Common names
Cassava, Brazilian arrowroot, tapioca [English]; manioc, tapioca [French]; yuca, mandioca, tapioca, guacamota, casabe, casava [Spanish]; maniok [German]; cassave, maniok [Dutch]; rogo [Hausa]; ketela pohon, ubi kayu, atau singkong [Indonesian]; mandioca [Portuguese]; kamoteng-kahoy, kasaba [Tagalog]; manyok [Turkish]; sắn, khoai mì [Vietnamese]; Ẹ̀gẹ́ [Yoruba]; لكسافا [Arabic]; কাসাভা (Kāsābhā) [Bengali]; 木薯 [Chinese]; מניהוט מצוי [Hebrew]; कसावा [Hindi]; キャッサバ [Japanese]; 카사바, 마니옥 [Korean]; മരച്ചീനി [Malayalam]; Маниок съедобный, кассава [Russian]; மரவள்ளி [Tamil]; มันสำปะหลัง [Thai]
- Product names: Cassava roots, cassava meal, cassava root meal, cassava chips, cassava pellets, cassava hard pellets
Species
Synonyms
Jatropha dulcis J. F. Gmel., Jatropha manihot L., Manihot aipi Pohl, Manihot dulcis (J. F. Gmel.) Pax, Manihot flabellifolia Pohl, Manihot leptopoda (Müll. Arg.) D. J. Rogers & Appan, Manihot manihot (L.) Cockerell, nom. inval., Manihot melanobasis Müll. Arg., Manihot palmata Müll. Arg., Manihot palmata var. leptopoda Müll. Arg., Manihot peruviana Müll. Arg., Manihot saxicola Lanj., Manihot tristis Müll. Arg., Manihot tristis subsp. saxicola (Lanj.) D. J. Rogers & Appan, Manihot utilissima Pohl (USDA, 2009)
Description
Cassava (Manihot esculenta Crantz) is a shrub grown in the tropics and subtropics for its underground starchy tuberous roots. Cassava roots, also called cassava tubers, are a major staple food for more than 800 million people in the world (Ecocrop, 2011; Lebot, 2009).
Morphology
The cassava plant is a woody shrub, reaching 2 to 4 m in height. The cassava tuber consists of the bark (outermost layer, 0.5-2% of the organ; easily removed by simple scratching), the peel (1-2 mm thick; 8-15% of the tuber; it contains most of the toxic cyanogenic glucosides) and the fleshy starchy parenchyma (83-92% of the tuber) which is the edible part of agricultural importance (Lebot, 2009; Tewe, 1992). Each plant has 5 to 20 starchy elongated tubers. Each tuber may be 20-80 cm long and 5-10 cm in diameter. Average tuber weight is between 4 and 7 kg but specimens up to 40 kg have been recorded (Ecocrop, 2011). The number and size of tubers is highly variable between cultivars and growing conditions (Ecocrop, 2011; Lebot, 2009). There are more than 7000 cassava varieties
Utilisation
Cassava tubers can be eaten boiled, mashed, deep-fried, etc. and there are many food products based on cassava, such as tapioca (cassava starch), a worldwide food ingredient, fufu (cassava flour boiled in water) and garri(fermented cassava mash), the two last popular foods in West and Central Africa. Cassava tubers also provide starch for ethanol production (Kuiper et al., 2007). Other cassava products include the finger-like leaves, which are consumed as vegetables or used as feed (see the Cassava foliage datasheet) and numerous by-products (notably pomace and peels) of the cassava processing industries (from starch, ethanol and cassava food production, etc.), which are also potential feeds (see the Cassava by-products datasheet). Cassava flour unsuitable for human consumption is also recycled as animal feed (Boscolo et al., 2002a). More than a third of cassava production is used for animal feeding (FAO, 2011):- Fresh roots, whole, broken or sliced
- Dried cassava chips: cassava chips sun-dried or artificially dried
- Cassava root meal: ground cassava chips
- Cassava pellets: ground and pelletized cassava chips. Hard pellets are particularly compact industrial pellets.
Distribution
A native to South America, cassava is now widespread throughout the tropics and subtropics, including Sub-Saharan Africa and South-East Asia. The main production areas are within 30°N and 30°S and from sea level to an altitude of 2000 m, depending on the latitude (Ecoport, 2009).
Optimal growth conditions are an annual average day-temperature over 18-20°C, annual rainfall ranging from 500 mm to 3500 mm, high solar radiation and light, well-drained and acid soils. Cassava may withstand light frosts at higher altitudes and cloudy conditions in the hot humid lowland equatorial belt. A hardy plant, cassava is highly tolerant to poor soil conditions, drought and pests (Vongsamphanh et al., 2004), but it does not grow well in heavy, rocky and gravelly soils. It is susceptible to waterlogged, saline and alkaline soils. Zinc deficiency should be avoided while very low P levels are well accepted.
Cassava root production has been increasing steadily since the 1960s and has surged since 2000 (increased 40% between 1997 and 2007, from 161 to 224 million tons). Its use in animal feeding has also increased from 25% of the crop in 1997 to 34% in 2007 (76 million tons). In 2010, 52% of cassava was produced in Africa, 33% in Asia and 15% in Latin America (FAO, 2011).
