Strategic environmental assessment (2024)

Cassava in Africa, Asia, Latin Americaand the Caribbean

Table 1 shows the area and dry matter (DM) production of themajor food crops worldwide. In terms of dry matter production, cassava is thefourth most important crop in SE Asia, seventh in Asia, fifth in Latin Americaand the Caribbean (LAC), second in Africa, and the most important crop inSub-Saharan Africa. Area planted to cassava (FAOSTAT, 1999) is highest in Africaat 10.10 million ha (62% of world total), followed by Asia at 3.48 million ha(21%) and LAC at 2.70 million ha (17%), for a total area of 16.28 million haworldwide (Figure 1).

Africa accounts for 51%, Asia 29% and LAC 20% of worldproduction. Fresh root yields are highest in Asia at 13.7 t/ha, followed by LACwith 11.9 and Africa with 8.4 t/ha. The higher yields in Asia are partially dueto a near absence of diseases and pests (except in India), and relativelyintensive crop management, which in a few isolated areas (Tamil Nadu of India)includes irrigation and high rates of fertilizers.

Production environments

Cassava is produced between 30^o north and southlatitudes, and near the equator up to an altitude of about 1800 masl. Because ofthe crop's tolerance to drought and low soil fertility, it is generally producedin marginal areas with poor soils, and/or high risk of drought.

Cassava grows best in areas with a mean temperature of25-29°C, and a soil temperature of about 30°C; below 10°C theplant stops growing. While the crop grows best in areas with an annualwell-distributed rainfall of 1000-1500 mm, it can tolerate semi-arid conditionswith rainfall as low as 500 mm, and may have a competitive advantage over othercrops under those conditions. Cassava can grow on a wide range of soils, but isbest adapted to well-drained, light-textured, deep soils of intermediatefertility. Under high fertility conditions top growth may be stimulated at theexpense of root growth. Optimum soil pH is between 4.5 and 6.5. The crop doesnot grow well in poorly drained soils, gravelly or saline soils, or in soilswith a hardpan (Onwueme and Sinha, 1991).

Soils

Table 2 shows the distribution of cassava growing areas withrespect to the various soil orders of the US soil classification system. In Asiaabout 55% of cassava is cultivated on Ultisols, which are characterized by lowpH (but not low enough to limit cassava growth) and low nutrient content. Of themajor plant nutrients K is usually the most limiting, especially if cassava isgrown for many years on the same soil. Another 18% of cassava in Asia is grownon Inceptisols, mainly on Java island of Indonesia. These soils are also low inN, P and K, but which of these is the most limiting depends on the local soilcharacteristics. Another 11% of cassava in Asia is cultivated on Alfisols,mainly on Java. These soils tend to have a high cation exchange capacity, arelatively high pH and high fertility. Because of high pH and high levels of Caand Mg, cassava may suffer from micronutrient deficiencies, especially Zn andFe. Finally, about 9% of cassava is grown on Entisols, again mainly on Java. Onthese soils cassava production may be limited by an inadequate supply of N andK, or, in very sandy soils, Zn.

Figure 1. Distribution ofcassava in the world. Each dot represents 1000 ha.

Source: CIAT, 1995.

Table 1. Area and production (on dry weight basis) ofmajor food crops in various regions of the world in 1997.

¹⁾ On dry matter basis, assuming thegrains to contain 86% DM, cassava 38%, sweet potato and potato 20%, andsugarcane 26%.

²⁾ Includes Brunei, Cambodia, Indonesia, Laos,Malaysia, Philippines, Singapore, Thailand and Vietnam.

See Also

Grow Cassava for Its Edible Roots or as an OrnamentalHow many bags of garri can a ton of cassava produce?How many pounds of grain can one acre produce? - Good in Every GrainCassava Harvesting and Processing

³⁾ Sub-Saharan Africa includes Angola, Benin,Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad,Comoros, Dem Rep of Congo, Rep of Congo, Cote d'Ivoire, Dibouti, EquatorialGuinea, Ethiopia, Gabon, Gambia, Ghana, Guinea, Guinea-Bissau, Kenya, Lesotho,Liberia, Madagascar, Malawi, Mali, Mauritania, Mauritius, Mozambique, Namibia,Nigeria, Niger, Rwanda, Reunion, Sao Tome and Principe, Senegal, Sierra Leone,Somalia, Sudan, Swaziland, United Rep. of Tanzania, Togo, Uganda, Zambia andZimbabwe.

Source: FAOSTAT, 1999.

Table 2. Soils on which cassava is produced in LatinAmerica and Asia and their principal constraints for the crop.

¹⁾ Based on a total cassava area of2,512,000 ha in Latin America
²⁾ Based on a total cassava area of3,582,000 ha in Asia
Source:

¹⁾ CIAT,1983
²⁾ Howeler, 1992.

