2.1 Description of the study area in the Northern Region
2.2 The cassava plant
2.3 Traditional drying and storage structures of dried cassava chips
The field survey was carried out in the Republic of Ghana, West Africa. Ghana is bounded on the east by the Republic of Togo, by the Ivory Coast on the west, on the north by Burkina Faso and by the Atlantic Ocean to the south (see Figure 1). Five ecological zones can be described in Ghana: the high rainfall forest (4%), semi-deciduous forest (21%), transitional zone, coastal savannah and northern savannah.
Figure 1: Map of Ghana showing national and regional borders
In 1994, Ghana had a population of about 17 million living in an area of 238537 km2. Out of this total land area, 136282 km2 can be classified as agricultural land, but only about 43200 km2 are under cultivation (PPMED, 1994; Statistisches Bundesamt, 1994). Agriculture is vital to the overall economic growth and development of Ghana. It is also the largest contributor to the Gross Domestic Product (GDP), accounting for about 50% (PPMED, 1991). The greatest production emanates from root and tuber crops including cassava, yams and cocoyams, contributing about 46% to the agricultural GDP. Table 1 summarises land area cultivated and production of major crops in Ghana for the 1994/95 season. The data highlight the importance in the agricultural sector of root and tuber crops, which contributed nearly 76% of total major crop production. In terms of quantity produced, cassava is the most important root crop in Ghana followed by yams and cocoyams, but today cassava ranks second to maize in terms of area planted (R. Al-Hassan, 1991).
Table 1: Most important crops grown in Ghana, production estimates and land area cultivated (1994/95)
|
Major Crops |
Area in ha |
Production estimates in metric tons |
|
maize |
668600 |
1034170 |
|
rice |
99900 |
212290 |
|
millet |
193400 |
209000 |
|
sorghum |
334500 |
360100 |
|
cassava |
551250 |
6611440 |
|
cocoyams |
204500 |
1383200 |
|
yams |
176140 |
2125700 |
|
plantain |
212460 |
1637480 |
source: PPMED, MOFA, Ghana, January 1995
Table 2 documents the production increase of cassava over the last three years, which is about 17%, on an area under cultivation more or less stable. It shows that the yield per ha is increasing but it is still low compared to major producing countries such as Brazil. Although the description shows that the overall cassava production trend is positive, farmers efforts to increase production are hampered by a number of constraints in the rural areas. Low prices, uncertain access to markets and low production technologies are still major obstacles for semi-subsistence farmers to increasing the area for cultivation of cassava.
Table 2: Production and area estimates for cassava in Ghana, 1992-1995
|
Year |
Production estimates in Mill. metric tons |
Area in ha |
|
1992 |
5662 |
551930 |
|
1993 |
5997 |
531840 |
|
1994 |
6025 |
520410 |
|
1995 |
6611 |
551250 |
source: PPMED, MOFA, Ghana, January 1995
Cassava is grown throughout Ghana, although production is concentrated in the south (see Figure 2). It is cultivated as a monocrop or intercropped, either as the dominant or subsidiary crop (R. Al-Hassan, 1991).
Figure 2: Intensity of cassava production by regions in Ghana
Table 3 shows the summary of regional cassava production in the country and which areas have relatively more important cassava production. The bulk of the nation's cassava is produced in the south and middle of Ghana, which accounts for roughly 78% of the total cassava production in Ghana. In the Northern Region of Ghana only 2% is devoted to cassava production (see Figure 2). But the production and area under cultivation in Northern Ghana is increasing due to the fact that cassava also grows on marginal land and yields a sufficient amount for the semi-subsistence farmers, who often lack cash for fertiliser or other costly inputs for crop production.
Table 3: Production and area estimates for cassava in each region in Ghana, 1995
|
Regions |
Production in metric tons |
Area in ha |
|
Western |
512400 |
55900 |
|
Central |
608200 |
55500 |
|
Eastern |
1920000 |
160000 |
|
Gt. Accra |
103400 |
24600 |
|
Volta |
917000 |
51900 |
|
Ashanti |
1066940 |
106700 |
|
Brong-Ahafo |
1347000 |
77650 |
|
Northern |
136500 |
19000 |
source: PPMED, MOFA, Ghana, January 1995
Northern Ghana is situated between 8°-11° N latitude and 0°-3° W longitude. Administratively it comprises the Upper West Region, the Upper East Region and the Northern Region (Runge-Metzger and Diehl, 1993). The Northern Region is the largest region of Ghana, comprising 41% of Ghana's land area, but has the lowest population density of all ten regions in Ghana, which is about 20% of the country's population (PPMED, Ghana, 1991). Tamale is the administrative headquarters of the Northern Region and by far the biggest town in Northern Ghana. Tamale is located in the Western Dagomba District of the Northern Region. The traditional state of Dagbon is the most populous and most ethnically homogenous of the four major traditional states that dominate the Northern Region. The population of the Western Dagomba District is 339998, with a population density of 43 inhabitants per square kilometre (1988). Tamale lies about 175 km east of 1° longitude west and 9° latitude north. This is towards the northern limits of the transition belt between the equatorial zone which has only one peak rainfall. About 80% of the people in the Northern Region depend on farming for their livelihood. Today, maize is the most widely grown cereal crop in northern Ghana. Rainfed agriculture is predominant in the Northern Region, and the potential for irrigation is limited. Increasing population, limited fertile area for crop production and ethnic confrontations describe the current situation in the North (Runge-Metzger and Diehl, 1993).
