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The cassava sub-sector analysis

A schematic representation of the cassava production to consumption system in sub-Saharan Africa is shown in Figure 1. Most of the production takes place in small farms with inputs covering the whole spectrum for agricultural production in Africa. Imported inputs consist of small hand tools used by small farmers, tractors, machinery, fertiliser and other agricultural chemicals, used mainly by medium and large-scale farmers. Large-scale agro-industries, which produce fertiliser, agricultural chemicals, and farm production machinery (tractors, ploughs, etc.), are widespread in SSA. Small scale and artisan agro-industries that produce hand tools, and processing machinery are more important in the cassava system, and provide a link to the industrial sector.

Roots are generally transported by head load and where the road network permits, by trailers and small trucks. Cassava roots are processed into a wide variety of products for human and industrial consumption, ranging from simple boiling, to fermented products and beverages. Most of the products are consumed domestically within the countries in which they are produced. However, there is a small but growing export trade in dried cassava chips and other industrial products.

Agricultural policies and infrastructure constraints variably affect the cassava sub-sector at different stages, and the system contributes significantly to employment creation, income generation and has an impact on the environment.


Regional production trends and use of farm resources

Cassava production is generally influenced by climatic, biological, technical, economic, and institutional or political factors. Current sub-regional production is estimated to be 28 million metric tons. The relative importance of the crop varies among member countries. The main cassava producing countries in the sub-region are D. R. Congo (21m MT) followed by Uganda (4.0m MT) and Madagascar (2.5m MT). Smaller producers are Kenya (0.86m MT), Burundi (0.6m MT) and Rwanda (0.4m MT) although, in recent years, production in all three latter countries has begun to increase, associated with greater national attention to the crop. The D. R. Congo moved from being the largest to the second largest producer after Nigeria. Most of the production increases have been due to increases in area under cultivation rather than increases in yields. This expansion in cultivated area is replacing fallow as the crop is planted just before land is allowed to fallow. Out of the total representative villages surveyed during COSCA, 53% reported that cassava production was increasing in response to food security (63%), market availability (12%) and population growth (10%) while 47% thought it was not. Major reasons given by farmers for abandoning cassava varieties were ranked as: low storage root yields, late bulking, poor in-ground storability, disease/pest susceptibility, high HCN and low yield of planting material. Market related factors therefore drive farmers to increase cassava production.

Cassava is replacing other food crops even though it is generally grown in mixed cropping. Only 20% of fields visited were found in pure stands. Maize, legumes (peas/beans), sweet potato, and sorghum/millets were noted as main crops commonly inter-cropped with cassava. Average cassava root yield in the region is 10.5 tons/ha. Plant density, market accessibility, proportion of cassava marketed, age at harvest, demographic pressure are the key determinants of cassava root yield. Eighty per cent of the total cassava output is processed and only 20% are used in fresh form. The main cassava products include cassava chips/flour and fresh root.

Cultivation is generally thought to require less labour per unit of output than most other major staples. Any expansion of production would lead to increase labour productivity. Though cassava is able to grow and give reasonable yields in low fertility soils, adequate fertilisation is needed for the crop to reach its maximum production potential. Cassava requires relatively little nitrogen; however, phosphorus and potassium are important nutrients needed to maintain high yields in a continuously cultivated area. Potassium fertilisation is essential because deficiency leads to lower dry matter and starch content, and consequently a higher cyanogenic potential in the storage roots.

Potential and prospects

Food security, low cost nutrients and famine mitigation: Cassava is a major source of dietary energy for low-income consumers. It plays a food security role in providing a stable food base in areas prone to drought, famine and during periods of civil. Cassava is predominantly used as food with small amounts for agro-industrial livestock feeds and starches production. For fresh consumption, roots are boiled or eaten raw. The most common processed product is flour made from fermented or non-fermented dried chips of the peeled storage roots, which is then reconstituted to pastes as required. Leaves of cassava are used as a fresh vegetable in several countries, often providing protein, vitamins and minerals in diets which otherwise are nutritionally marginal. Processing technologies in the region are poorly developed.

Farmers in Uganda, Tanzania and D.R. Congo rate cassava as the most important crop while maize is the choice crop in Burundi and Kenya. With changes in technology, policy and prices, cassava could play a greater role in improving the quality of urban diets by increasing supplies of the low-cost staple foodstuff in convenient forms. A major constraint to expansion of utilisation was the lack of understanding of cyanogenesis, a mechanism that has now been elucidated.

