Manihot esculenta Crantz

A large glabrous woody herb or subshrub up to 5 m. tall, rarely a tree 7–8 m. tall.. Root tubers up to 50 cm. long, very farinaceous.. Bark smooth, often reddish.. Young shoots glaucous greenish grey.. Leaves deeply palmatipartite, with 3–5(–7) lobes, rarely simple, shallowly cordate, sometimes slightly peltate, membranous-chartaceous, the lobes oblanceolate, occasionally lanceolate or obovate, 6–14(–17) cm. long, 1–6 cm. wide, acute, gradually acuminate, ± attenuate towards the base, entire, with up to 18 pairs of lateral nerves, midrib scarcely prominent above or beneath, dark green above, glaucous beneath; petiole (0–)5–13(–17) cm. long.. Stipules triangular-lanceolate, 5 mm. long, setaceous-acuminate, ± entire, readily deciduous.. Inflorescence paniculate, 8–11 cm. long; bracts resembling the stipules.. Male flowers: pedicels patent-decurved, 5 mm. long, slender; calyx cylindric-conic in bud, campanulate, the lobes imbricate, triangular, 6 mm. long, 4 mm. wide at the base, subacute, glabrous without, sparingly pubescent within towards the apex, greenish, tinged orange and crimson and sometimes veined with purple, the tube 6 mm. long; long filaments 7 mm. long, short filaments 2.5 mm. long, slender, glabrous, white, anthers 1.5 mm. long, with a tuft of hairs at the apex, pale yellow; disc 10-lobed, concave at the centre, the lobes acute.. Female flowers: pedicels somewhat decurved, 7 mm. long, extending to 2.5 cm. in fruit and thickening to 3 mm.; sepals imbricate, triangular-ovate, 1 cm. long, 5 mm. wide, subacute, glabrous without, pubescent within near the margin; disc shallowly 5-lobed; ovary 2 mm. long, 2 mm. diameter, 6-winged or-angled, pink; styles botryoidal, 2 mm. long.. Fruit ellipsoid-subglobose, 1.5–1.7 cm. long, 1.5 cm. wide, rugulose, 6-winged, the wings undulate-subcrenate, endocarp woody.. Seeds ellipsoid, subpentagonal in section, 1.1 cm. long, 5.5 mm. wide, 3.5 mm. deep, pale grey, sometimes mottled, somewhat shiny, with a caruncle 3 mm. wide.. Fig. 68.

A tropical plant. Plants grow from sea level up to about 1650 m. In Fiji they grow to 900 m. They can grow in poor soil. They can survive drought. It is native to tropical America. It grows between 25°N and 25°S. It needs a rainfall above 750 mm. It suits hardiness zones 10-12. In Yunnan.

Widely cultivated in the tropics for the tuberous roots that provide a starchy substance. "The edible, tuberous root is an extremely important carbohydrate source throughout the tropics; however, it is low in protein and is therefore inferior to yams or taro. The tuber is poisonous when raw, containing prussic (hydrocyanic) acid which is highly water-soluble and the bitter glycoside phaseolutin. These 2 chemicals are freed by an enzyme which is denatured after boiling or roasting, rendering the tuber safe to eat. Other methods of preparation include grinding into meal, pressing to extract the bitter juice, and finally cooking and drying to produce an edible flour. The starch can also be extracted and eaten as tapioca, used as arrowroot or fermented for alcohol. Sweet cultivars have also been selected, with low amounts of the bitter chemicals in the cortex of the tuber. The young leaves may be eaten boiled. The species is easily propagated by cuttings or seed." (Du Puy & Telford 1993: 268).

Cassava is planted from sections of the stalk. Sections about 15-20 cm long of the more mature woody stem are cut and stuck into the ground. They can be completely buried or put at almost any angle and it affects the growth little. Soon roots form and leaves start to sprout from the stalk. Cassava seeds need a soil temperature of 30°C for their germination. Flower and fruit production is more common under lower temperatures such as in highland or less equatorial conditions. It is not necessary to dig a hole to plant cassava and on many soils where the soil is loose it can be planted without digging the soil first. Cassava does not suit waterlogged soils and preferably they should not be too shallow or stony. Cassava can be planted at any time of the year but to get started it needs moisture so is often planted near the beginning of the wet season. The crop once established can survive for several months without rain. The ability to tolerate drought varies significantly with cultivar. During drought less and smaller leaves are produced and leaves die off more quickly but storage roots can be increased in the short term. Because cassava can still grow satisfactorily in poorer soils it is often put last in a rotation after others crops have already been grown on the piece of land. Cassava is more responsive to nitrogen and potassium than phosphorus under many field situations. Nitrogen can increase cyanide levels. Under very acid conditions with high soluble aluminium levels, cassava has been able to achieve and maintain top growth but with significantly reduce root yields. When drainage is good and soil moisture is adequate, cassava stalks can be planted at any orientation from horizontal to vertical, but in very sandy soils horizontal planting is best and and in heavy clay soils vertical planting is best. Because of the slow growth in early establishment stages, soil loss from erosion with heavy rains can be significant. To avoid this planting should be timed so that the maximum vegetative growth is occurring during the heaviest rains. A leaf area index between 2.5-3.5 is optimal for cassava yield. The critical period for weed control is the time from 2-8 weeks after planting. Cassava tuber bulking is delayed under shaded conditions. Yields are also reduced. In mixed cropping situations using crops which mature early, allowing the cassava time to recover, is one possible strategy. For optimum production shading should be avoided. Cassava takes about 10 to 12 months to produce mature tubers in the lowlands tropics although some varieties produce a smaller yield earlier. Yields in the range of 20-45 t/ha have been recorded for 12-14 month crops. The plants can be left growing and the tubers stored in the soil for considerable time. Crops of 24 months duration occur. Once the tubers have been dug they do not keep for more than a few days. Pre-harvest pruning of plants increases the storage time of tubers after harvest. Spacing and plant density varies with soil climatic conditions and variety. Plant densities from 10,000 to 30,000 plants per hectare are used. Plants from the higher density crops have been shown to have quick post harvest deterioration. Mulching has given significant yield increases in some conditions. It also reduces the incidence and damage of some root boring insects.