The survey area (Figure 3) included three districts in the Northern Region of Ghana -Tamale, Tolon-Kunbungu and Savelugu Districts - and is one of the parts of Ghana where storage of dried cassava chips is widespread. A number of factors were responsible for the decision to carry out the loss assessment study in the selected area of the Northern Region in Ghana. The most important reasons have been (a) the importance of dried cassava chips in this area of Ghana and (b) the presence and logistic support of the GTZ Post-Harvest Project in Tamale.
Figure 3: Survey area in the Northern Region of Ghana
Vegetation
Climate is the dominant factor in Ghana's physical environment. The natural vegetation of the study area is typical of Guinea savannah woodland, which is composed of trees of varying size and density dispersed in a ground cover of tall perennial bunch-grasses and associated herbs. Shea butter tree (Butyrospernum paradoxum), dawadawa (Parkia clapertiniana), mahogany (Khaya senegalensis) and neem (Azadirachra indica) trees are now the dominant tree species. Dawadawa and shea butter tree are protected for their economic value (Runge-Metzger and Diehl, 1993).
Soils
Soils are predominantly lateritic, and the texture is mainly silt or sandy loam. Their main characteristic is the presence of generally shallow depths below the surface of a more cemented layer of iron pan, through which rainwater does not penetrate easily. It therefore becomes water-logged in the rainy season but dries out completely during the dry season. Soil fertility is a major constraint for agricultural production (Runge-Metzger and Diehl, 1993).
Climate
The annual distribution of rainfall is bi-modal in the south of Ghana and other high rainfall areas, and uni-modal in northern Ghana. Annual variability is quite high resulting in considerable drought risks. The study area is characterised by distinct climate conditions such as one rainy season per year. Mean annual rainfall (see Table 4) is approximately 1100 mm and occurs over 95 rainy days. It builds up gradually from small rains in March/April to a maximum in August in the north, and then declines sharply, coming to a complete stop in mid-November when the dry Saharan winds usher in the harmattan season (see Figure 4). From December till February, the Northern Region is characterised by very distinct climate with relative humidity dropping to 15-26%, which enables the farmers to dry harvested cassava roots naturally. We observe from Figure 4 that the annual rainfall has predictable seasonal variability (Runge-Metzger and Diehl, 1993).
Table 4: Long-term annual precipitation at location Tamale, from 1990 -1995
|
Year |
Annual mean precipitation in mm |
|
1990 |
1060 |
|
1991 |
1580 |
|
1992 |
695 |
|
1993 |
1000 |
|
1994 |
1159 |
|
1995 |
1280 |
source: Regional Meteorological Office
Figure 4: Annual rainfall pattern per year for 1990-1995, Tamale, Ghana
High temperatures are experienced all year round but exhibit wide variations between day and night. Between November and February, maximum day temperatures can reach 33° C to 37° C and minimum night temperatures vary between 20° C and 22° C. The greatest amount of sunshine occurs in the period from November to February for about 8.5 hrs a day, while the lowest is in July and reaches only about four hours a day. The relative humidity of the area varies from 78% to 83% during the months of June to September and then gradually decreases to a low relative humidity of about 15 - 26% in January and in the dry season (Figure 5).
Figure 5: Relative humidity and temperature levels for Tamale in 1995
The cassava plant (Manihot esculenta Crantz) is a perennial shrub, ranging in height from one to five meters, with branching stems, green, pale or dark grey or brown in colour. The root crop is an ideal subsistence crop for the tropical world because it is well adapted to marginal soils, has the ability to tolerate environmental stress, gives relatively high yields compared to other staple crops, is an excellent source of carbohydrate and can be kept underground from 6 - 36 months after planting and is thus always available to the farmer. Cassava leaves contain about 7 -12% protein and are used as a vegetable in traditional soups and stews. The root itself is rich in carbohydrates (32%), vitamin C and calcium but poor in protein and other vitamins and minerals. Cassava roots are different from yams because they are not dormant organs and thus have very few biological functions (see Figures 6 and 7).