The recent erratic seasonal rainfall and failure of grain crops have stimulated farmers to give more attention to the potential of cassava to mitigate the effects of famine. It can grow and produce some harvestable product in marginal conditions due to its inherent hardiness making it a highly appropriate crop for risk aversion. To exploit the potential of cassava in viable farming enterprises rather than a crop of last resort, would need greater attention in the broad area of post-harvest including marketing, primary processing and product development. By stimulating consumer demand for cassava-based food products and satisfying their immediate domestic food needs, farmers will have confidence that there are assured outlets for their produce, and associated cash earning opportunities,

Cash income and foreign exchange earner: Studies have shown that the proportion of cassava sold by small-scale producers is positively correlated with the proportion of fields owned by women, the degree of use of purchased inputs, and the proportion of cassava processed before sale. In cassava producing areas, food crops contribute about 40% of household cash income, industrial crops and non-farm activities about 25% each, while livestock contributes about 10%. About 26% of cash income from all food crops in cassava growing households were derived from sale of cassava. This proportion was exceeded only in rice growing households where 29% of food cash income was derived from rice sales. Cassava cannot be regarded only as a non-tradable subsistence crop but as the main source of cash income for the producing households with an equity role. Export opportunity and import substitution possibilities for cassava flour and industrial starch are available; however, its potential as a foreign exchange earner needs to be carefully assessed based on the comparative advantage of the products.

Environmental effects of cassava

Continuous cultivation of cassava is widespread in the non-humid and highland zones and where fallow is used, farmers use the crop to close a rotation cycle. The primary response to the growing population pressure in cassava growing areas of SSA is still the expansion of area under cultivation. When fallow periods are reduced below a critical minimum, the soils degrade resulting in breakdown in soil structure, decline in organic matter status, nutrient loss, increased acidity and aluminium toxicity, water logging, runoff and erosion. Cassava may delay intensification by enabling farmers to produce a crop under marginal circumstances instead of shifting to crops that require higher production inputs. On the other hand, where there is stable demand, cassava could be grown intensively as a cash crop for urban consumers.

Infrastructure and market access

Rural infrastructure, comprising rural roads, markets, irrigation systems, water supply, health and educational facilities, are basic to quality of life in rural areas. Although they all have a critical role to play in any agricultural development strategy, rural roads are fundamental for agricultural development.

The rural transport system in most of SSA is inadequate and existing network is in poor state of repairs requiring substantial rehabilitation. The COSCA data shows that only 20% of villages in cassava growing areas are accessible by motor vehicle, with the proportion being significantly lower in Burundi, Uganda and Congo. In over 70% of villages, produce must be head-loaded to market, with distances of more than 10 km in 11% of all villages. In Congo, the second most important producer of cassava in SSA, farmers in over 40% of villages must head-load their produce over 10 km to market.

Post-harvest handling technologies

Thirty percent of the cassava produced in Africa is for fresh consumption. Shelf life of fresh cassava roots rarely exceeds two days. The high perishability of harvested cassava and the presence of cyanogenic glucosides in cassava require immediate processing of the storage roots into more stable and safer products. Storage and packaging technologies to extend shelf life will contribute to increasing cassava root availability and reliability, stabilising prices and facilitating export. The extent to which the potential market for cassava may be expanded depends largely on the degree to which the quality of various processed products can be improved to make them attractive to various markets, local and foreign, without significant increases in processing costs.

There are two main channels for farmers to market their storage roots. Traders purchase the standing crop (field purchase) or already harvested crop (home purchase) which are conveyed to markets for sale. Otherwise traders visit periodic markets to purchase storage roots directly from producers who would have transported them there. Direct consumer sales are not preferred since shelf life rarely exceeds 2 days. Quick sales avoid spoilage.

Processors are mainly located in rural areas and obtain their supplies of storage roots in the same way as traders. Traditionally, cassava roots are processed by a variety of methods into many different food products, depending on locally available processing resources, local customs, and preferences. They include cooked fresh roots; cassava flours (fermented or unfermented); granulated roasted cassava (gari); granulated cooked cassava (attieke, kwosai); fermented pastes; sediment starches; drinks (with cassava components); leaves (cooked as vegetable); and medicines. Flours are the most widely used cassava product and are processed in a variety of ways. Those form unfermented cassava roots are more common in areas where sweet cassava varieties dominate. Over 50% of all villages have some form of cassava processing centre, using machinery such as mills. Mechanised processing is positively associated with population density and improved access to market.

Simple processes allowing farmers to convert the highly perishable cassava roots into dry, easily stored, and freely traded commodities are available. Improved cassava processing equipment has been designed and tested by research institutions for use at farm and village levels. The equipment reduces post harvest losses, increase labour productivity, and improve product quality.