In sharp contrast to Asia, in Latin America and the Caribbeancassava is grown on almost equal proportions of Ultisols, Alfisols and Oxisols,with lower proportions of Entisols, Inceptisols and Mollisols. Brazil accountsfor 70% of the cassava growing area in LAC and most of these soils are found inthat country. Unlike in Asia, in LAC cassava is grown extensively on Oxisols,which are generally characterized by low pH (4.2-6.0), high levels ofexchangeable Al and very low nutrient contents. In only a few areas, mainly theEastern Plains of Colombia, will cassava benefit from small applications oflime, principallly as a source of Ca and Mg. The Oxisols also tend to be verylow in P and K, the former generally being the most limiting nutrient during thefirst year of cassava cultivation, while K becomes more important in subsequentplantings on the same soil.

For Africa similar data are not yet available. However,according to the Collaborative Study of Cassava in Africa (COSCA) (Carter etal., 1992), about 54% of the cassava growing areas are constrained by highacidity and low soil fertility. Since "high acidity" is defined as a soil withpH<5.5, it is unlikely that acidity is the real limiting factor, as cassavais known to tolerate pH values as low as 4.0-4.2 and high levels of exchangeableAl (up to 85% saturation) (Howeler, 1991b; Asher et al., 1980). Mostlikely, cassava production in Africa is constrained by low soil fertility, asmost cassava is grown on Oxisols, Ultisols and Entisols. The same COSCA study(Carter et al., 1992) reports that 10% of the cassava area in Africa isconstrained by shallow soil depth or texture, and another 4% by poordrainage.

Climate

Tables 3 and 4 show the distribution of cassava-growing areasin the three continents according to climaticzones[13]. In Latin America almost 30% ofcassava is grown under subtropical conditions, sometimes with frost during thewinter, which may kill the above-ground growth; in Asia this is about 15% and inAfrica only 10%. In both Latin America and Africa about 20% of cassava is grownin the highlands with year-round cool temperatures of <22°C; in Asiaalmost no cassava is grown at high elevations.

Latin America and Africa are similar in terms of dry-seasonlength, with 40-45% of cassava grown in both the humid and seasonally dry zones,and with 10-15% in the semi-arid zone. According to Table 4 Asia has 26% of thecassava area in the semi-arid zone, but that is partially due to a widerdefinition of semi-arid climates used in Table 4 than in Table 3. According tothe latest agro-ecological zone classification (Peter Jones, personalcommunication) practically no cassava in Asia is grown under semi-aridconditions, while this same classification used in LAC and Africa shows ratherlarge areas (about 20-30%) in this zone, mainly in NE Brazil and in Mozambique(Appendix 1).

Table 3. Cassava distribution in Latin America andAfrica by climatic conditions.

¹⁾ Based on total cassava area of 1,816,000 ha in LA and 7,992,000 ha in Africa
²⁾ Mean growing season temperature: Lowland >22°C; Highland <22°C
³⁾ Length of dry season (<60mm rain): Humid 0-3; Seasonally dry 4-6; Semi-arid 7-9; Arid 10-12 months
⁴⁾ Seasonality (difference between hottest and coldest month): Tropical <10°C; Subtropical >10°C
Source: CIAT, 1989.

See Also

More cassava for less time - World

Table 4. Cassava distribution in Latin America and theCaribbean (LAC) and in Asia by climatic zones.

¹⁾ Altitude (masl): Lowland < 1000;Highland > 1000
Length of dry season (<60mm rain): Humid: 0-3; Subhumid4-5; Semi-arid >5 months
Latitude: Tropics: between 20^oN andS

²⁾ Based on 2,781,000 ha in LAC and 3,921,000 ha inAsia
Source: Norel, 1997.

Elevation and topography

About 80% of cassava in Africa is grown in the lowlands andthe remaining 20% in the highlands, mainly in tropical highlands in Angola andthe Great Lakes Region of Uganda, Rwanda, Burundi and northern Tanzania. InAfrica some cassava is also found in subtropical highlands, mainly in Zambia andMadagascar. In these areas cassava may be found on steep slopes of 10-50%(Carter et al., 1992).

In Asia very little cassava is found at elevations above 1000masl (Table 4). Most is grown on gentle slopes of 0-10%, but in southern China,north Vietnam and on Java the crop can be found on steep slopes of 15-50%.Especially in Indonesia these areas are usually terraced and cassava is oftenintercropped with other food crops on narrow strips of terraced land. In Chinathe crop is sometimes planted on steep slopes as an intercrop between youngtrees in areas recently reforested (Henry and Howeler, 1996).

In Latin America about 417,000 ha of cassava are found in thehighlands. Cassava grown in the tropical highlands is found mainly in the Andeanzone of Colombia, Ecuador and Peru, as well as in Central America; that grown inthe subtropical highlands is found mainly in southeast Brazil, eastern Paraguayand northern Argentina. In the highlands, cassava is often cultivated on slopesup to 40%, and occasionally on steeper slopes. In the southern states of Brazil,such as Sao Paulo, Parana and Santa Catarina, cassava is often grown on gentleslopes of <10%, but because of intensive mechanical land preparation seriouserosion can occur under those conditions. Where land is prepared by hoe oroxen-drawn plow, land preparation tends to be less intensive and fields aresmaller, resulting in less serious erosion.