Figure 7: Harvest of tuberous cassava roots
Processing of Cassava
The purpose of processing cassava roots into a wide range of products is to control the deterioration of the food products. Apart from controlling losses, post-harvest processing decreases the toxicity of cassava by reducing its cyanogenic glycoside content. Cassava contains two cyanogenic glycosides, linamarin and lotostraulin, the former being present in much larger quantities, usually up to 90% of the total. The normal range of cyanogenic glycosides content, calculated in HCN, of cassava falls between 15 and 400 mg HCN/kg fresh weight. The content varies greatly among varieties and also with agricultural conditions. The tubers are detoxicated by hydrolysis of the cyanogenic glycosides and subsequent elimination of the liberated HCN. Contact between enzyme and substrates occurs when the tissues are mechanically damaged or there is loss of physiological integrity, such as during post-harvest deterioration. Most traditional food preparations appear designed to bring about the necessary contact by cell rupture when grating or pounding. This is then followed by elimination of HCN by volatilisation or solution in water. Equally, the processing or cooking which the cassava roots undergo prior to being consumed reduces these substances to a point that poisoning is prevented. (Lancaster et al., 1982; Hahn, 1988; Annor-Frempong, 1991; MOFA-GTZ, 1994).
Processing technologies for cassava in Ghana can be divided into three broad categories: (a) dry cassava products - fermented or unfermented; (b) fermented grated cassava and (c) starch and tapioca. The processing of cassava by the traditional techniques is often a very laborious and time-consuming occupation and is invariably carried out by women. Drying of cassava roots is the simplest method of preserving the root in the Northern Region of Ghana. Over 80% of the cassava produced remains on small-scale farms which range from 2 - 5 acres. The tubers are peeled, cut into pieces and sun-dried (see Figures 8 and 9). Drying is normally done on the concrete floor, roof tops, roadsides, or wooden platforms built over fireplaces in traditional kitchens. Leftover peels are fed to animals to prevent waste. The dried chips are normally pounded or milled by existing commercial plate mills to prepare kokonte. Kokonte, a flour product, is prepared from low cyanide varieties that are widespread in Ghana. Cassava chips are used solely for food preparation in Southern Ghana.
Figure 8: Peeling of cassava roots
The association of dried chip production with very dry climate zones may also be due to the requirements for drying. The quality of dried cassava chips processed by traditional methods is often poor, causing fungal or bacterial contamination. The flour is mixed with boiling water, prepared into a thick starchy paste and eaten with soup. In the grain-flour consuming areas of the North, it is used in combination with sorghum, maize or millet flour, either to improve the texture of the prepared food or as a cheaper supplement, and then referred to as tuozaafi (T.Z.), the traditional dish in the North of Ghana. It often supplements staple foods or even provides hunger relief where yields of other traditional staples are declining, such as in the North.
Other very popular cassava products in Ghana are fufu, gari, agbelima, agbelikaklo and yakeyake. In all these preparations, the roots undergo a fermentation process when they are immersed in water for some days. In the case of fufu the peeled or unpeeled roots are watered for some days, then dried in the sun and pounded into flour. The dried fragments possess a distinctive, pleasant taste due to the fermentation that takes place during the watering. In the West African preparation of gari or atieké, fresh roots are peeled, grated and then left to ferment, and the pulp is finally cooked and heated plates (Silvestre, 1989). Gari is the most commercialised product in Ghana because of a long shelf-life. The processing of agbelima is nearly the same as for gari but differs in being terminated after fermentation. If the dough is mixed with salt and moulded into balls, which are fried, it is referred to as agbelikaklo; and if these balls are only steamed it is called yakeyake (Hahn, 1988).
Traditionally the cassava root, after maturing, was left in the ground and harvested when needed. Increasing population and demand for more food dictates that more land area has to be cultivated. In some areas, the root crops cannot be kept in the soil for longer periods due to damage caused by cattle. Only about 7% of 150 farm households interviewed still perform this kind of traditional "in-ground storage" and leave the unharvested roots for about 12 - 36 months in the soil.
LEENGA
The majority of the interviewed farmers harvest the roots - when mature and dry them on the ground (38%) or on a raised wooden platform (55%), the LEENGA (see Figure 9). The drying structure is made of a wooden platform held on wooden poles about 1.5 to 2 m in height. The structure can remain for up to four to five years.
