to pest attack in storage (Sauphanor and Ratnadass 1985 cited by FAO 1998).
Tropical root and tuber crops such as cassava, yam, and cocoyam are important household food security and income generating crops in many African countries (AMCOST 2006; FAO 1998), and over 5 million people are said to depend on these crops for food, feeds and income.
Thus, losses associated with these crops limit the potential income of the farmers, threatens food security and exacerbates conditions of poverty among rural households, whose income stream depends on the ability to store excess farm produce for a later date (Ntiokwana 1999 cited by Thamaga Chitja et al. 2004).
Although farmers have been known to practice indigenous storage of farm produce, these have been known to be less effective compared to modern storage methods. According to Mughogho (1989), Omoruyi and Orhue (1991) and Tyler (1982), produce stored under the traditional system usually do not keep long and farmers usually suffer great losses.
Thus, there is need for the extension service to actively pursue and communicate knowledge of improved storage methods to farmers since effective storage plays an important role in stabilizing food supply at the household level by smoothing the seasonal food production.
2.6 Methods of Yam Storage and Yam Processing
Farmers have been known to practice indigenous storage of farm produce, these have been known to be less effective compared to modern storage methods.
According to Mughogho (1989), Omoruyi and Orhue (1991) and Tyler (1982), produce stored under the traditional system usually do not keep long and farmers usually suffer great losses.
Thus, there is need for the extension service to actively pursue and communicate knowledge of improved storage methods to farmers since effective storage plays an important role in stabilizing food supply at the household level by smoothing the seasonal food production.
For storage to be effective, crop losses must be minimized (Takavarasha and Rukovo, 1989). Improved methods of storage have therefore been developed which attempt to minimize crop losses and reduce the causes of post-harvest deterioration of yam tubers (Ezike 1995; Fiagan 1995).
The agricultural extension service in Nigeria and in Edo State particularly has disseminated and encouraged farmers’ adoption of improved yam storage methods (Osagie, 1992).
It was hoped that farmers’ adoption of these technologies would lead to food losses, improved income and enhanced food security (Florkowski and Xi-Ling 1990).
However, the widespread and continued use of traditional storage practices by small scale and subsistence farmers in Nigeria despite considerable losses usually associated with these methods (Mughogho 1989) and the availability of improved storage methods (Osagie1992) warrant investigation.
There are three common methods of storing the yam tubers after harvesting. These are storing tubers in barns, on platforms and underground. The barn is the commonest form of yam storage in West Africa.
It is erected in an open place and consists essentially of a series of vertically-oriented poles to which the yams are tied with rope.
The use of open-sided shelves made from live poles, bamboo poles or sawn wood has been recommended to enable careful handling and easy inspection in comparison with Tying tubers to poles which can cause physical damage and rotting (Bencini, 1991).
Source: Internet material
In platform storage, the yams are laid horizontally on an elevated platform; while in underground storage the tubers are placed together in a large ditch and then covered with soil or dry vegetation.
Whichever method of yam storage is adopted, it is essential that the tubers should be well aerated and well shaded. In addition, the stored tubers should be inspected frequently so that rotting ones can be removed, and the sprouts can be removed from those that begin to sprout (Onwueme, 1997).
The use of cold storage for yam tubers would be advantageous in reducing storage losses due to rotting, sprouting and respiration.
However the practice is at present limited by the high cost of continuous refrigeration and by the fact that yams stored at temperatures below 10°C tend to become brown and unsuitable for consumption of Yams (Onwueme, 1997).
Traditionally, processed yam products are made in most yam-growing areas, usually as a way of utilizing tubers that are not fit for storage.
Since pounded yam has so much prestige and is the most popular way of eating yam, two attempts have been made to commercialize the process.
The first was the production of dehydrated pounded yam by drum drying. This product could then be constituted without further processing.
This production was first attempted in Côte d’Ivoire in the mid1960s, under the trade name “Foutoupret”, by air-drying precooked, grated or mashed yam. Attempts to produce fried yam chips, similar to French fried potatoes have been reported from Puerto Rico (Scott et al, 2000).