Cropping systems

In much of the African lowlands cassava is grown inslash-and-burn systems, usually as the last crop in a rotation, after maize,cowpea and upland rice, and before the plot is returned to bush fallow. Cassavais generally the last crop in the rotation because it will still produce areasonable yield on nutrient-depleted soils. This is most likely a significantpart of the reason for very low cassava yields in Africa. In the Africanhighlands cassava is generally grown after short-term fallows.

Cassava is mainly grown intercropped with maize, yam, peanutor cowpea in West Africa, or with banana, maize, cowpea and beans in East Africa(Ezumah and Okigbo 1980); C. Wortman, personal communication). In westernNigeria cassava is grown together with yam, maize and egusi melon on the samemound, while in other areas crops are grown in separate rows (Okeke, 1984). InSierra Leone cassava is often intercropped with upland rice, planted 4-6 weeksafter cassava (Dahniya et al., 1994).

Cassava farmers in Africa seldom apply any chemicalfertilizers to cassava (or most other crops) even though trials have shown thatcassava is highly responsive to fertilizer applications (Richards, 1979; FAO,1980). Instead, most farmers rely on natural fallows to restore soil fertility;they may apply small amounts of animal manure or ash, but usually to theintercrop. Soil preparation is mainly done by men, using a short-handled hoe insouthern Nigeria, while in the northern part of the country farmers use oxen forplowing. In Tanzania cassava is planted on ridges and in Uganda without ridges.Planting, weeding and harvesting is done mostly by women.

In Central America and the Andean zone of South Americacassava is often planted after short (2-4 year) fallows. After slashing andburning of the fallow vegetation, cassava is planted for 2-3 years withoutfertilizer or manure input, until the soil's fertility has been exhausted andlow yields do not permit further cultivation. However, the fallow period isoften too short and the native soil fertility too low to allow for adequateregrowth of vegetation to restore soil fertility. If cassava cultivation is alsoassociated with serious erosion, then soil fertility in these areas cannot berestored, and farmers are caught in a downward spiral of productivity decline,leading to ever increasing poverty.

In the mountainous areas of Central America and the Andeanzone, cassava is usually grown intercropped with maize, cowpea or beans. Theintercrops may receive some fertilizers or manure, but these are seldom appliedto cassava, as the low value of the crop does not justify expensive inputs offertilizers. In Cauca Department of Colombia farmers are now applying ratherhigh amounts of chicken manure, with good results.

Along the eastern coast of Brazil and in extensive areas ofthe Northeast, cassava is mostly grown by smallholders under very marginalconditions of drought and low and declining fertility. In the southern states ofSao Paulo, Parana and Santa Catarina, climate and soil conditions are morefavorable and management is more intensive, leading to higher yields. In Brazilthe crop is grown mainly in monoculture or intercropped with maize, beans orcowpea. In many areas in the South, fields are plowed by tractor followed byfurrowing. Fertilizers (P and K) are often applied at the bottom of the plantingfurrow, after which they are covered with a little soil before placing thestakes horizontally in the furrow and filling over with soil.

Table 5 shows the details of the prevailing cassava croppingsystems used in the various countries of Asia. Even within countries there maybe marked differences among regions. Crop management is mainly determined by thesize of farms and the availability of labor. In countries with comparativelylarger farms, such as Thailand and Malaysia, and on large plantations inIndonesia and the Philippines, cassava is generally grown in monoculture, andland preparation is by tractor. In areas of small farms, such as Kerala state ofIndia, Java island of Indonesia, northern Vietnam and southern China (Henry andHoweler, 1996), land preparation is usually by hand using a hoe, or by ananimal-drawn plow. In many cases cassava is intercropped with peanut or maize,and occasionally with sweetpotato or watermelons (China). In India and Indonesiafarmers tend to apply 5-20 tonnes of cattle or chicken manure, while in northVietnam and China farmers apply 3-7 tonnes of pig manure, often mixed with ricestraw. Fertilizers are commonly applied at high rates in Malaysia and Tamil Nadustate of India, but at low rates in Thailand, Indonesia (mainly N), China andVietnam (Pham Van Bien et al., 1996). Little or no fertilizer is used inKerala state of India, in the Philippines and in central Vietnam. In Keralastate short-duration (6-7 months) varieties are now often planted after rice inlowland fields, producing very high yields due to adequate soil moisture andbetter fertility. This, and the very intensive high input systems used in TamilNadu, result in very high yields (average of 22 t/ha) of cassava in India (Nayaret al., 1995).

[13] Tables 3 and 4 do notcorrespond, because they include different areas (only Latin America inTable 3 and Latin America and the Caribbean in Table 4) and use somewhatdifferent classification systems. The authors consider that consensus about thebest criteria for a useful cassava agro-ecological zone classification isurgently needed.