Gender role in cassava trade and processing

Both sexes are equally represented in trading, but women, and to lesser extent children, dominate in cassava processing. As opportunities for commercialization increase, the number of women involved in processing increases. Growth in cassava production is therefore likely to provide increased employment opportunities for women. However, there is a tendency that as mechanised processing equipment are acquired, men's involvement in cassava processing tends to increase, as they often control and operate these machines. Women may therefore loose some of the benefits of increased employment, as they loose control of some of the income. Steps need to be taken to ensure that this does not happen, e.g. by increasing the access of women to credit for acquisition of post-harvest machinery, and training them to properly operate the equipment. This means that the needs of women should be kept in mind even at the equipment design stage

Regional research and development issues

Post-harvest utilization and commercialization

More than half of the world cassava production comes from Africa where it is used almost exclusively as food. Increased use of cassava as a low-cost energy food, in animal feed and other industrial applications will motivate farmers to expand production. The potential market expansion would depend on the quality of various processed products for various markets without significant increases in processing costs. Traditional post harvest processing/handling technologies are labor intensive requiring the use of labor saving equipment and tools to reduce the drudgery and cost of processing while improving the quality of processed products.

The utilization of cassava in animal feed, starch, confectionery, textile, paper and pharmaceutical industries are yet to be adopted in Africa because of unreliable supply. Longer shelf life of fresh cassava and extended storage of dried cassava (chips/flour) will aggravate the problems caused by post-harvest pests. These include the larger grain borer (LGB) and root rots. Fungi are also known to infest cassava chips during processing and handling, in the field or during storage; they may lead to the formation of mycotoxins making the chips unable to meet trade and health standards.

Lack of well adapted varieties

COSCA data indicate that farmers are abandoning old cultivars and introducing new ones due to their need for better varieties, but also highlights the danger of loss of genetic diversity. While it is more evident that cassava is expanding in the mid-altitude and into the semi-arid zones, the available improved germplasm is mostly adapted to the lowland humid tropics. Germplasm adapted to these other agro-ecological zones is needed. Expansion of the utilisation of cassava for new industrial uses requires germplasm with high yield and specific quality traits for specific end-uses.

Insufficient and poor quality planting material

Cassava production is dependent on a supply of vegetative planting materials. The multiplication rate of these materials is very low in comparison with grain crops, which are propagated by true seed. Cassava planting materials are bulky and highly perishable as they dry up within a few days after harvest, and hence their multiplication and distribution are expensive relative to conventional grain-based seed services. The yield stability and development of cassava is highly dependent on the quality of planting materials, and there is evidence that the initial use of healthy cuttings is a very important factor in the subsequent attainment of good yields. Cuttings with low vigour, infested/infected by pests and diseases, often limit cassava production. Biomass production is low in dry agro-ecosystems and production of planting materials in sufficient quantities is a major restriction to the widespread and rapid adoption of the crop or a variety.

Plant pests and diseases

Historically, cassava had few serious pests and diseases in Africa. However, the situation changed as cassava cultivation intensified and exotic pests were introduced. The major cassava pests include relatively few phytophagous arthropods, plant pathogens, and weeds compared to the pest complex found in the neotropics. Together, these species could reduce cassava production by as much as 50%. The most severe pests were the exotic species accidentally introduced into areas where the local germplasm is susceptible to attack, where effective natural enemies/antagonists are absent, and where a tradition of practices to cope with the introduced pests had not evolved. In addition, pest problems are being created where intensification of cassava production erodes the environmental stability inherent in balanced agro-ecosystems.

Shortening fallow periods and declining soil fertility

The predominance of different fallow systems, namely long fallow, fallow, and continuous cultivation, varies among villages, depending on soil fertility status and on pest/disease, market, and demographic pressures. It is often reasoned that as fallow periods shorten, cassava will increasingly replace crops which demand higher soil fertility and production labour. Although cassava is well adapted to growing under continuous cultivation, it is not as frequently grown under that system as other major staples.

The farmers' ability to respond to declining fallow periods due to demographic, market, pests/disease, and other pressures by replacing more susceptible crops with cassava is constrained by its long cropping cycle. Cassava can be harvested from 6 months from planting, but most available local varieties do not attain maximum yield before 22-24 months. Currently improved varieties attain their maximum yield at 12-15 months. Under intensive cultivation where the fallow period is often less than one year, such varieties are not ideally suited because they may be harvested before they attain maximum yield. Early-bulking varieties are not likely to reduce this pressure unless they are combined with agronomic practices for greater water and nutrient-use efficiency. Shortening fallow periods require varieties selected for efficient nutrient assimilation, and for better ability to be intercropped with legumes or other soil fertility conservation strategies.

Availability of reliable data

The COSCA study has provided a wealth of first hand information on cassava production, processing and constraints. Other regional research projects and networks are collecting complementary baseline data. Available information should be consolidated in an electronic database accessible to all interested parties. The consolidation process will reveal information gaps that need to be addressed.