Cassava (Manihotesculenta) is a shrub or small tree up to 5 m tall, cultivated for its edible root tubers which are widely used as a staple food source. Stems brittle, branching dichotomously, often blueish-grey when young; whitish watery sap present. Leaves up to 15 × 25 cm, deeply divided into 3-7 oblanceolate lobes, dark green above, paler blue-green beneath, almost hairless or slighly pubescent near the midrib; margin entire; petiole up to 25 cm long, often reddish-purple. Inflorescences in lax terminal heads, 2-11 cm long.Flowers unisexual in the same inflorescence, greenish tinged orange-red and often with purplish veining.Fruit ellipsoid to subglobose, up to 17 × 15 mm, greenish, finely wrinkled, six-winged.
Raw cassava is 60% water, 38% carbohydrates ,1% protein. Cassava, like other foods, also has antinutritional and toxic factors. Of particular concern are the cyanogenicglucosides of cassava (linamarin and lotaustralin). On hydrolysis, these release hydrocyanic acid (HCN) . The presence of cyanide in cassava is of concern for human and for animal consumption.
Biofuel: In many countries, significant research has begun to evaluate the use of cassava as an ethanol biofuel feedstock.
Animal feed: Tubers being grated; a close-up of the product; drying on road to be used for pig and chicken feed. Cassava tubers and hay are used worldwide as animal feed.
Laundry starch: It is also used in a number of commercially available laundry products, especially as starch for shirts and other garments. Using manioc starch diluted in water and spraying it over fabrics before ironing helps stiffen collars.
Cassava is a tropical root crop, requiring at least 8 months of warm weather to produce a crop. However, under adverse conditions such as cool or dry weather it can take 18 or more months to produce a crop.
Propagation by seed: For agricultural purposes, cassava is propagated exclusively from cuttings because seed germination is usually less than 50 percent. Seedlings are raised from seed only for the purpose of selecting seedlings with fewer and smaller roots than those of the parents. Botanically seeds are used only for breeding purposes.
Propagation by cuttings: Propagate cassava by planting segments of the stem. Cut stems into 9-30 cm lengths; be sure to include at least one node. Segments can be buried vertically with 8-15 cm in the ground. The selection of healthy, pest-free cuttings is essential. Stem cuttings are sometimes referred to as ‘stakes’. In areas where freezing temperatures are possible, plant cuttings as soon as the danger of frost has past. Cuttings can be planted by hand or by planting machines. Hand planting is done in one of three ways: vertical, flat below the soil surface or tilted. Under low rainfall conditions, vertical planting may result in the desiccation of the cuttings, while in areas of higher rainfall; flat-planted cuttings may rot. In general, flat planting 5-10 cm below the soil surface is recommended in dry climates and when mechanical planting is used. Germination seems to be higher; tubers tend to originate from a great number of points and grow closer to the surface of the soil, making better use of fertilizers applied on the surface and also making harvesting easier.
Vertical planting is used in rainy areas and tilted planting in semi-rainy areas. Observing the polarity of the cutting is essential in successful establishment of the planting. The top of the cutting must be placed upright. Typical plant spacing is 1m by 1m. Cuttings produce roots within a few days and new shoots soon appear at old leaf petiole axes on the stem. Early growth is relatively slow, thus weeds must be controlled during the first few months. Although cassava can produce a crop with minimal inputs, optimal yields are recorded from fields with average soil fertility levels for food crop production and regular moisture availability.
Responses to macro-nutrients vary, with cassava responding most to P and K fertilization. Vesicular-arbuscular mycorrhizae benefit cassava by scavenging for phosphorus and supplying it to the roots. High N fertilization, more than 100 kg of actual N/ha, may result in excessive foliage production at the expense of storage root development. Fertilizer should only be applied during the first few months of growth.
In moist soil, sprouting takes place within the first week after planting. Within a month of the beginning of planting, the substitution of new cuttings to replace those that did not sprout is still possible. Cassava is grown mainly as a cash crop and farmers may for ten years or more grow cassava on the same land. However, if the price of cassava roots drops, the farmers may shift to another crop (e.g., sugarcane, maize or sorghum) until cassava again becomes the more profitable crop.
Pests And Diseases
Insects, diseases and other pest: In many regions, the cassava plant is not normally affected by diseases or pests. However, in others it may be attacked by the following:
- Virus diseases. Mosaic, the brown streak and leaf curl of tobacco may attack leaves, stems and branches. Many parts of Africa harbor these diseases and attempts are being made to select resistant varieties.
- Bacterial disease. Bacteria such as Phytomonasmanihotis (in Brazil), Bacterium cassava (in Africa) and Bacterium solanacearum (in Indonesia) may attack roots, stems or leaves of cassava plants.
- There are kinds which attack roots, stems, or leaves of cassava plants and cause various diseases.
- Some insects affect the plant directly (locusts, beetles and ants); others affect the plant indirectly by the transfer of virus (aphids).
- Rats, goats and wild pigs are probably the most troublesome; they feed on the roots, especially in areas adjacent to forests
Cassava is harvested by hand by raising the lower part of the stem and pulling the roots out of the ground, then removing them from the base of the plant. The upper parts of the stems with the leaves are plucked off before harvest. Cassava is propagated by cutting the stem into sections of approximately 15 cm, these being planted prior to the wet season
Fresh cassava can be preserved like potato, using thiabendazole or bleach as a fungicide, then wrapping in plastic, coating in wax or freezing.