Figure 9: Drying structure for cassava chips - LEENGA
The main types of storage structures (see Figures 10, 11 and 12) commonly used by the 150 interviewed farmers are the traditional and improved KANBON (30%) and the NAPOGU (28%). Also indoor storage in jute sacks is performed by 22% of the farmers. Dried cassava chips are stored, on an average, for about six to eight months between January/February and July/August, depending on family consumption and cash needs. Cassava is mainly harvested as the last crop of a farm family and when the harmattan has set in for proper root-drying conditions (MOFA-GTZ, 1994).
Traditional KANBON (Kpachagliga)
The construction of a traditional Kanbon (see Figure 10) consists of a cylindrical basket built on a wooden or stone platform or stand which is only slightly raised 0.2 m above the ground. The basket is made of grass mats (zanamats) and varies in size. The basket can be between 1 - 2 m high and 1.5 - 2.5 m in diameter. The traditional Kanbon is covered with a grass thatched lid which is normally removable and serves as an inlet and outlet for cassava chips. In many cases, a small grass door in the basket is used for the same purpose. The inside of a Kanbon can be plastered with a mud cover or cow dung. The cassava chips are loosely arranged in the basket. The life span of such a structure varies, according to farmers, from three to five years.
Figure 10: Storage structure for cassava chips traditional KANBON
Improved KANBON
The improved version of the Kanbon (see Figure 11) is constructed in the same way as described above for the traditional version but the basket is raised well above the ground, approximately 0.5 to 1.1 m, on a wooden platform which allows for ventilation underneath. The poles can be made rodent-proof with metal sheets. The basket of an improved Kanbon varies in diameter from 1.5 to 2.5 m. The life span is estimated by farmers to be two to six years. The basket is sometimes coated with mud or cow dung on both the inside and outside.
Figure 11: Storage structure for cassava chips - improved KANBON
NAPOGU
This type of cylindrical store is the longer-lasting one and has a mud base covered by a thin layer of cement. It usually has a conical grass roof with an access hole just below it. Provided the foundation does not subside and crack, its life is considerably longer than that of the traditional woven basket stores. This construction (see Figure 12) consists of a cylindrical mud house and is covered by a thatched roof. Inside the structure there is commonly a wooden platform covered with zanamats on which chips are loosely arranged, and underneath there is space where fowl find shade or belongings are stored. The height of a Napogu varies considerably and is usually between 2 and 2.5 m without roofing. The diameter is between 2.5 and 3.5 m, and the life span of a Napogu is estimated by farmers between five and twelve years.
Figure 12: Storage structure for cassava chips - NAPOGU
Structure material
Poles for the platform and roofing are made of traditional wood from the shea butter tree (Butyrospermum paradoxum), neem (Azadiracta indica), dawadawa (Parkia clapertiniana) and mahogany (Khaya senegalensis). The zanamats are made of two different grasses -Andropogon spp. and Panicum maximum. The grasses for the roofs of the structures are Chrysopogon spp. and Cynodium longistaminata. The practice by which trees are cut to provide wood for the structures and rarely replanted is leading to environmental problems.
Maintenance of storage structures
Annual maintenance of storage structures includes removing zanamats and poles, replastering the store and re-roofing. About 69% of the 150 farmers interviewed claim that they clean and repair their structures before each storage season. Chemical treatments or special preparations for the wood and grass used are rarely undertaken. In some cases the wood is heat treated and the poles are put into fire and dried to make them more firm. But the majority of farmers choose firm and very dry wood for their structures as a prerequisite for proper storage management (MOFA-GTZ, 1994).
Most families have one or two structures of their own. It also appears that the choice of structure is determined by the local availability of raw materials and the social custom. Almost all farmers built the structures with the help of their family, friends or the community. The structures have varying capacities for storing chips, and on an average about 20 - 23 bags (1.3 to 1.5 tons) are stored per structure. The size of a bag varies considerably and the PPMED estimates that the average weight of one bag or sack is about 59 kg; however, we found that weight varies between 60 to 85 kg or even 95 kg for one bag. The life span of a structure depends very much on the maintenance throughout the usage and also on regular repairs. The majority of the storage structures are located inside the compound.
Storage protection
Treatment of dried cassava chips is rarely performed, and only about 3% of farmers claim to use chemicals, e.g. PHOSTOXIN (Aluminium phosphide) tablets. The only recommendation given by the Extension Service is the use of Actellic 50 or 100 (Pirimiphos-methyl); however, the Extension Service has not received any practical training on proper storage of chips. Experience with protection measurements for cassava chips from the research side is also lacking. The information on protection of maize produce is simply transferred to cassava. In most cases, the farmers perform sanitation and dry the cassava chips properly before storage. But some farmers observed that excessive drying of chips may even increase the possibility of insect attack, whereas less-dried chips are prone to mould infestation. During the storage period, farmers check their produce regularly and remove it for further sun-drying when heavy infestation is visible (MOFA-GTZ, 1994).