Recent attempts at more sophisticated processing of yam for export or the production of starch or alcohol have not been commercial successes, largely owing to the high cost of the raw material.
Industrial processing and utilizations of yam include starch, poultry and livestock feed, and production of yam flour. Yams have not been processed to any significant extent commercially.
Dehydrated yam flours and yam flakes have been produced by sun drying. The production of fried products from D. alata has also been attempted recently. Both chips and French fries similar to that of Potatoes have been produced. Preservation of yam in brine has been attempted, but with little success.
2.7 Constraints to Yam Production
In the humid tropical countries of West Africa yams are one of the most highly regarded food products and are closely integrated into the social, cultural, economic and religious aspects of life.
The ritual, ceremony and superstition often surrounding yam cultivation and utilization in West Africa is a strong indication of the antiquity of use of this crop.
Yam as a staple and traditional food is not always available at affordable prices to the poor, and farmers complain of low and unattractive prices which does not cover their cost of production (Durno and Stuart, 2005).
Nigeria, the world’s largest yam producer, considers yam to be a “man’s property” and traditional ceremonies still accompany yam production indicating the high status given to the plant (Nweke, 2014).
The overall significance of yam is gradually declining due to increased competition with other food sources such as cassava and wheat bread.
The multiple weeding required to get good yield is a major cost and limitation to yam cultivation, especially for medium-scale smallholders who do not have sufficient family labour.
Current estimates indicate that quantitative losses are high and this translates into substantial amounts when the labour involved in bush clearing, planting, weeding and harvesting are included (Babalaye, 2005).
From comparison of 235 varieties collected world-wide in the 1970s, it was concluded that the centre of variation of D. alata is first Papua New particular. Selection could overcome the difficulty of producing new varieties in a crop where flowering is sporadic and hand pollination complex.
Lucrative urban markets require the smaller, round or oval varieties with white tuber flesh, free of oxidation (Brown, 1995).
Few studies have been conducted on the physicochemical variation of D. alata tubers. Martin (1974), observed in Puerto Rico that high dry weights are associated with fine structure, dense feel, high quality, and concluded that high density is a varietal character that is not changed much by environmental influences.
In the Pacific, although some preliminary work has been done at the inter-specific level (Bradbury and Holloway 1988), the lack of information on the variation within D. alata hinders its prospective utilization as a high quality exportable vegetable. Egesi et al. (2003) studied the extent of genetic diversity existing for organoleptic properties in 40 water yam varieties cultivated in Nigeria.
Two thirds of their accessions were identified as being suitable for boiled yam, while more than half of these accessions were good for pounded yam. Their results were, however, based on the respective quality attributes evaluated but the physicochemical characteristics of the tubers were not quantified,
Furthermore, D. alata is thought to have been introduced clonally in Africa and its genetic base is narrow as demonstrated by the limited isozyme variation detected between African cultivars (Lebot et al., 1998).
In Vanuatu, indigenous knowledge claims that there is tremendous variation between the culinary and palatability properties of D. alata varieties, some being suitable for certain types of preparation, while others are not, and some being cooked much faster than others.
When the tuber of some varieties is cut open, the colour of the surface begins to change rapidly with the oxidation of polyphenolic compounds and become yellowish or brown. Polyphenolic oxidation is also associated with off-flavours, bitterness and deserves in some cases, special preparations. In most islands of Vanuatu, only certain varieties are suitable for the preparation of the national dish, laplap, a pudding made from freshly and finely grounded tubers steam cooked in Heliconiaindica leaves. Others have to be boiled or roasted in order to be palatable (Bourrieau, 2000).
More than 1000 varieties are currently grown in Melanesia although there are signs of genetic erosion in farmers’ fields (Jackson, 1994).
Traditionally, farmers maintain a wide range of diversity, including varieties with tubers irregular in shape and therefore hard to peel and others with smooth skin and regular shape which are more convenient to use. Harvesting alone can account for 20% of the total production costs and is also largely dependent on tuber shape (Onwueme and Charles 1994).
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