The production of cassava chips and pellets for animal feeding started in Thailand in the 1960s, fuelled by European demand for energy sources cheaper than cereal grains, which were then highly subsidized in the EU. Shipping expenses and European concerns about dust pollution motivated a shift from chips to pellets in the late 1960s and to hard pellets in the early 1980s. Cassava exports to Europe climbed until the mid-1980s (the Netherlands imported 45-50% of worldwide dried cassava), when the EU set importation quotas (FAO, 2001a). The European market gradually evaporated and was replaced in the mid-2000s by China, which now imports 85% of the dried cassava produced worldwide. Today, Thailand remains the major exporter of dried cassava (80% in 2009), far ahead of Vietnam (14%) (FAO, 2011).
Processes
Fresh cassava tubers, particularly high-quality ones, are very perishable. They deteriorate within two or three days of harvest and therefore must be processed quickly (Müller et al., 1975; Tewe, 1992).
Tubers intended for industrial animal feeding are sliced and dried, and then usually ground or pelletized. The technologies used at different scales of chip and pellet production are similar and cassava chips can be produced by simple techniques in the household or village as well as on a large mechanized scale. The selection of a technology depends on the amount of cassava to be processed, the availability of capital and labor cost, as well as the availability of relatively cheap energy (Hahn et al., 1992).
The first step is usually washing, followed by peeling. The roots are then sliced, either by hand or mechanically. Cassava chips may have different sizes and shapes, rectangular, cubic, thick sliced, depending on the slicing and drying methods. Drying may be natural or artificial. Sun-drying is done on concrete floors or on trays. Sun-drying is a very labor intensive operation, requiring about 35-40 laborers per hectare of drying floor. Chips dried on trays look better and are more uniformly dried than those dried on concrete floors. Artificial drying is done using static or moving bed dryers, or rotary dryers. Cassava chips can be sold directly, ground into cassava meal, or pelletized. During pelletizing, chips are heated and moistened and then forced into continuous die presses. Pelletizing results in a product that is 25-40% denser, more uniform, more durable, less dusty and easier to handle (Hahn et al., 1992).
Because peeling operations require time, alternative methods to produce chips and pellets without peeling have been developed. One such method consists in grating and chopping unpeeled tubers, mixing them with cassava foliage in a 4:1 ratio and passing the mixture through a pelletizer (Tewe, 2004).
In humid places where sun-drying is not easy, cassava roots can be ensiled alone (clean cassava roots + 0.5% salt) or mixed with rice straw or cassava leaves (Le Duc Ngoan et al., 2002; Premkumar et al., 2001; Kavana et al., 2005).
Forage management
Cassava is generally propagated by stem cuttings. However, under natural conditions as well as in plant breeding, propagation by seed is common and farmers in Africa are known to occasionally use spontaneous seedlings for subsequent planting (Lokko et al., 2007). Starch accumulation within the tubers occurs some 180-200 days after planting when they begin to thicken and store large quantities of starch. Because older tubers have the highest starch content, the best harvest period ranges from 9 to 24 months after planting. Cassava roots for animal feeding are commonly harvested from the 9th to the 12th month after planting (Kuiper et al., 2007; Régnier, 2011; Gomez, 1991). Harvesting is the most expensive part of cassava production. In order to improve tuber preservation, stems and leaves are cut two weeks before harvesting, leaving only a few centimetres of stems above ground. Uprooting must be done carefully because damaged tubers spoil readily (Kuiper et al., 2007). In 2009, the average worldwide tuber yield was 13 t/ha (FAO, 2011).
Environmental impact
Most cassava is produced by smallholder farmers living in marginal and fragile environments, and particularly on erosion-prone, acid and infertile soils. This ability to produce on poor soils, where most other crops would fail, has given cassava a reputation as a safeguard against food scarcity. However, there are serious environmental concerns about cassava production (FAO, 2001b). For the environmental impact of cassava processing, see the Cassava by-products datasheet.
Soil nutrient depletion
Cassava production can be detrimental to soil fertility through crop removal of nutrients. Due to the low value of cassava products, the application of manure and chemical fertilizers, which could easily correct nutrient depletion, may not be economically justified or affordable for smallholders. However, it should be noted that, at current yield levels, soil nutrient depletion by cassava is lower than depletion caused by other crops (FAO, 2001b).
Erosion
Cassava production can result in serious erosion when the crop is grown on slopes or on light soils. Good agronomic practices (adequate fertilizer, closer plant spacing, planting on contour ridges, intercropping, reduced tillage), used alone or in combination, can reduce erosion by 50-90%. Properly managed cassava production on slopes does not necessarily cause erosion (FAO, 2001b).
Water pollution
It is considered unlikely that cassava production results in water pollution, as it is grown mainly by poor farmers who apply no or very low rates of fertilizers, pesticides and herbicides. However, this may change in the future (FAO, 2001b).
Biodiversity
Cassava production does not seem to have had widespread effects on biodiversity, though some local situations may merit attention, such as deforestation in the north-east of Thailand or the competition with native cassava species in Latin America (FAO, 2001b).
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